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Hindawi Publishing CorporationJournal of NanoparticlesVolume 2013 Article ID 737831 11 pageshttpdxdoiorg1011552013737831

Research ArticleMicrowave-Assisted Synthesis of MixedMetal-Oxide Nanoparticles

Akrati Verma1 Reena Dwivedi1 R Prasad1 and K S Bartwal2

1 School of Chemical Sciences Devi Ahilya University Indore 452001 India2 Laser Materials Development amp Devices Division RRCAT Indore 452013 India

Correspondence should be addressed to K S Bartwal bartwalksyahoocoin

Received 21 January 2013 Accepted 9 February 2013

Academic Editor Amir Kajbafvala

Copyright copy 2013 Akrati Verma et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Nanoparticles of mixed metal oxides ZrO2 ZrTiO

4 and ZrV

2O7were prepared by microwave-assisted citrate sol-gel and solution

combustion method The prepared nanoparticles were characterized for their structural details using XRD and TEM techniquesThe broadening of Raman bands is ascribed to local compositional fluctuations or local positional disordering produced due torandom distribution of Zr4+ and Ti4+between equivalent sites The XPS spectra confirm the incorporation of Ti in ZrO

2and

suggest Zr as well as Ti in +4 oxidation state Gelation and fast combustion seem to be the reason for smaller particle sizesZrV2O7nanocrystalline material was synthesized by microwave- assisted solution combustion method Low angle powder XRD

measurements confirm the mesoporous nature of the prepared material The effect of calcination temperature on the phase trans-formation of the materials has been investigated Among tetragonal monoclinic and cubic phases the monoclinic phase is pre-dominant at higher calcinations temperature The XPS confirms the incorporation of V

2O5in ZrO

2and suggests that Zr and V

are in the same oxidation state (+4) The average particle sizes for ZrO2 ZrTiO

4 and ZrV

2O7were found to be in the ranges of

5ndash10 nm 2ndash5 nm and 10ndash50 nm respectively

1 Introduction

Combination of two metal oxides M1O and M

2O can be

either a simple mechanical mixing involving weak van derWaals forces or a chemical possessing chemical linkages of thetype M

1-O-M

2 The physicochemical properties of the latter

combination will be entirely different from the simple combi-nation of individual oxides (mechanical mixture)The degreeof dispersion in the chemical rout depends on preparationmethod and synthetic conditions Because of this many dif-ferent synthetic routes for mixed metal oxides have beendeveloped Some of the popular routes for preparation ofmixed oxides are coprecipitation sol-gel method condensedphase combustion andmicrowave-assisted solution combus-tion method

Coprecipitation (wet precipitation) is the most widelyused method for oxide synthesis In this method hydroxideof the metals is precipitated from an aqueous solution of themetal salt by titrating it with ammonia solution The hydrox-ide is washed dried and calcined to get the metal oxide Sol-gel method is used to prepare metal oxides by hydrolysis andcondensation of metal alkoxides M(OR)

119911

M(OR)119911+ 119909HOH 997888rarr M(OR)

119911minus119909(OH)119909+ 119909ROH (1)

The reaction follows an SN2 mechanism in which the nucle-ophile OHminusadds to the M+ and increases its coordinationnumber in the transition state

H

HO120575minus+ +M120575+ O120575minus R

H120575+ H120575+

OH OHR

M M ROHH

O120575minus+ M O O120575minus R (2)

2 Journal of Nanoparticles

The H+ changes its position to alkoxy group producing aprotonated ROH species which is subsequently eliminatedand metal hydroxide is produced Production of MgO isa typical example The rate of hydrolysis and condensationdepends on (1) electronegativity of the metals atom (2)ability of the metal atom to increase its coordination number(3) steric hindrance of the alkoxy group (4) solvents (5)molecular structure of themetal alkoxide (6) hydrolysis ratioℎ = H

2OMetal and (7) catalyst The rate of hydrolysis of

Ti(OEt)4is 107 times faster than that of Si(OEt)

4 This can be

attributed to the ability of Ti to expand its coordination num-ber from4 to 6 For the same reason the hydrolysis of Sn(OR)

4

is much faster compared to Si(OR)4

Most advanced ceramics are multicomponent systemshaving two or more types of cations in the lattice It is there-fore necessary to prepare gels of high homogeneity in whichcations of various kinds are distributed uniformly at anatomic scale through M-O-M bridges A major problem informing homogeneous multicomponent gel is the unequalhydrolysis and condensation rates of themetal alkoxidesThismay result in chemical inhomogeneities leading to highercrystallization temperatures or even undesired crystallinephases Several approaches have been attempted to overcomethis problem including partial prehydrolysis of less reactiveprecursors matching of hydrolysis rates by chemical modifi-cation with chelating ligands and synthesis of heterometallicalkoxides Conventional self-propagating high temperaturesynthesis (SHS) or condensed phase combustion is associatedwith difficulties like large particle size of nanomaterials andhigh reaction temperature of about 2000∘C Combustion ofmetal oxides by Mg in the presence of NaCl produces smallparticles of metals coated with NaCl Subsequent treatmentof the powder with dilute acid removes MgO impurity Metalcan be recovered by washing the sample with water

Microwave-assisted method of oxide synthesis is gainingpopularity because of its high rate of reaction efficient heattransfer and environmental friendly nature In this processmaterial is directly heated by radiation instead of indirectheating by thermal sources leading to higher temperaturehomogeneity in the reaction mixture In this process of heat-ing microwave radiation interacts with the polar moleculespossessing dipole moment and makes them reorient throughrotation A large number of molecules try to orient togetherresulting in collision and production of heatThusmicrowaveheating is energy conversion method in which electro-magnetic radiation is converted into heat energy ratherthan heat transfer by convection in conventional heat-ing In microwave-assisted solution combustion synthesis(MWSCS) an aqueous solution of metal nitrate (oxidant) andfuel (urea citric acid) is subjected to a microwave heatingfor few minutes to obtain a viscous gel which on drying andcalcination produces the metal oxidemixedmetal oxideThesolution combustion method seems to be modification ofthe conventional oxalate method which is used for preparingmetal oxides and supported metal oxides The citrate gel de-composition process is better known as a thermally inducedanionic oxidation-reduction reaction In the process chelatesare formed between metal ions facilitating atomic scale dis-tribution of ions in a polymer network Heating of this resin

causes the breakdown of the polymer and a solid amorphousprecursor material is finally obtained On subsequent heatingbetween 500 and 900∘C the cations are oxidized to form therespective metal oxides Microwave-assisted MVSCS tech-nique can be used for preparingmaterials or catalysts catalystsupport fuel cells capacitors Li-ion rechargeable batteriesdye-sensitized solar cells solid oxide fuel cells (SOFC) anddirect methanol fuel cells (DMFCs)

The development of zirconia (ZrO2) nanoparticles has

attracted much attention due to their multifunctional char-acteristics Nanoparticles have been recognized to havepotential in the area of photonic applications It has severalapplications such as solid oxide fuel cell biosensors H

2gas

storagematerial oxygen sensor catalyst and catalyst support[2ndash5] In addition zirconia is used as piezoelectric materialelectrooptic material and dielectric material [6ndash8] It is alsoused as support to disperse various noble and transition met-als for distinct catalytic applications Zirconia is a well-knownsolid acid catalyst and an n-type semiconductor materialZrO2is also used as toughening ceramics in thighbone and

oral planting [9] The existence of metastable tetragonal (t-ZrO2) at low temperature has been synthesized by several

methods Some of the methodologies such as oxidation ofZrCl2by molecular oxygen [10] molten hydroxides method

[11] nonhydrolytic sol-gel reaction between isopropoxideand ZrCl

4[12] and sol-gel template technique [13 14] are

developed to prepare nanocrystalline ZrO2

The traditional preparation of zirconium titanate (ZrTiO4)

ceramic is based on solid-state reaction between the TiO2

and ZrO2powders at high temperatures (above 1400∘C)

[15] In order to improve the functional properties of theceramic material heat treatments are generally necessarywhich consume high amount of energy Chemical methodbased on Coprecipitation of the reactive precursors wasdeveloped to prepare powders with a high purity and lowtreatment cost after reaction [16] Low temperature synthesisof zirconium titanate has been reported by Karakchiev et al[1] and Dos Santos et al [17] Zirconium titanate possessinga layered wolframite-type structure (ABO

4) with space group

P2a finds applications asmicrowave components As catalystand catalyst supports ZrTiO

4is employed for a wide variety

of catalytic applications both in liquid and gaseous phases [1819] Recently it has been reported that the oxide nanoparticlesare promising for photonics and their monodispersion andappropriate contact with the surrounding medium are verycrucial parameters [20 21]

Vanadium incorporated zirconia (V2O5-ZrO2) is ameso-

porous material and is very useful catalyst Nanoporousmaterials consist of a regular organic or inorganic frameworksupporting a regular porous structure A mesoporous mate-rial is a material containing pores with diameters between2 and 50 nm The 120572-phase (cubic) of ZrV

2O7is the stable

structure at ambient conditions It consists of ZrO6octahedra

whose corners share their oxygen atomswithVO4tetrahedra

Vanadiumoxide catalysts supported on differentmetal oxidesare widely used inmany industrial reactions such as selectivecatalytic reduction of NO with NH

