Journal of Crystal Growth 233 (2001) 774–778

The synthesis of SbSI rodlike crystals with studded pyramids

Qing Yang, Kaibin Tang*, Chunrui Wang, Bin Hai, Guozhen Shen, Changhua An,Chunjuan Zhang, Yitai Qian1

Structure Research Laboratory and Department of Chemistry, University of Science and Technology of China, Hefei,

Anhui 230026, People’s Republic of China

Received 27 March 2001; accepted 26 July 2001

Communicated by L.F. Schneemeyer

Abstract

The SbSI rodlike crystals with studded pyramids were synthesized from the reaction among antimony trichloride,thiourea, and excessive sodium iodide under moderate hydrothermal conditions at 2001C. The final products werecharacterized by XRD, SEM, XPS, and elemental analysis. The SEM images showed the SbSI rodlike crystals are

inserted some octahedrons on the surfaces of the rods. Typically, the structure is 3–4mm in length, 8–10 mm in diameterfor a singular crystal. The size of the pyramids on the surface is about 10mm in height and the length of hemline is6–12mm. r 2001 Elsevier Science B.V. All rights reserved.

PACS: 61.10.N; 61.66.F; 81.10

Keywords: A1. X-ray diffraction; A2. Hydrothermal crystal growth; B1. Inorganic compounds

1. Introduction

SbSI and its related chalcogenide halide com-pounds may have semiconducting properties pre-dicted by Mooser and Pearson in 1958 [1]. Thephotoconductivity [2] of SbSI was found in 1960and its 2.12 eV band gap [3] exhibits abnormallylarge temperature-coefficients for solar cell re-searches. The discovery of its ferroelectricity [4]was the breakthrough and it has drawn a greatdeal of attention on its further researches [5–7].

Since SbSI has been synthesized by Donges [7]in 1950, a lot of techniques have been used toproduce SbSI crystals. Nittsche et al. [2] employedthe melting growth route with the Bridgman–Stockbarger technique to produce parallel bundlesof fibrous crystals. Kern [6] and Belyaev et al. [8]have used vapor phase growth to produce milli-meter size crystals in a vacuum between 3601C and4101C. At the same time, hydrothermal growthmethod [9,10] has also been used to synthesizeSbSI. Popolitov and Litvin [9] conducted experi-ments under hydrothermal conditions at 250–3001C, and 400–600 ata from H2S solution at pH5–6. Rau and Rabenau [10] used a quartz ampoulewith an external pressure of 2400 ata and a filling9M HI solution and at 250–4901C. Nassau et al.

*Corresponding authors. Fax: +86-551-360-1600.

E-mail address: kbtang@ustc.edu.cn (K. Tang).1Also Corresponding author. Fax: +86-551-360-1600.

0022-0248/01/$ - see front matter r 2001 Elsevier Science B.V. All rights reserved.

PII: S 0 0 2 2 - 0 2 4 8 ( 0 1 ) 0 1 6 4 3 - 8

[11] used a modified flux technique by using excessSbI3 as the solvent and circumventing the inherentgrowth anisotropy to grow large SbSI crystals. Inthe present contribution, we synthesized SbSIcrystals under a relative mild hydrothermal reac-tion at 2001C and no more than 16 ata [12] fromSbCl3, (NH2)2CS and a rather excess feedstock ofNaI in aqueous solution.

2. Experimental section

2.1. Synthesis

In a typical experiment, an appropriate amountof analytically pure SbCl3 (0.80 g), and (NH2)2CSand NaI (with a molar ratio of 1.05 : 1 : 3B5) wasadded into the Teflon-lined stainless steel auto-clave, which was filled up to 90% of the totalvolume (50ml) with distilled water. When thereactants were mixed, the orange red in color wasseen in solution, which indicated that amorphousSb2S3 [13] and the SbCl3-thiourea complex [14]were formed, and in succession the color changedto purple red, which showed somewhat amountSbI3 was formed [15]. The autoclave was main-tained at 2001C for 20–40 h and rapidly cooled toroom temperature, and then allowed to stand for20–30 h at room temperature naturally. Theprecipitate was washed with carbon disulfide,ether, distilled water and absolute alcohol sequen-tially. After drying in a vacuum at 60–701C for 4 h,the limpid rodlike crystals in purple red color wereobtained.

