ISSN 0012�5008, Doklady Chemistry, 2012, Vol. 442, Part 2, pp. 40–41. © Pleiades Publishing, Ltd., 2012.Original Russian Text © E.P. Lokshin, T.A. Sedneva, V.T. Kalinnikov, 2012, published in Doklady Akademii Nauk, 2012, Vol. 442, No. 5, pp. 634–635.

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Bulk electrical conductivity is an important char�acteristic of powder materials promising as, e.g., com�ponents of anodes or cathodes of lithium ion batteries.Often, practically useful results can only be achievedusing nanosized powders. However, estimating theirelectrical conductivity is particularly difficult becauseit is impossible to determine the total particle contactarea and separate the contributions of the bulk andsurface conductivities. The surface conductivity isadditionally affected by surface�sorbed impurities(first of all, atmospheric moisture), the content ofwhich depends on many factors, including the specificfree surface area of the powder, i.e., on its particle size.

Therefore, for measuring the bulk conductivity,powders are preliminarily compacted or sintered.However, compaction does not resolve the above prob�lems, whereas sintering often changes the material orphase composition of the material, preventing fromreliably estimating the electrophysical properties ofthe initial product. Therefore, it was necessary todevelop a method for estimating the bulk conductivityof dispersed solid particles, in particular, nanosizedpowders.

We proposed an indirect method for estimating theelectrical conductivity of ultrafine powders of a num�ber of materials from their photocatalytic properties,namely, the spectral threshold of photocatalytic sus�ceptibility and the photocatalytic activity.

The method is based on the assumption that bandgap reduction and an increase in the photocatalyticactivity of materials of similar chemical compositionsare indicative of an increase in their bulk conductivity.

The photocatalytic activities of various materialscan be compared by comparing the rates of a certainphotocatalytic reaction performed under similar con�ditions (at equal initial concentrations of reactants and

a photocatalyst in the reaction system, identicalhydrodynamic conditions of contact of the photocat�alyst and a solution containing the reactants, and thesame intensities and spectral compositions of the illu�minating light). Although such an approach allows noquantitative estimation of the electrical conductivity,for materials of a certain type, it enables the compara�tive evaluation of the electrical conductivity of nano�sized powders.

The reaction was performed as follows. Weighedsamples of nanosized powders of materials under studywere placed in equal volumes of a solution containinga colored organic substance (in our experiments, thecolor indicators ferroin and/or methylene blue) at agiven concentration. Glass or polyethylene vessels ofidentical shapes were shaken on an LAB�PU�01shaker while being illuminated by the light of a chosensource (as a rule, a 100 W incandescent lamp). Theilluminating light was corrected using a set of samplesof colored optical glasses—light filters with knownvalues of the radiation transmission threshold [1].

The change in the color intensity (decolorization)after a while, which characterizes the photocatalyticactivity of the material, was measured with an FEK�56PM photocolorimeter. The indicator decomposi�tion efficiency A (%) as a measure of photocatalyticactivity was calculated by the equation

А = [(c0 – c)/c0] × 100, (1)

where c0 and c are the initial and residual concentra�tions of the color indicator in the solution, respec�tively.

By changing the light filters, we increased the wave�length of the light illuminating the photocatalyst andestimated the maximal wavelength (spectral thresholdof photocatalytic susceptibility), at which, all otherconditions being equal, the photocatalytic activity ofthe powder began to noticeably decrease. We typicallyused the light filters ZhS�11 (λ = 420 nm), KS�17(λ = 670 nm), and IKS�1 (λ = 900 nm).

The band gap corresponding to the maximum stud�ied wavelength that ensured the efficient photocata�

CHEMISTRY

Estimation of the Electrical Conductivity of Nanosized PowdersE. P. Lokshin, T. A. Sedneva, and Academician V. T. Kalinnikov

Received February 25, 2011

DOI: 10.1134/S001250081202005X

Tananaev Institute of Chemistry and Technology of Rare Elements and Mineral Raw Materials, Kola Research Center, Russian Academy of Sciences, Akademgorodok 26a, Apatity, Murmansk oblast, 184209 Russia

DOKLADY CHEMISTRY Vol. 442 Part 2 2012

ESTIMATION OF THE ELECTRICAL CONDUCTIVITY OF NANOSIZED POWDERS 41

lytic decomposition of the substance was calculated bythe equation [2]

(2)

where Е is the band gap, λ is the wavelength at thespectral threshold of photocatalytic susceptibility, h isthe Planck constant, and с is the speed of light.

The method was used, in particular, for estimatingthe electrical conductivity of nanosized powders oftitania doped with Fe3+, Nb5+, or W6+ cations in highconcentrations. The estimation was made for choos�ing the compositions and synthesis conditions of tita�nia�based materials promising as anodic materials oflithium ion batteries. As noted above, the high electri�cal conductivity of such materials is one of the funda�mental properties that ensure their use for this pur�pose.

According to the obtained experimental data, wechose materials that had high photocatalytic activitywhile being illuminated by the light with a wavelengthof no less than 900 nm (Е ≤ 1.38 eV) and also selected

reference materials with higher Е and/or lower photo�catalytic activity. Performed at the Chair of Technol�ogy of Electrochemical Plants, St. Petersburg StateTechnological University, St. Petersburg, Russia,comparative tests of the chosen materials as anodicmaterials of lithium ion batteries showed their highspecific capacitance (up to 470 mA h g–1 [3]), itsdecrease with worsening the photocatalytic propertiesof the materials, and the unsuitability of materials withЕ ≈ 3 eV (undoped titania).

REFERENCES

1. Veinberg, I.I., Katalog tsvetnogo stekla (Catalog of Col�ored Glass), Moscow: Mashinostroenie, 1967.

2. Pavlov, P.V. and Khokhlov, A.R., Fizika tverdogo tela(Solid State Physics), Moscow: Vysshaya shkola, 2000.

3. Kir’yanov, B.V., Kudryavtsev, E.N., Agafonov, D.V.,et al., Abstracts of papers, Mezhdunar. konf. “Teoriya ipraktika sovremennykh elektrokhimicheskikh proizvod�stv” (Int. Conf. “Theory and Practice of Modern Elec�trochemical Productions”), St. Petersburg: SPb. Gos.Technol. Inst., 2010, vol. 2, pp. 90–91.

=λ

,hcE