3 ammoxidation of alkyl

aromatics and the selective oxidation of hydrocarbons Prop-erties of supported vanadium catalysts depend on a variety

Journal of Nanoparticles 3

of factors such as percentage of vanadium loading methodof preparation interaction and nature of the support [22]Various supporting oxides used for vanadium loading includeAl2O3 TiO2 SiO2 ZrO

2 MgO and HfO

2[23 24] Among

all these oxides ZrO2is a better choice as it interacts with

vanadium relatively strongly preventing its sintering andhelps in producing highly dispersed vanadium on ZrO

2

Besides ZrO2is thermally and chemically stable at the dif-

ferent reaction conditions Solution combustion synthesis isa versatile low-cost simple and rapid process which allowseffective synthesis of a variety of nanosize materials Thisprocess involves a self-sustained reaction in homogeneoussolution of different oxidizers (eg metal nitrates) and fuels(eg urea glycine and hydrazides) [25 26]

The objective of the present work is to synthesize zir-conium oxide zirconium titanate and zirconium vanadatenanocrystalline powder by microwave-assisted method Thecombustion synthesis for preparing ZrO

2has been per-

formed under microwave using citric acid as fuel and zir-conium oxychloride as oxidizer The ZrTiO

4particles were

prepared using titanyl nitride and zirconium oxychloride asprecursors The ZrV

2O7nanoparticles were synthesized by

microwave-assisted solution combustion method The pre-pared nanoparticles were characterized for their structure-property relationship The particle size and crystalline phaseof the catalysts were determined by powder X-ray diffraction(XRD) The TEM technique was used to confirm the forma-tion of single phase material with nanocrystalline particlesRaman and XPS spectroscopy techniques were used to char-acterize the structure and electronic properties The presentproblem was undertaken with an aim (1) to develop a versa-tile effective low-cost simple and fast solution combustionassisted method for synthesis of these zirconia-based oxidenanoparticles and (2) to characterize the prepared nanopar-ticles by employing various physicochemical methods

2 Experimental Details

Zirconia (ZrO2) nanoparticles were prepared by citrate sol-

gel method High purity chemicals zirconium oxychlo-ride (SD Fine Chemicals) and anhydrous citric acid(LOBA Chemie Pvt Ltd) were used as precursors In thepresent set of experiments 978 g of zirconium oxychloride(ZrOCl

2sdot8H2O)wasmixedwith 768 g of citric acid (C

2O4H2)

in a 250 mL corning glass beaker Demineralized water wasadded to have homogeneous slurry of pH 2The solution wasevaporated to dryness by exposing it to microwave for 2minThe material swells into a white colored gel The productobtained was ground and kept for calcination in a tubularfurnace at a temperature of 450∘C for 4 h On calcinationsa black colored residue was obtained which was ground ina motor pastel to make a fine powder Similarly zirconiumtitanate (ZrTiO

4) nanoparticles were prepared by citrate sol-

gel method Zirconium oxychloride anhydrous citric acidand titanyl nitrate were used as starting materials The titanylnitrate was prepared by reacting tetrabutyl orthotitanate withnitric acid and evaporating the resulting mixture to drynessThe replacement of Zr by Ti was optimized and two sets of

compositions in Zr Ti ratio 1 01 and 1 1 were prepared Ina typical preparation 32 g of ZrOCl

2sdot8H2O 029 g of titanyl

nitrate and 35 g of citric acid were used for 1 01 ratio ofZr Ti (named ZT1) and 32 g of ZrOCl

2sdot8H2O 295 g of

titanyl nitrate and 615 g of citric acid were used for the 1 1ratio of Zr Ti (named ZT2) These precursors were mixedin a 250mL corning glass beaker and enough demineralizedwater was added to have homogeneous slurry of 2 pH Thewell-mixed solution was evaporated to dryness by exposingit to microwave for 2min This step of drying in microwaveoven was optimized and the time of 2min was found suitablefor this compositionThe driedmaterial was ground and keptfor calcination in a resistive heating tubular furnace at a tem-perature of 400∘C for 4 h A grayish colored residue wasobtained on calcination which was again ground in a motorpastel to make a fine powder Both compositions of ZrTiO

4

with Zr Ti ratio 1 01 and Zr-Ti ratio 1 1 were preparedwith the same procedure in similar conditionsThese sampleswere named as ZT1 and ZT2 respectively and were used forvarious physicochemical studies

Mesostructured vanadiumoxide supported on zirconiumoxide was synthesized by microwave-assisted solution com-bustion method [25 27] Zirconium oxychloride (SD FineChemicals) and ammonium metavanadate and urea (LOBAChemie Pvt Ltd) were used as starting materials In atypical preparation of 10 vanadium doped zirconia (ZV10)a solution of zirconium nitrate (prepared by mixing 58 g ofzirconium oxychloride with 12mL of 1 2 HNO

3) is mixed

with another solution prepared by mixing 023 g of NH4VO4

in 50mL of water The final solution was mixed with 12 gof urea and fired in a muffle furnace at 200∘C for 15minThe material swells into a yellow colored gel The productobtainedwas ground and kept for calcination in a tubular fur-nace at a temperature of 400∘C for 4 h On calcination a greencolored residue was obtained The prepared powder wasground several times before putting it in specimen holder tominimize the possible preferred orientation effects For thepreparation of all the ZV

119909materials 1 1 molar ratio of urea to

metal oxide (Zr +V)119909was taken Four different samples with

varying V2O7concentrations were prepared The samples

were named according to V2O7concentrations of 2 5 8 and

10mol and named as ZV2 ZV5 ZV8 and ZV10 respec-tively

The crystallite sizes and structural morphology wereinvestigated by transmission electron microscopy (TEM) inhigh-resolution mode Philips make Tecnai G2-20 (FEI)electron microscope operating at 200 kV was used for TEMexperiments Sample for TEM observation was prepared bysuspending the particles in ethanol by ultrasonification anddrying a drop of the suspension on a carbon coated coppergrid Raman spectrum in the range 50ndash4000 cmminus1 was re-corded using Labram HR 800 micro-Raman spectrometerwith 488 nm wavelength Ar+ laser source at the energy of253 eV with recording time of 10 sec The core level X-rayphotoelectron spectroscopy (XPS) spectra of ZrTiO

4and

ZrV2O7were measured using Omicron Nanotechnology

(EA1-25) photoelectron spectrometer with Al K120572radiation

(119864 = 14866 eV) as excitation sourceThe base pressure of theanalysis chamber of the system was less than 5 times 10minus10mbar


20 40 60 80

220

101

110 21

1

112

Inte

nsity

(au

)ZrO2

2120579

(a)

20 30 40 50 60 70

ZT1202

22202

2

200

311

220

130

002

111

110

Inte

nsity

(au

)

ZT2

2120579

(b)

20 30 40 50 60 70

311220

00211

1

2120579

ZrO2

400 ∘C

600 ∘C

800 ∘C

Inte

nsity

(au

)

(c)

Figure 1 Representative powder XRD pattern for (a) ZrO2 (b) ZrTiO

4(ZT1 and ZT2) nanoparticles calcined at 400∘C and (c) ZrV

2O7

(ZV10) nanoparticles calcined at different temperatures

during the experiments Energy scale of the spectrometer wascalibrated by setting the measured Au 4f

72and Cu 2p

32

binding energies to 8400 plusmn 005 and 93266 plusmn 005 eVrespectively with regard to 119864

119865 The energy drift due to

charging effects was calibrated taking the XPS C 1s (2850 eV)core-level spectrum of hydrocarbons

3 Results and Discussion

It is known that the main crystal phases of ZrO2are cubic

(c) tetragonal (t) and monoclinic (m) The IR frequenciesfor cubic tetragonal and monoclinic phases are 480 435and 270 cmminus1 respectivelyThis indicates that phonon energyof the ZrO2 host varies in the crystal phases The mono-clinic phase is thermodynamically stable up to 1100∘C thetetragonal phase exists in the temperature range 1100ndash2370∘Cand the cubic phase is found above 2370∘C The nanoparti-cles of tetragonal zirconium oxide (t-ZrO

2) were prepared

by microwave-assisted citrate sol-gel technique Zirconiumtitanate ZrTiO

4 with two different Zr Ti ratioswas prepared

to understand the complete replacement of Zr ion by Ti TheZr Ti ratios taken were 1 01 (ZT1) and 1 1 (ZT2) Thesesamples were prepared by microwave-assisted citrate sol-gelmethod The microwave was used during the sol-gel dryingprocess to make the particles more homogeneous in ZrTiionic ratio The prepared samples were subjected to variouscharacterization studies to understand dispersion of Ti ionsand the role of microwave in preparation Zirconia supportedvanadate (ZrV

2O7) was synthesized by microwave-assisted

solution combustion method The two-dimensional vanadiaspecies with tetrahedral coordination appear on the surfaceof the ZrO

2and expand in size with increasing V

2O5con-

centration ZrV2O7is formed as a consequence of zirconia

migration into theV2O5crystallitesThe prepared nanoparti-

cles were found having mesoporous structureThe structuresof the zirconia support and of the dispersed vanadia werecharacterized The prepared nanoparticles were investigatedfor their phase and structure by powder XRD using Cu K