2.2. Characterization

The products were determined by X-ray diffrac-tion (XRD) operated on a MXP18AHF (MACScience Co Ltd.) rotation anode X-ray diffracto-meter with graphite monochromatized CuKa

radiation (l ¼ 1:54056 (A). The scanning rate of0.0201/s was applied to record the patterns in the2y range of 10–701. The morphology of thecrystals was observed by scanning electron micro-scopy (SEM), which was performed on an X-650scanning electron microanalyzer. X-ray photoelec-tron spectra (XPS), collected on an ESCALAB

MK II X-ray photoelectron spectrometer usingnonmonochromatized Mg Ka X-ray as the excita-tion source, confirms the formation of SbSI.Element analysis for the composition of thesamples was done by ICP-AES, which was carriedon an Atomscan Advantage (Thermo Jarrell AshCorporation). Diffuse reflection (DR) spectra ofthe samples were measured on a Shimadzu UV-240 recording spectrophotometer scanning from400 to 800 nm at room temperature.

3. Results and discussion

Fig. 1 is the XRD patterns of the polycrystallinepowder ground from the products. The XRDspectra could be indexed to the orthorhombic SbSIphase with lattice parameters a ¼ 8:525; b ¼10:131; c ¼ 4:090 (A, which are in agreement withthe reported data for SbSI (JCPDS Card File,21–50). No other characteristic peaks of impuritiessuch as Sb2S3, SbOI, or S were observed.The SEM image of as-grown SbSI crystals is

showed in Fig. 2. It can be seen that themorphologies of SbSI crystals are rodlike structurewith studded pyramids. Typically, this structure is3–4mm in length, 8–10 mm in diameter for asingular crystal. The studded pyramids locating onthe surfaces of the rodlike crystals are denselyscattered. The size of the pyramids is about 10 mmin height and the length of hemline is 6–12 mm.

Fig. 1. The powder XRD patterns ground from the SbSI

rodlike crystals.

Q. Yang et al. / Journal of Crystal Growth 233 (2001) 774–778 775

A typical XPS survey spectrum of the sampleshows the existence of the Sb, S and I (Fig. 3). Theclose-up spectra of Sb, S, and I give bindingenergies of 529.05 161.80, 618.65 eV for Sb 3d5/2, S2p, and I 3d5/2, repectively. No obvious peaks forO or element S (164.05 eV) were observed. Directelemental analysis for the composition was em-ployed by ICP-AES and it gave that the molarratio of Sb : SL : I is 1.000 : 0.976 : 1.027. Theresults revealed the obtained rodlike crystals arestoichiometric.

In our hydrothermal synthetic route, the SbSIrodlike crystals with studded pyramids have beenachieved from the reaction among antimonytrichloride, thiourea, and excessive sodium iodideat relative low temperature.In the procedures, the following reactions or

equilibria existed in reaction system.

SbCl3þðNH2Þ2CS-SbCl3-ðNH2Þ2CS complex;

ð1Þ

ðNH2Þ2CSþ 2H2O-H2Sþ CO2þ2NH3; ð2Þ

2SbCl3þ3H2S-Sb2S3þ6HCl; ð3Þ

SbCl3þ3NaI-SbI3þ3NaCl; ð4Þ

Sb2S3þSbI3-3SbSI: ð5Þ

Rodlike Sb2S3 nanocrystallites have beensynthesized from a single source precursor anti-mony-thiourea complex in methanol, through asolvothermal decomposition process [16]. In thepresent aqueous solution, SbCl3 thiourea complex[14] could be similarly formed when antimonychloride mixed with thiourea in the procedures.With the hydrolyzing of thiourea, the SbCl3thiourea complex may change to orange redamorphous Sb2S3 [13] according to (3). The higherpressure of the environment is favorable for theformation of Sb2S3 with rodlike morphologies [16].When the reactive temperature was evaluated inthe closed vessel with a relative high pressure,reaction (3) occurred rapidly and rodlike Sb2S3crystals were formed. In the meantime, SbCl3acted with NaI to form SbI3 under hydrothermalconditions in aqueous solution according toequilibrium (4) [15]. SbSI could be proposed fromreaction (5) in the process, which is similar tothe reported sinter route [17]. The formation of therodlike SbSI crystals may be achieved from theinherent growth anisotropy [11] of the orthorhom-bic phase SbSI and the template effect of the earlyformed Sb2S3 rodlike crystallites. The studdedpyramids on the surfaces of the rodlike crystals aresome octahedrons. From SEM images, we canobserve the octahedrons are inserted on thesurface of the rodlike morphologic SbSI, so wethink the rods formed earlier than the octahedronsdid in the crystal growth process. The octahedrons

Fig. 2. SEM image of the as-produced SbSI rodlike crystals.

Fig. 3. The survey spectrum of the product from XPS analysis.