120572

radiation (120582 = 15406 A Rigaku Geiger Flex X-ray diffracto-meter) The powder XRD data were collected in the 2120579 rangefrom 20 to 80 degrees with the scan rate of 2∘ per minute


0 05 1 15 2 25 3

(B)

(D) (C)

(A)

Inte

nsity

(au

)

(A) ZV2 (B) ZV5

(C) ZV8 (D) ZV10

2120579

Figure 2 Low angle XRD pattern of ZV2 ZV5 ZV8 and ZV10calcined at 400∘C

Theprepared powderwas ground several times before puttingit in specimen holder to minimize the possible preferredorientation effects Powder XRD patterns of the preparedZrV2O7nanoparticles calcined at different temperatureswere

recorded The representative powder XRD for all the threesamples is shown in Figures 1(a) 1(b) and 1(c) XRD patternshown in Figure 1(a) reveals the fact that the single tetragonalphase of ZrO

2is crystallizedThe calcination temperature has

important role to play in formation of crystalline phase andthe particle size The calcination temperature was optimizedand 450∘C was found to be effective to crystallize the desiredtetragonal phase It was observed that the full width at halfmaximum of the reflection peaks decreases and also becomessharp as the calcining temperature increases This suggeststhat the crystallinity of prepared zirconia nanoparticles isincreasing at higher temperatures The XRD patterns havebeen indexed and found matching with the t-ZrO

2(JCPDF

card file no 79-1771) The lattice parameters were calculatedfor t-ZrO

2from the XRD data The parameters were 119886 =

5083 A 119888 = 5185 A and the tetragonality 119888119886 = 10201 Thediffraction characteristic peaks were obtained with the (h k l)values of (101) (110) (112) (211) and (220) The particle sizeswere calculated from FWHM (full width half maximum) ofreflections of t-ZrO

2structured zirconia nanoparticles using

Debye-Scherer formula [28]

119863 =09120582

(120573 cos 120579) (3)

where 119863 is the average crystallite size in nm 120582 is the wave-length of source X-ray (0154 nm) and 120573 (in radian) is the fullpeak width at half maximum The particle sizes were foundvarying sim5ndash10 nm range

It is known that the zirconium titanate solid solution withZr Ti molar ratio ranging from 1 1 to 1 2 is the onlystable binary compound in the ZrndashTindashO system Two

structural modifications known for this system are high-temperature disordered Zr

1minus119909Ti119909O4(Ti-excess) and low-

temperature ordered ZrTiO4 The XRDs for the samples

ZT1 and ZT2 are reproduced in Figure 1(b) which indicatethe formation of ZrTiO

4orthorhombic phase which is

closely matching with JCPDS file no 34-415 To a firstapproximation this major phase has orthorhombic structureof 120572-PbO

2with space group Pbcn with the cell parameters

119886 = 480 A 119887 = 549 A and 119888 = 503 A Most of thepeaks for the samples ZT1 and ZT2 are matching the onlydifference being the intensity of the peaks which is differentfor Zr-rich composition (ZT1) The diffraction characteristicpeaks for this phase were obtained with the (h k l) valuesof (011) (111) (200) (220) (022) and (311) The doubletsobserved in the XRD pattern for ZrTiO

4at 2120579 values 35 37

and 54 are due to the presence of small amount of secondaryphase (Zr

5Ti7O24) of Ti-rich phase in Zr-Ti system It has

been known that some small amounts equation of ZrO2and

TiO2are also expected to be formed during the process The

average particle sizewas calculated from (111) diffraction peakusing Scherrerrsquos and the average particle size was calculatedto be sim48 nm ZT1 and sim614 nm for ZT2

XRD pattern for pure ZrO2material calcined at 400∘C

and 10wt V2O5supported on ZrO

2calcined at different

temperatures in the range of 20∘ndash70∘ is shown in Figure 1(c)The pattern has been indexed with the tetragonal ZrO

2

(JCPDS card file no 81-1551) and cubic ZrV2O7(JCPDS card

file no 16-0422) The absence of vanadia or vanadate peaks(2120579 = 203∘ and 262∘) in the sample calcined at 400∘C and600∘C can be noticed The appearance of the vanadia peaksin the samples calcined at 800∘C is clearly seen The presenceof these peaks with lower intensity in the sample calcined at800∘Cconfirms that the vanadium ions have occupied the zir-conium ions at their lattice positions and high dispersion ofvanadia ions on zirconium oxide surface [29] On calcinationat higher temperatures the full width at half maximum of thediffraction peaks decreasesThis decrease in FWHMsuggeststhat the sizes of prepared zirconium vanadate nanoparticlesare increasing at higher temperaturesWhen zirconiumvana-date sample was calcined at 400∘C and 600∘C a very sharppeak appeared at 3034∘ which can be ascribed to tetragonalphase On calcination at 800∘C two sharp peaks appeared at282∘ and 31∘ which is ascribed to the monoclinic phase ofZrO2[30] The average particle size was calculated from (111)

diffraction peak using Schererrsquos equation and the averageparticle size was calculated to be 16 nm 27 nm and 4963 nmrespectively for 10 wt zirconium vanadate samples calcinedat 400∘C 600∘C and 800∘C Low angle powder XRD patternof the prepared nanoparticles calcined at 400∘C for 4 h wasrecorded in order to explore structural feature of zirconiumsupported mesoporous vanadium materials Figure 2 showsthe low angle powder XRD pattern The appearance of peakin low angle region at 03∘ confirms themesoporous nature Ithas been known that the presence of sharp peak in low angleregion confirms the disordered wormhole type mesoporosityin ZrV

2O7[31] The increase in the intensity of the peak

present at 03∘ with increasing V concentration suggests theenhancement in mesoporosity in the material


(a) (b)

Figure 3 (a) RepresentativeTEMmicrograph for ZrO2sample annealed at 450∘C (b)High-resolutionTEMmicrograph for samples annealed

at 450∘CThe corresponding SAED patterns are inserted into micrographs

(a) (b)

Figure 4 (a) Representative TEM micrograph for ZrTiO4sample (b) High-resolution TEM micrograph for the same sample The

corresponding SAED patterns are inserted into micrographs

Transmission electronic microscopy (TEM) in high-re-solutionmode is the best tool to analyze the morphology andthe sizes of the prepared nanoparticles [32ndash34] Figures 3(a)and 3(b) show the representative TEM micrographs takenfor the ZrO

2samples calcined at 450∘C The corresponding

selected area electron diffraction (SAED) patterns areinserted into the micrographs Figure 3(a) shows a typicalTEM image for the dried powders The powders are very fineand agglomerated Electron diffraction analysis reveals thatthey have amorphous characteristics due to small particlesizes The micrograph shown in Figure 3(a) indicates theformation of nanoparticles with sizes ranging from few nano-meters to few tens of nanometersThe corresponding diffrac-tion pattern shows few clear spots along with connecting dif-fraction rings The presence of spots along with the streaksshows the presence of crystallite of reasonably sufficient sizesto diffract The connecting streaks indicate the short-rangeorder due to presence of some smaller size particles as wellThe high-resolution electron micrograph for the samplesannealed at 450∘C is shown in Figure 3(b) The clarity in thefringe patterns inside the crystallite indicates the formation of

single phase ZrO2with the long-range order in the structure

The corresponding SAED pattern is inserted into the micro-graph The clear spots in SAED pattern suggest that thecrystallites are of sufficiently large size The absence of ringsin the SAED pattern is indicative of the crystalline orderlarger particle size and long-range order in the crystallitesThe TEM results also suggest the successful preparation oftetragonal phase of ZrO

2nanocrystals with the crystallite

sizes ranging sim5ndash10 nmThe samples of ZrTiO

4(ZT2) with the Zr Ti ratio of 1 1

calcined at 400∘C were also analysed using TEM and themicrographs taken are shown in Figures 4(a) and 4(b) Corre-sponding selected area electron diffraction (SAED) patternsare inserted into the micrographs The micrograph shown inFigure 4(a) shows the formation of nanoparticles The SAEDpattern inserted into the micrograph shows the few sharpspots along with connecting diffuse rings The smaller sizeparticles are responsible for the connecting rings whichsuggests the short-range order The high-resolution electronmicrograph (HRTEM) for the sample ZrTiO

4(ZT2) is shown

in Figure 4(b) The fringe patterns indicate the formation


(a) (b)

Figure 5 Representative HRTEM images of (a) ZV8 and (b) ZV10 compositions The corresponding SAED patterns are inserted into themicrograph

of single phase ZrTiO4with the long-range ordering in the

structure The corresponding SAED pattern is inserted intothe micrograph Spots along with rings in the SAED patternsuggest the larger particle size and short-range order in thecrystallites These results on TEM suggest the preparation ofthe desired phase of ZrTiO


sizes ranging sim2ndash5 nmThe high-resolution TEM images and corresponding

selected area electron diffraction (SAED) patterns forZrV2O7samples (ZV8 and ZV10) calcined at 400∘C are

shown in Figures 5(a) and 5(b) HRTEM micrograph shownin Figure 5(a) confirms the formation of nanoparticles withvarying sizes The particle sizes are in sim20ndash30 nm range andsufficient to diffract and produce SAED pattern The SAEDdiffraction pattern inserted into themicrograph (Figure 5(a))shows the presence of few sharp spots alongwith diffuse spotsand connecting ring The position of the reflections (shownby arrow) in the electron diffraction pattern and broadeningof the rings indicate the presence of small randomly orientedV-Zr mixed oxide particles The HRTEM for ZV10 shown inFigure 5(b) shows that the particle sizes increase with increas-ingV concentration Sharp and clear spots along the SADpat-tern in Figure 5(b) suggest the long-range order between thecrystallitesTheparticle sizes are insim20ndash50 nm range and suf-ficient to diffract and produce sharp and clear SAED patterncompared to ZV8 The previous TEM results of diffractionand high-resolution mode suggest the successful preparationof the cubic ZrV

2O7nanoparticles with the particle sizes

ranging sim20ndash50 nm The TEM results show that there is nosecondary phase formation due to vanadia separation Theformation of well-crystallized ZV nanoparticles is clearlyseen in the micrographs The particle size of the as-preparedmaterials was found to increase with the increase in the Vconcentration

It has been known that the Raman spectroscopy can beused to determine the symmetry of a crystal system for oxidematerials as it is very sensitive to the polarizability of theoxygen ions In fact Raman spectroscopy is a technique moresensitive to short-range order than X-ray diffraction and itcan show the peaks for anatase or rutile as well as monoclinic

zirconia along with that of tetragonal zirconia Ramanspectroscopy has been performed on all the nanocrystallinesamples of ZrO

2and ZrTiO

4samples The Raman spectra of

ZrO2calcined at the temperatures of 600∘C and 800∘C are

plotted in Figure 6(a) The assignment of the observed bandswas made on the basis of the comparison of the observedspectra with those of reported in the literature [1 35 36]Thevibrational Raman active modes are classified as

Γ = 1198601119892+ 21198611119892+ 3119864119892 (4)

In 1198601119892

mode oxygen atoms move in the 119911-direction onlyThe 119861

1119892modes also involve motion in the 119911-direction how-

ever now both Zr and O atoms participate In 119864119892modes Zr

as well as O atoms move in the 119909-119910 plane In Figure 6(a) theplot (A) represents the Raman spectra for the sample calcinedat 400∘CThe band that appeared at 643 cmminus1 can be assignedto 1198601119892

mode since it involves movement of two oxygenatoms only and is expected to appear at higher wavenumberThe next two bands that appeared at 470 and 382 cmminus1 areassigned to doubly degenerate 119864

119892modes on the simple rea-

soning that these two modes also do not involve movementof Zr atoms The remaining three modes namely two 119861

1119892

modes and one 119864119892modes are assigned to the remaining three

bands appeared at 259 146 and 123 cmminus1 respectively Thespectrumof sample calcined at 600∘C is shown as curve (B) inFigure 6(a) The previous bands that appeared in the Ramanspectra for both samples are assigned to t-ZrO

2 In addition

few faint bands at 563 536 381 293 and 176 cmminus1 have ap-peared which are due to the coexistence of small amount ofmonoclinic phase

The Raman spectra of ZrTiO4(ZT1 and ZT2) are shown

in Figures 6(b) and 6(c) The location of band positions isshown in Table 1The band positions recorded by Karakchievet al [1] for ZrO

2are shown in Table 1 for comparison

ZrTiO4with orthorhombic symmetry (space group Pbcn

point group mmm) and two formula units in a unit cellhave 33 optically active modes of vibration 18 of whichare Raman active and 15 are infrared active phonon modesTheir distributions are as follows Raman 4119860

119892 51198611119892 41198612119892


0 1000 2000

Inte

nsity

(au

)

146

470259

123

382

(B)

(A)643

(A) ZrO2 600 ∘C

(B) ZrO2 800 ∘C

Wavenumber (cmminus1)

(a)

200 400 600 800 1000 1200

Inte

nsity

(au

)

ZT1


(b)

200 400 600 800 1000 1200

Inte

nsity

(au

)

ZT2


(c)

200 400 600 800 1000 1200

(C)(B)

(A)


(A) ZV10 400∘C

(B) ZV10 600∘C

(C) ZV10 800∘C

Inte

nsity

(au

)

(d)

Figure 6 Raman spectra of (a) ZrO2precipitated at pH 2 and calcined at different temperatures (b) ZT1 and (c) ZT2 calcined at 400∘C and

(d) ZV10 calcined at (A) 400∘C (B) 600∘C and (C) 800∘C

51198613119892

and Infrared 4119860119906 41198611119906 31198612119906 41198613119906 Raman line shape

analysis has also been studied by Kim et al [37 38] andKrebs and Condrate [39] The number of observed bandsin the present recording is much less as compared to thoseobtained for the samples prepared by ceramics due to thefact that (a) band positions are at lower wavenumbers (b)bands are too weak to be observed (c) bands are hidden dueto overlap by other bands and (d) lower degree of orderingin nanocrystalline ZrTiO

4 The bands due to that appeared

in nanocrystalline ZrTiO4samples are broader compared to

those in ZrO2and can be attributed to local compositional

fluctuations or local positional disordering produced due to

random distribution of Zr4+ and Ti4+ between equivalentsites in the crystal lattice

In the similar experimental setup the representativeRaman spectra for ZrV

2O7(ZV10) samples calcined at 400∘C

600∘C and 800∘C are plotted in Figure 6(d) and the assign-ments of bands aremade on the basis of reported assignments[1 35ndash39] and are given in Table 2 14 Raman-active modescentred at 144 176 187 269 282 384 406 474 654 705 773889 996 and 1044 cmminus1 were detected The ZrV

2O7crystals

contain the VO4tetrahedra and ZrO

6octahedra in the struc-

ture The modes centred at 889 996 and 1044 cmminus1 areassigned to symmetric stretching of the VO

4tetrahedra


0 200 400 600 800 1000 1200

Zr 3p

Inte

nsity

(au

)

BE (eV)

ZrTiO4

Ti 2pTi 2s

O KLLO 1s

Zr 3p

C 1S

Zr 3d

Zr 4p

(a)

Inte

nsity

(au

)

0 200 400 600 800 1000 1200BE (eV)

ZrV2O7

O KLL

O 1s

Zr 3pC 1SZr 3d

Zr 4p

(b)

Figure 7 Representative survey XPS spectra of (a) ZrTiO4and (b) ZrV

2O7nanoparticles calcined at 400∘C

Table 1 Observed bands (cmminus1) and their assignments in ZT1 ZT2and ZrO2

ZT1 ZT2 ZrO2 Reference [1]141 (VS) 141 (VS) 146 (VS) 145 (VS)388 (S) 395 (S) 382 (S) 405 (S)

470 (M)572 (M) 514 (S) 515 (M)652 (M) 642 (S) 643 (M) 635 (S)850 (W) 839 (VVW)986 (W)1085 (W)VS very sharp S sharp M medium W weak VVW very very weak

The modes centred at 705 and 773 cmminus1 are assigned to theasymmetric stretching of theVO

4tetrahedraThemodes cen-

tred at 269 282 and 384 cmminus1 are assigned to the symmetricZrO6octahedral stretching and at 406 cmminus1 to the asymmet-

ric ZrO6octahedral bending The modes centred at 474 and

654 cmminus1 are assigned to ZrO2tetragonal stretchingThe low

frequency bands that appeared at 144 176 and 187 cmminus1 areassigned to lattice vibrations The sharpness in the peaks isobserved with the increase in calcination temperature indi-cating increase in particle size with temperature Theseresults are consistent with previous studies of V

2O5ZrO2

which have also confirmed the formation of ZrV2O7on cal-

cination at high temperatures [40 41]X-ray photoelectron spectroscopy (XPS) method has

been used to study experimentally the valence-band andcore-level spectra as well as the energy distribution of someoccupied valence states of the constituent atoms of ZrTiO

4

XPS valence-band and core-level spectra of ZrTiO4were

measured using the UHV analysis system Al K120572 radiation(119864 = 14866 eV) and hemispherical analyzer operating atconstant pass energy of 40 eV were used as a source of XPSspectra excitationTheXPS survey spectrumof ZrTiO

4(ZT2)

Table 2 Observed Raman bands (cmminus1) and their assignment forZrV2O7 calcined at 800∘C

Observed bands (cmminus1) Assignment144 (s) 176 (w) 187 (w) Lattice889 (s) 993 (s) 1044 (m) VO4 (symmetric)705 (m) 773 (m) VO4 (asymmetric)474 (s) 654 (m) ZrO2 (tetragonal)269 (s) 282 (m) 384 (w) ZrO6 (symmetric)406 (m) ZrO6 (asymmetric)s strong m medium w weak

is shown in Figure 7(a) It has been reported that the X-rayemission of Ti L120572 Zr L120573

215 and O K120572 bands on a common

energy scale indicates that Ti 3d Zr 4d and O 2p statescontribute throughout the valence-band region of ZrTiO