Q. Yang et al. / Journal of Crystal Growth 233 (2001) 774–778776

may be proposed to form from the nucleus on thesurface of the rods. At 2001C, relative lowtemperature, the rods may have some defects onthe surfaces, which could form new crystalnucleus. Once the nucleus formed, the studdedoctahedrons can grow in succession.The reaction temperature and the reaction time

were also studied. In the present process, thereaction temperature cannot be less than 1801Cand the reaction time cannot be shorter than 5 h.If the reactive temperature was lower than1601C, SbSI was difficult to obtain and theproduced samples are only Sb2S3 mixed withhydrolysates in red solution. Similarly, if thereactive time was less than 2 h, SbSI was alsodifficult to obtain. The cooling process alsoaffected the formation of the SbSI crystals. Theautoclave should be rapidly cooled to the roomtemperature after reaction.In order to get some effective information on the

optical properties of the as-prepared SbSI crystals;we measured DR spectra of the samples scanningfrom 400 to 800 nm, shown in Fig. 4. The diffusereflectance sharply descends from about 700 nm.The band gap of the crystalline products is about2.14 eV, which is near to the band gap of thereported value [3].

4. Summary

In conclusion, SbSI rodlike crystals withstudded pyramids were achieved from the reactionamong antimony trichloride, thiourea, and exces-sive sodium iodide under hydrothermal conditionsat 2001C for 20–40 h. The synthetic conditions inthe present route are moderate comparing with thereported synthetic routes. SEM images showed thesample had rodlike morphologies with pyramidson the surfaces of the crystals. The interestingmorphologies of the crystals may be caused by themoderate conditions. It is believed that theseparticular crystals with interesting morphologiesshould be expected to have novel properties.

Acknowledgements

Financial support of this work by the NationalNatural Science Foundation of China and the 973Projects of China is gratefully acknowledged. Weare indebted to Prof. G.E. Zhou, J.X. Wu andF.Q. Li for their valuable comments.

References

[1] E. Mooser, W.B. Pearson, J. Phys. Chem. Solids 7 (1958)

65.

[2] R. Nitsche, W.J. Merz, J. Phys. Chem. Solids 13 (1960)

154.

[3] J.F. Alward, C.Y. Fong, M. El Batanouny, F. Wooten,

Solid State Commun. 25 (1978) 307.

[4] E. Fatuzzo, G. Harbeke, W.J. Merz, R. Nitsche, H.

Roetschi, W. Ruppel, Phys. Rev. 127 (1962) 2034.

[5] Y. Masuda, K. Sakata, S. Hasegawa, G. Ohara, M. Wada,

M. Nishizawa, Jpn. J. Appl. Phys. 8 (1969) 692.

[6] R. Kern, J. Phys. Chem. Solids 23 (1962) 249.

[7] E. Donges, Z. Anorg. Allg. Chemie 263 (1950) 112.

[8] L.M. Belyaev, V.A. Lyakhovitskaya, G.B. Netesov, M.V.

Mokhosoev, S.M. Aleikhina, Izv. Akad. Nauk SSSR,

Neorg. Mater. 1 (1965) 2178.

[9] V.I. Popolitov, B.N. Litvin, Kristallografiya 13 (1968) 571.

[10] H. Rau, A. Rabenau, Solid State Commun. 5 (1967) 331.

[11] K. Nassau, J.W. Shiever, M. Kowalchik, J. Crystal

Growth 7 (1970) 237.

[12] L. Haar, J.S. Gallagher, G.S. Kell, NBS/NRC Steam

Tables, Hemisphere Publishing Corp, New York, 1984.

[13] G.S. Manku, Inorganic Chemistry, Tata McGraw-Hill

Publishing Company limited, New Delhi, 1984, p. 340.Fig. 4. The DR spectrum of the rods.

Q. Yang et al. / Journal of Crystal Growth 233 (2001) 774–778 777

[14] T.F. Godimovich, A.A. Opalovskii, G.P. Sokhranenko,

Zh. Prikl. Khim. 60 (1987) 2188.

[15] D.R. Lide (Ed.), CRC Handbook of Chemistry and

Physics, various Editions, CRC Press Inc., Boca Raton,

FL.

[16] J. Yang, J.H. Zeng, S.H. Yu, L. Yang, Y.H. Zhang, Y.T.

Qian, Chem. Mater. 12 (2000) 2924.

[17] A. Ibanez, J.C. Jumas, J.O. Fourcade, E. Philippot, M.

Maurin, J. Solid State Chem. 48 (1983) 72.

Q. Yang et al. / Journal of Crystal Growth 233 (2001) 774–778778