4

[42] The XPS spectra show that the XPS bands for Zr 3d Zr3p and Ti 2p core-level spectra are simple spin doublets withthe XPS Zr 3d

52 Zr 3p

32 and Ti 2p

32core-level binding

energies appearing at 190 342 and 440 eV respectively whichcorrespond to those of titanium and zirconium in the formalvalence state of Zr4+ and Ti4+ [43]The previous results revealthat in ZrTiO

4the binding energy positions of Ti 2p and O

1s core levels match well with the reported values Similarlythe XPS of ZrV

2O7was taken using UHV analysis system

with Al K120572 radiation (119864 = 14866 eV) and hemisphericalanalyzer operating at constant pass energy of 25 eV beingused as a source of XPS spectra excitation Figure 7(b) showsthe XPS survey spectrum of ZrV

2O7 The spectra confirm

the presence of vanadium zirconium carbon and oxygen[42 44]The peak at 517 eV is due to V 2p

32and indicates the

presence of V5+ species The peak that appeared at 5244 eVcan be assigned to V 2p

12 and shift in this peak from 523 eV

to 5244 eV can be ascribed to change in the oxidation statefrom V4+ to V5+ The strong peak that appeared at 5376 eVis assigned to O 1s The peak at 2915 is due to C 1s and


the doublet that appeared at 3401 eV and 3533 eV can beassigned to Zr 3p

32and Zr 3p

12 respectively

The binding

energy positions of the species (V O and Zr) obtained in thepresent investigations match well with the reported values

4 Conclusion

Microwave-assisted method of oxide synthesis is importantdue to its high reaction rate efficient heat transfer and envi-ronmental friendly nature In this process material is directlyheated by radiation leading to higher temperature homo-geneity ZrO

2and ZrTiO

4nanoparticles were synthesized by

microware assisted citrate sol-gel method Nanoparticles ofV2O5supported on ZrO

2were synthesized by microwave-

assisted solution combustion method The formation oftetragonal crystalline phase (t-ZrO

2) was confirmed by pow-

der XRD analysisThe low angle powder XRDmeasurementsconfirm the mesoporous nature of ZrV

2O7and formation

of single phase material up to 10wt of vanadium incor-poration The morphology particle size and microstructurewere analyzed using high-resolution transmission electronmicroscopy The HRTEM data also confirms the formationof single phase t-ZrO

2 Raman spectra further support and

confirm the crystalline phase as well as the specific bands toshow the modes of vibration in Zr-O system whereas thespecific bands indicate the modes of vibration in Zr-Ti-Oand ZrV

2O7systems The XPS results show that the X-ray

emission of Ti L120572 Zr L

120573215 and O K

120572bands on a common


4

The Raman spectra show the specific bands indicative of themodes of vibration in Zr-V-O system and presence of VO

4

tetrahedra and ZrO6octahedra in the crystal structure XPS

results show that the X-ray emission of V Zr and O bandson a common energy scale indicates that V 2p Zr 3p and O1s states contribute throughout the valence-band region Thecrystallite sizes were found to be in the ranges of sim5ndash10 nmsim2ndash5 nm and sim20ndash50 nm for ZrO

2 ZrTiO

4 and ZrV

2O7

respectively

References

[1] L G Karakchiev T M Zima and N Z Lyakhov ldquoLow-tem-perature synthesis of zirconium titanaterdquo Inorganic Materialsvol 37 no 4 pp 386ndash390 2001

[2] G K Chuah S Jaenicke and B K Pong ldquoThe preparation ofhigh-surface-area zirconia II Influence of precipitating agentand digestion on the morphology and microstructure ofhydrous zirconiardquo Journal of Catalysis vol 175 no 1 pp 80ndash921998

[3] N Q Minh ldquoCeramic fuel cellsrdquo Journal of the American Cera-mic Society vol 76 no 3 pp 563ndash588 1993

[4] A B F Martinson JW Elam J T Hupp andM J Pellin ldquoZnOnanotube based dye-sensitized solar cellsrdquo Nano Letters vol 7no 8 pp 2183ndash2187 2007

[5] E C Subbarao and H S Maiti ldquoOxygen sensors and pumpsrdquoAdvanced Ceramic vol 24 pp 731ndash748 1988

[6] J D Kim S Hana S Kawagoe K Sasaki and T Hata ldquoPrepa-ration of perovskite Pb(Zr Ti)O

3thin-films on YSZ(11)Si(111)

substrates by post-deposition annealingrdquo Thin Solid Films vol385 no 1-2 pp 293ndash297 2001

[7] M Laurent U Schreiner P A Langjahr A E Glazounov andM J Hoffmann ldquoMicrostructural and electrical characteriza-tion of La-doped PZT ceramics prepared by a precursor routerdquoJournal of the European Ceramic Society vol 21 no 10-11 pp1495ndash1498 2001

[8] J T Kim G G Hong and H L Lee ldquoProperties of the powdersof the system Al

2O3-ZrO2-Y2O3prepared by precipitation

methodrdquo Journal of the Korean Ceramic Society vol 25 pp 117ndash124 1988

[9] K Prabakaran S Kannan and S Rajeswari ldquoDevelopment andcharacterisation of zirconia and hydroxyapatite composites fororthopaedic applicationsrdquo Trends in Biomaterials and ArtificialOrgans vol 18 no 2 pp 114ndash116 2005

[10] J L Gole SM Prokes J D Stout O J Glembocki and R YangldquoUnique properties of selectively formed zirconia nanostruc-turesrdquo Advanced Materials vol 18 no 5 pp 664ndash667 2006

[11] L Wang K F Cai Y Y Wang J L Yin H Li and C W ZhouldquoPreparation and characterization of tetragonal-ZrO

2nano-

powders by a molten hydroxides methodrdquo Ceramics Interna-tional vol 35 no 6 pp 2499ndash2501 2009

[12] J Joo T Yu Y W Kim et al ldquoMultigram scale synthesis andcharacterization ofmonodisperse tetragonal zirconia nanocrys-talsrdquo Journal of the American Chemical Society vol 125 no 21pp 6553ndash6557 2003

[13] H Cao X Qiu B Luo et al ldquoSynthesis and room-tempera-ture ultraviolet photoluminescence properties of Zirconiananowiresrdquo Advanced Functional Materials vol 14 no 3 pp243ndash246 2004

[14] S Shukla and S Seal ldquoMechanisms of room temperature meta-stable tetragonal phase stabilisation in zirconiardquo InternationalMaterials Reviews vol 50 no 1 pp 45ndash64 2005

[15] N Vittayakorn ldquoSynthesis and a crystal structural study ofmicrowave dielectric ZirconiumTitanate (ZrTiO

4) powders via

a mixed oxide synthesis routerdquo Journal of Ceramic ProcessingResearch vol 7 no 4 pp 288ndash291 2006

[16] S V Pol V G Pol and A Gedanken ldquoEncapsulating ZnS andZnSe nanocrystals in the carbon shell a RAPET approachrdquoJournal of Physical Chemistry C vol 111 no 36 pp 13309ndash133142007

[17] VDos SantosM Zeni JMHohemberger andC P BergmannldquoPreparation of crystalline ZrTiO4 at low thermal treatmenttemperaturesrdquo Reviews on Advanced Materials Science vol 24no 1-2 pp 44ndash47 2010

[18] B M Reddy P M Sreekanth Y Yamada Q Xu and TKobayashi ldquoSurface characterization of sulfate molybdate andtungstate promoted TiO

2-ZrO2solid acid catalysts by XPS and

other techniquesrdquoApplied Catalysis A vol 228 no 1-2 pp 269ndash278 2002

[19] B M Reddy and A Khan ldquoRecent advances on TiO2-ZrO2

mixed oxides as catalysts and catalyst supportsrdquo CatalysisReviews vol 47 no 2 pp 257ndash296 2005

[20] A Majchrowski J Ebothe E Gondek et al ldquoPhotoinducednonlinear optical effects in the Pr doped BiB3O6 glass nanopar-ticles incorporated into the polymer matricesrdquo Journal of Alloysand Compounds vol 485 no 1-2 pp 29ndash32 2009

[21] Y Djaoued K Ozga A Wojciechowski A H Reshak JRobichaud and I V Kityk ldquoPhotoinduced effects in TiO2


nanocrystalline films with different morphologyrdquo Journal ofAlloys and Compounds vol 508 no 2 pp 599ndash605 2010

[22] A Adamski Z Sojka K Dyrek M Che G Wendt and SAlbrecht ldquoSurface heterogeneity of zirconia-supported V2O5catalysts The link between structure and catalytic properties inoxidative dehydrogenation of propanerdquo Langmuir vol 15 no18 pp 5733ndash5741 1999

[23] E V Kondratenko M Cherian and M Baerns ldquoOxida-tive dehydrogenation of propane over differently structuredvanadia-based catalysts in the presence of O

2and N

2Ordquo Cata-

lysis Today vol 112 no 1ndash4 pp 60ndash63 2006[24] R Sasikala V Sudarsan T Sakuntala J C Sudakar R Naik and

S R Bharadwaj ldquoNanoparticles of vanadia-zirconia catalystssynthesized by polyol-mediated route enhanced selectivity forthe oxidative dehydrogenation of propane to propenerdquo AppliedCatalysis A vol 350 no 2 pp 252ndash258 2008

[25] J J Kingsley andK C Patil ldquoA novel combustion process for thesynthesis of fine particle120572-alumina and related oxidematerialsrdquoMaterials Letters vol 6 no 11-12 pp 427ndash432 1988

[26] S T Aruna and A S Mukasyan ldquoCombustion synthesis andnanomaterialsrdquo Current Opinion in Solid State and MaterialsScience vol 12 no 3-4 pp 44ndash50 2008

[27] S Kumarsrinivasan A Verma and S G Chinnakonda ldquoMolec-ular oxygen-assisted oxidative dehydrogenation of ethylben-zene to styrene with nanocrystalline Ti

1minus119909V119909O2rdquo Green Chem-

istry vol 14 pp 461ndash471 2012[28] B D Cullity Elements of X-Ray Diffraction Addison-Wesley

Reading Mass USA 2nd edition 1978[29] M De and D Kunzru ldquoEffect of calcium and potassium on

V2O5ZrO2catalyst for oxidative dehydrogenation of propane

a comparative studyrdquoCatalysis Letters vol 102 no 3-4 pp 237ndash246 2005

[30] A Khodakov J Yang S Su E Iglesia and A T Bell ldquoStructureand properties of vanadium oxide-zirconia catalysts for pro-pane oxidative dehydrogenationrdquo Journal of Catalysis vol 177no 2 pp 343ndash351 1998

[31] S Biz and M L Occelli ldquoSynthesis and characterization ofmesostructured materialsrdquo Catalysis Reviews vol 40 no 3 pp329ndash407 1998

[32] K S Bartwal S Kar N Kaithwas et al ldquoSynthesis andcharacterization of y

3Al5O12nanocrystalsrdquo Advanced Materials

Research vol 24-25 pp 665ndash670 2007[33] N Kaithwas M Dave S Kar S Verma and K S Bartwal ldquoPre-

paration of NdY3Al5O12

nanocrystals by low temperatureglycol routerdquo Crystal Research and Technology vol 45 no 11pp 1179ndash1182 2010

[34] S Kar S Verma and K S Bartwal ldquoPreparation of Mn dopedLi2B4O7nanoparticles by glass quenchingrdquo Journal of Alloys and

Compounds vol 495 no 1 pp 288ndash291 2010[35] K J Rao and P D Ramesh ldquoUse ofmicrowaves for the synthesis

and processing of materialsrdquo Bulletin of Materials Science vol18 no 4 pp 447ndash465 1995

[36] S Park D W Lee J C Lee and J H Lee ldquoPhotocatalytic silverrecovery using ZnO nanopowders synthesized by modifiedglycine-nitrate processrdquo Journal of the American Ceramic Soci-ety vol 86 no 9 pp 1508ndash1512 2003

[37] B K Kim J W Hahn and K R Han ldquoQuantitative phaseanalysis in tetragonal-rich tetragonalmonoclinic two phase zir-conia by Raman spectroscopyrdquo Journal of Materials ScienceLetters vol 16 no 8 pp 669ndash671 1997

[38] Y K Kim and H M Jang ldquoRaman line-shape analysis of nano-structural evolution in cation-ordered ZrTiO

7-based dielec-

tricsrdquo Solid State Communications vol 127 no 6 pp 433ndash4372003

[39] M A Krebs and R A Condrate ldquoA Raman spectral charac-terization of various crystalline mixtures in the ZrO

2-TiO2and

HfO2-TiO2systemsrdquo Journal of Materials Science Letters vol 7

no 12 pp 1327ndash1330 1988[40] C V Ramana R J Smith O M Hussain M Massot and C

M Julien ldquoSurface analysis of pulsed laser-deposited V2O5thin

films and their lithium intercalated products studied by Ramanspectroscopyrdquo Surface and Interface Analysis vol 37 no 4 pp406ndash411 2005

[41] U L C Hemamala F El-Ghussein D V S Muthu et al ldquoHigh-pressure Raman and infrared study of ZrV

2O7rdquo Solid State

Communications vol 141 no 12 pp 680ndash684 2007[42] A A Lavrentyev B V Gabrelian P N Shkumat et al ldquoElec-

tronic structure of ZrTiO4and HfTiO

4 self-consistent cluster

calculations and X-ray spectroscopy studiesrdquo Journal of Physicsand Chemistry of Solids vol 72 no 2 pp 83ndash89 2011

[43] I F Moulder W E Sticlke P E Sobol and K E BombenHandbook of X-Ray Photoelectron Spectroscopy Edited by JChastian Perkin-Elmer Eden Prairie Minn USA 1992

[44] M Kantcheva ldquoSpectroscopic characterization of vanadium(v)oxo species deposited on zirconiardquo Physical Chemistry ChemicalPhysics vol 2 no 13 pp 3043ndash3048 2000

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


The H+ changes its position to alkoxy group producing aprotonated ROH species which is subsequently eliminatedand metal hydroxide is produced Production of MgO isa typical example The rate of hydrolysis and condensationdepends on (1) electronegativity of the metals atom (2)ability of the metal atom to increase its coordination number(3) steric hindrance of the alkoxy group (4) solvents (5)molecular structure of themetal alkoxide (6) hydrolysis ratioℎ = H

2OMetal and (7) catalyst The rate of hydrolysis of

Ti(OEt)4is 107 times faster than that of Si(OEt)

4 This can be

attributed to the ability of Ti to expand its coordination num-ber from4 to 6 For the same reason the hydrolysis of Sn(OR)

4

is much faster compared to Si(OR)4

Most advanced ceramics are multicomponent systemshaving two or more types of cations in the lattice It is there-fore necessary to prepare gels of high homogeneity in whichcations of various kinds are distributed uniformly at anatomic scale through M-O-M bridges A major problem informing homogeneous multicomponent gel is the unequalhydrolysis and condensation rates of themetal alkoxidesThismay result in chemical inhomogeneities leading to highercrystallization temperatures or even undesired crystallinephases Several approaches have been attempted to overcomethis problem including partial prehydrolysis of less reactiveprecursors matching of hydrolysis rates by chemical modifi-cation with chelating ligands and synthesis of heterometallicalkoxides Conventional self-propagating high temperaturesynthesis (SHS) or condensed phase combustion is associatedwith difficulties like large particle size of nanomaterials andhigh reaction temperature of about 2000∘C Combustion ofmetal oxides by Mg in the presence of NaCl produces smallparticles of metals coated with NaCl Subsequent treatmentof the powder with dilute acid removes MgO impurity Metalcan be recovered by washing the sample with water

Microwave-assisted method of oxide synthesis is gainingpopularity because of its high rate of reaction efficient heattransfer and environmental friendly nature In this processmaterial is directly heated by radiation instead of indirectheating by thermal sources leading to higher temperaturehomogeneity in the reaction mixture In this process of heat-ing microwave radiation interacts with the polar moleculespossessing dipole moment and makes them reorient throughrotation A large number of molecules try to orient togetherresulting in collision and production of heatThusmicrowaveheating is energy conversion method in which electro-magnetic radiation is converted into heat energy ratherthan heat transfer by convection in conventional heat-ing In microwave-assisted solution combustion synthesis(MWSCS) an aqueous solution of metal nitrate (oxidant) andfuel (urea citric acid) is subjected to a microwave heatingfor few minutes to obtain a viscous gel which on drying andcalcination produces the metal oxidemixedmetal oxideThesolution combustion method seems to be modification ofthe conventional oxalate method which is used for preparingmetal oxides and supported metal oxides The citrate gel de-composition process is better known as a thermally inducedanionic oxidation-reduction reaction In the process chelatesare formed between metal ions facilitating atomic scale dis-tribution of ions in a polymer network Heating of this resin

causes the breakdown of the polymer and a solid amorphousprecursor material is finally obtained On subsequent heatingbetween 500 and 900∘C the cations are oxidized to form therespective metal oxides Microwave-assisted MVSCS tech-nique can be used for preparingmaterials or catalysts catalystsupport fuel cells capacitors Li-ion rechargeable batteriesdye-sensitized solar cells solid oxide fuel cells (SOFC) anddirect methanol fuel cells (DMFCs)

The development of zirconia (ZrO2) nanoparticles has

attracted much attention due to their multifunctional char-acteristics Nanoparticles have been recognized to havepotential in the area of photonic applications It has severalapplications such as solid oxide fuel cell biosensors H

2gas

storagematerial oxygen sensor catalyst and catalyst support[2ndash5] In addition zirconia is used as piezoelectric materialelectrooptic material and dielectric material [6ndash8] It is alsoused as support to disperse various noble and transition met-als for distinct catalytic applications Zirconia is a well-knownsolid acid catalyst and an n-type semiconductor materialZrO2is also used as toughening ceramics in thighbone and

oral planting [9] The existence of metastable tetragonal (t-ZrO2) at low temperature has been synthesized by several

methods Some of the methodologies such as oxidation ofZrCl2by molecular oxygen [10] molten hydroxides method

[11] nonhydrolytic sol-gel reaction between isopropoxideand ZrCl

4[12] and sol-gel template technique [13 14] are

developed to prepare nanocrystalline ZrO2

The traditional preparation of zirconium titanate (ZrTiO4)

ceramic is based on solid-state reaction between the TiO2

and ZrO2powders at high temperatures (above 1400∘C)

[15] In order to improve the functional properties of theceramic material heat treatments are generally necessarywhich consume high amount of energy Chemical methodbased on Coprecipitation of the reactive precursors wasdeveloped to prepare powders with a high purity and lowtreatment cost after reaction [16] Low temperature synthesisof zirconium titanate has been reported by Karakchiev et al[1] and Dos Santos et al [17] Zirconium titanate possessinga layered wolframite-type structure (ABO

4) with space group

P2a finds applications asmicrowave components As catalystand catalyst supports ZrTiO

4is employed for a wide variety

of catalytic applications both in liquid and gaseous phases [1819] Recently it has been reported that the oxide nanoparticlesare promising for photonics and their monodispersion andappropriate contact with the surrounding medium are verycrucial parameters [20 21]

Vanadium incorporated zirconia (V2O5-ZrO2) is ameso-

porous material and is very useful catalyst Nanoporousmaterials consist of a regular organic or inorganic frameworksupporting a regular porous structure A mesoporous mate-rial is a material containing pores with diameters between2 and 50 nm The 120572-phase (cubic) of ZrV

2O7is the stable

structure at ambient conditions It consists of ZrO6octahedra

whose corners share their oxygen atomswithVO4tetrahedra

Vanadiumoxide catalysts supported on differentmetal oxidesare widely used inmany industrial reactions such as selectivecatalytic reduction of NO with NH

3 ammoxidation of alkyl

aromatics and the selective oxidation of hydrocarbons Prop-erties of supported vanadium catalysts depend on a variety



2 MgO and HfO

2[23 24] Among



2




2has been per-


4particles were








2O4H2)







2sdot8H2O 295 g of


4



3) is mixed









4and





20 40 60 80

220

101

110 21

1

112

Inte

nsity

(au

)ZrO2

2120579

(a)

20 30 40 50 60 70

ZT1202

22202

2

200

311

220

130

002

111

110

Inte

nsity

(au

)

ZT2

2120579

(b)

20 30 40 50 60 70

311220

00211

1

2120579

ZrO2

400 ∘C

600 ∘C

800 ∘C

Inte

nsity

(au

)

(c)



2O7



72and Cu 2p

32







2) were prepared







2O5con-




120572



0 05 1 15 2 25 3

(B)

(D) (C)

(A)

Inte

nsity

(au

)

(A) ZV2 (B) ZV5

(C) ZV8 (D) ZV10

2120579






2(JCPDF






119863 =09120582

(120573 cos 120579) (3)











4at 2120579 values 35 37










2







(a) (b)



(a) (b)












4(ZT2) is shown



(a) (b)












2and ZrTiO




Γ = 1198601119892+ 21198611119892+ 3119864119892 (4)

In 1198601119892








1119892



2 In addition







119892 51198611119892 41198612119892


0 1000 2000

Inte

nsity

(au

)

146

470259

123

382

(B)

(A)643

(A) ZrO2 600 ∘C

(B) ZrO2 800 ∘C


(a)

200 400 600 800 1000 1200

Inte

nsity

(au

)

ZT1


(b)

200 400 600 800 1000 1200

Inte

nsity

(au

)

ZT2


(c)

200 400 600 800 1000 1200

(C)(B)

(A)


(A) ZV10 400∘C

(B) ZV10 600∘C

(C) ZV10 800∘C

Inte

nsity

(au

)

(d)



51198613119892











2O7crystals




4tetrahedra


0 200 400 600 800 1000 1200

Zr 3p

Inte

nsity

(au

)

BE (eV)

ZrTiO4

Ti 2pTi 2s

O KLLO 1s

Zr 3p

C 1S

Zr 3d

Zr 4p

(a)

Inte

nsity

(au

)

0 200 400 600 800 1000 1200BE (eV)

ZrV2O7

O KLL

O 1s

Zr 3pC 1SZr 3d

Zr 4p

(b)












2O5ZrO2




4



4(ZT2)






4


52 Zr 3p

32 and Ti 2p









32and indicates the






32and Zr 3p

12 respectively

The binding


4 Conclusion


2and ZrTiO







2O7and formation






120573215 and O K



4


4



2 ZrTiO

4 and ZrV

2O7

respectively

References
















2nano-






4) powders via















2and N

2Ordquo Cata-
























7-based dielec-



2-TiO2and




















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





2 MgO and HfO

2[23 24] Among



2




2has been per-


4particles were








2O4H2)







2sdot8H2O 295 g of


4



3) is mixed









4and





20 40 60 80

220

101

110 21

1

112

Inte

nsity

(au

)ZrO2

2120579

(a)

20 30 40 50 60 70

ZT1202

22202

2

200

311

220

130

002

111

110

Inte

nsity

(au

)

ZT2

2120579

(b)

20 30 40 50 60 70

311220

00211

1

2120579

ZrO2

400 ∘C

600 ∘C

800 ∘C

Inte

nsity

(au

)

(c)



2O7



72and Cu 2p

32







2) were prepared







2O5con-




120572



0 05 1 15 2 25 3

(B)

(D) (C)

(A)

Inte

nsity

(au

)

(A) ZV2 (B) ZV5

(C) ZV8 (D) ZV10

2120579






2(JCPDF






119863 =09120582

(120573 cos 120579) (3)











4at 2120579 values 35 37










2







(a) (b)



(a) (b)












4(ZT2) is shown



(a) (b)












2and ZrTiO




Γ = 1198601119892+ 21198611119892+ 3119864119892 (4)

In 1198601119892








1119892



2 In addition







119892 51198611119892 41198612119892


0 1000 2000

Inte

nsity

(au

)

146

470259

123

382

(B)

(A)643

(A) ZrO2 600 ∘C

(B) ZrO2 800 ∘C


(a)

200 400 600 800 1000 1200

Inte

nsity

(au

)

ZT1


(b)

200 400 600 800 1000 1200

Inte

nsity

(au

)

ZT2


(c)

200 400 600 800 1000 1200

(C)(B)

(A)


(A) ZV10 400∘C

(B) ZV10 600∘C

(C) ZV10 800∘C

Inte

nsity

(au

)

(d)



51198613119892











2O7crystals




4tetrahedra


0 200 400 600 800 1000 1200

Zr 3p

Inte

nsity

(au

)

BE (eV)

ZrTiO4

Ti 2pTi 2s

O KLLO 1s

Zr 3p

C 1S

Zr 3d

Zr 4p

(a)

Inte

nsity

(au

)

0 200 400 600 800 1000 1200BE (eV)

ZrV2O7

O KLL

O 1s

Zr 3pC 1SZr 3d

Zr 4p

(b)












2O5ZrO2




4



4(ZT2)






4


52 Zr 3p

32 and Ti 2p









32and indicates the






32and Zr 3p

12 respectively

The binding


4 Conclusion


2and ZrTiO







2O7and formation






120573215 and O K



4


4



2 ZrTiO

4 and ZrV

2O7

respectively

References
















2nano-






4) powders via















2and N

2Ordquo Cata-
























7-based dielec-



2-TiO2and




















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




20 40 60 80

220

101

110 21

1

112

Inte

nsity

(au

)ZrO2

2120579

(a)

20 30 40 50 60 70

ZT1202

22202

2

200

311

220

130

002

111

110

Inte

nsity

(au

)

ZT2

2120579

(b)

20 30 40 50 60 70

311220

00211

1

2120579

ZrO2

400 ∘C

600 ∘C

800 ∘C

Inte

nsity

(au

)

(c)



2O7



72and Cu 2p

32







2) were prepared







2O5con-




120572



0 05 1 15 2 25 3

(B)

(D) (C)

(A)

Inte

nsity

(au

)

(A) ZV2 (B) ZV5

(C) ZV8 (D) ZV10

2120579






2(JCPDF






119863 =09120582

(120573 cos 120579) (3)











4at 2120579 values 35 37










2







(a) (b)



(a) (b)












4(ZT2) is shown



(a) (b)












2and ZrTiO




Γ = 1198601119892+ 21198611119892+ 3119864119892 (4)

In 1198601119892








1119892



2 In addition







119892 51198611119892 41198612119892


0 1000 2000

Inte

nsity

(au

)

146

470259

123

382

(B)

(A)643

(A) ZrO2 600 ∘C

(B) ZrO2 800 ∘C


(a)

200 400 600 800 1000 1200

Inte

nsity

(au

)

ZT1


(b)

200 400 600 800 1000 1200

Inte

nsity

(au

)

ZT2


(c)

200 400 600 800 1000 1200

(C)(B)

(A)


(A) ZV10 400∘C

(B) ZV10 600∘C

(C) ZV10 800∘C

Inte

nsity

(au

)

(d)



51198613119892











2O7crystals




4tetrahedra


0 200 400 600 800 1000 1200

Zr 3p

Inte

nsity

(au

)

BE (eV)

ZrTiO4

Ti 2pTi 2s

O KLLO 1s

Zr 3p

C 1S

Zr 3d

Zr 4p

(a)

Inte

nsity

(au

)

0 200 400 600 800 1000 1200BE (eV)

ZrV2O7

O KLL

O 1s

Zr 3pC 1SZr 3d

Zr 4p

(b)












2O5ZrO2




4



4(ZT2)






4


52 Zr 3p

32 and Ti 2p









32and indicates the






32and Zr 3p

12 respectively

The binding


4 Conclusion


2and ZrTiO







2O7and formation






120573215 and O K



4


4



2 ZrTiO

4 and ZrV

2O7

respectively

References
















2nano-






4) powders via















2and N

2Ordquo Cata-
























7-based dielec-



2-TiO2and




















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




0 05 1 15 2 25 3

(B)

(D) (C)

(A)

Inte

nsity

(au

)

(A) ZV2 (B) ZV5

(C) ZV8 (D) ZV10

2120579






2(JCPDF






119863 =09120582

(120573 cos 120579) (3)











4at 2120579 values 35 37










2







(a) (b)



(a) (b)












4(ZT2) is shown



(a) (b)












2and ZrTiO




Γ = 1198601119892+ 21198611119892+ 3119864119892 (4)

In 1198601119892








1119892



2 In addition







119892 51198611119892 41198612119892


0 1000 2000

Inte

nsity

(au

)

146

470259

123

382

(B)

(A)643

(A) ZrO2 600 ∘C

(B) ZrO2 800 ∘C


(a)

200 400 600 800 1000 1200

Inte

nsity

(au

)

ZT1


(b)

200 400 600 800 1000 1200

Inte

nsity

(au

)

ZT2


(c)

200 400 600 800 1000 1200

(C)(B)

(A)


(A) ZV10 400∘C

(B) ZV10 600∘C

(C) ZV10 800∘C

Inte

nsity

(au

)

(d)



51198613119892











2O7crystals




4tetrahedra


0 200 400 600 800 1000 1200

Zr 3p

Inte

nsity

(au

)

BE (eV)

ZrTiO4

Ti 2pTi 2s

O KLLO 1s

Zr 3p

C 1S

Zr 3d

Zr 4p

(a)

Inte

nsity

(au

)

0 200 400 600 800 1000 1200BE (eV)

ZrV2O7

O KLL

O 1s

Zr 3pC 1SZr 3d

Zr 4p

(b)












2O5ZrO2




4



4(ZT2)






4


52 Zr 3p

32 and Ti 2p









32and indicates the






32and Zr 3p

12 respectively

The binding


4 Conclusion


2and ZrTiO







2O7and formation






120573215 and O K



4


4



2 ZrTiO

4 and ZrV

2O7

respectively

References
















2nano-






4) powders via















2and N

2Ordquo Cata-
























7-based dielec-



2-TiO2and




















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)



(a) (b)












4(ZT2) is shown



(a) (b)












2and ZrTiO




Γ = 1198601119892+ 21198611119892+ 3119864119892 (4)

In 1198601119892








1119892



2 In addition







119892 51198611119892 41198612119892


0 1000 2000

Inte

nsity

(au

)

146

470259

123

382

(B)

(A)643

(A) ZrO2 600 ∘C

(B) ZrO2 800 ∘C


(a)

200 400 600 800 1000 1200

Inte

nsity

(au

)

ZT1


(b)

200 400 600 800 1000 1200

Inte

nsity

(au

)

ZT2


(c)

200 400 600 800 1000 1200

(C)(B)

(A)


(A) ZV10 400∘C

(B) ZV10 600∘C

(C) ZV10 800∘C

Inte

nsity

(au

)

(d)



51198613119892











2O7crystals




4tetrahedra


0 200 400 600 800 1000 1200

Zr 3p

Inte

nsity

(au

)

BE (eV)

ZrTiO4

Ti 2pTi 2s

O KLLO 1s

Zr 3p

C 1S

Zr 3d

Zr 4p

(a)

Inte

nsity

(au

)

0 200 400 600 800 1000 1200BE (eV)

ZrV2O7

O KLL

O 1s

Zr 3pC 1SZr 3d

Zr 4p

(b)












2O5ZrO2




4



4(ZT2)






4


52 Zr 3p

32 and Ti 2p









32and indicates the






32and Zr 3p

12 respectively

The binding


4 Conclusion


2and ZrTiO







2O7and formation






120573215 and O K



4


4



2 ZrTiO

4 and ZrV

2O7

respectively

References
















2nano-






4) powders via















2and N

2Ordquo Cata-
























7-based dielec-



2-TiO2and




















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)












2and ZrTiO




Γ = 1198601119892+ 21198611119892+ 3119864119892 (4)

In 1198601119892








1119892



2 In addition







119892 51198611119892 41198612119892


0 1000 2000

Inte

nsity

(au

)

146

470259

123

382

(B)

(A)643

(A) ZrO2 600 ∘C

(B) ZrO2 800 ∘C


(a)

200 400 600 800 1000 1200

Inte

nsity

(au

)

ZT1


(b)

200 400 600 800 1000 1200

Inte

nsity

(au

)

ZT2


(c)

200 400 600 800 1000 1200

(C)(B)

(A)


(A) ZV10 400∘C

(B) ZV10 600∘C

(C) ZV10 800∘C

Inte

nsity

(au

)

(d)



51198613119892











2O7crystals




4tetrahedra


0 200 400 600 800 1000 1200

Zr 3p

Inte

nsity

(au

)

BE (eV)

ZrTiO4

Ti 2pTi 2s

O KLLO 1s

Zr 3p

C 1S

Zr 3d

Zr 4p

(a)

Inte

nsity

(au

)

0 200 400 600 800 1000 1200BE (eV)

ZrV2O7

O KLL

O 1s

Zr 3pC 1SZr 3d

Zr 4p

(b)












2O5ZrO2




4



4(ZT2)






4


52 Zr 3p

32 and Ti 2p









32and indicates the






32and Zr 3p

12 respectively

The binding


4 Conclusion


2and ZrTiO







2O7and formation






120573215 and O K



4


4



2 ZrTiO

4 and ZrV

2O7

respectively

References
















2nano-






4) powders via















2and N

2Ordquo Cata-
























7-based dielec-



2-TiO2and




















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




0 1000 2000

Inte

nsity

(au

)

146

470259

123

382

(B)

(A)643

(A) ZrO2 600 ∘C

(B) ZrO2 800 ∘C


(a)

200 400 600 800 1000 1200

Inte

nsity

(au

)

ZT1


(b)

200 400 600 800 1000 1200

Inte

nsity

(au

)

ZT2


(c)

200 400 600 800 1000 1200

(C)(B)

(A)


(A) ZV10 400∘C

(B) ZV10 600∘C

(C) ZV10 800∘C

Inte

nsity

(au

)

(d)



51198613119892











2O7crystals




4tetrahedra


0 200 400 600 800 1000 1200

Zr 3p

Inte

nsity

(au

)

BE (eV)

ZrTiO4

Ti 2pTi 2s

O KLLO 1s

Zr 3p

C 1S

Zr 3d

Zr 4p

(a)

Inte

nsity

(au

)

0 200 400 600 800 1000 1200BE (eV)

ZrV2O7

O KLL

O 1s

Zr 3pC 1SZr 3d

Zr 4p

(b)












2O5ZrO2




4



4(ZT2)






4


52 Zr 3p

32 and Ti 2p









32and indicates the






32and Zr 3p

12 respectively

The binding


4 Conclusion


2and ZrTiO







2O7and formation






120573215 and O K



4


4



2 ZrTiO

4 and ZrV

2O7

respectively

References
















2nano-






4) powders via















2and N

2Ordquo Cata-
























7-based dielec-



2-TiO2and




















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




0 200 400 600 800 1000 1200

Zr 3p

Inte

nsity

(au

)

BE (eV)

ZrTiO4

Ti 2pTi 2s

O KLLO 1s

Zr 3p

C 1S

Zr 3d

Zr 4p

(a)

Inte

nsity

(au

)

0 200 400 600 800 1000 1200BE (eV)

ZrV2O7

O KLL

O 1s

Zr 3pC 1SZr 3d

Zr 4p

(b)












2O5ZrO2




4



4(ZT2)






4


52 Zr 3p

32 and Ti 2p









32and indicates the






32and Zr 3p

12 respectively

The binding


4 Conclusion


2and ZrTiO







2O7and formation






120573215 and O K



4


4



2 ZrTiO

4 and ZrV

2O7

respectively

References
















2nano-






4) powders via















2and N

2Ordquo Cata-
























7-based dielec-



2-TiO2and




















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





32and Zr 3p

12 respectively

The binding


4 Conclusion


2and ZrTiO







2O7and formation






120573215 and O K



4


4



2 ZrTiO

4 and ZrV

2O7

respectively

References
















2nano-






4) powders via















2and N

2Ordquo Cata-
























7-based dielec-



2-TiO2and




















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials







2and N

2Ordquo Cata-
























7-based dielec-



2-TiO2and




















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



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Research Article Microwave-Assisted Synthesis of Mixed ...downloads.hindawi.com/journals/jnp/2013/737831.pdf · Research Article Microwave-Assisted Synthesis of Mixed Metal-Oxide