Ultrasonics Sonochemistry 17 (2010) 892–901

Contents lists available at ScienceDirect

Ultrasonics Sonochemistry

journal homepage: www.elsevier .com/locate /u l tsonch

Using of sonochemically prepared components for vapor phase growing of SbI3�3S8

M. Nowak a,*, M. Kotyczka-Moranska a, P. Szperlich a, Ł. Bober a, M. Jesionek a, M. Kepinska a, D. Stró _z b,J. Kusz c, J. Szala d, G. Moskal d, T. Rzychon d, J. Młynczak e, K. Kopczynski e

a Solid State Physics Section, Institute of Physics, Silesian University of Technology, Krasinskiego 8, 40-019 Katowice, Polandb Institute of Material Science, University of Silesia, Bankowa 12, 40-007 Katowice, Polandc Institute of Physics, University of Silesia, Bankowa 14, 40-007 Katowice, Polandd Department of Materials Science, Silesian University of Technology, Krasinskiego 8, 40-019 Katowice, Polande Institute of Optoelectronics, Military University of Technology, Gen. Sylwestra Kaliskiego 2, 00-908 Warsaw, Poland

a r t i c l e i n f o a b s t r a c t

Article history:Received 3 December 2009Received in revised form 19 January 2010Accepted 19 January 2010Available online 28 January 2010

Keyword:SonochemistryAdditive compoundsAntimony triiodide–sulfur

1350-4177/$ - see front matter � 2010 Elsevier B.V. Adoi:10.1016/j.ultsonch.2010.01.008

* Corresponding author. Tel.: +48 32 603 41 67; faxE-mail address: Marian.Nowak@polsl.pl (M. Nowa

The using of sonochemically prepared components for growth of SbI3�3S8 single crystals from the vaporphase is presented for the first time. The good optical quality of the obtained crystals is importantbecause this material is valuable for optoelectronics due to its non-linear optical properties. The productswere characterized by using techniques such as X-ray crystallography, powder X-ray diffraction, scanningelectron microscopy, energy dispersive X-ray analysis, high-resolution transmission electron microscopy,selected area electron diffraction, optical diffuse reflection spectroscopy and optical transmittance spec-troscopy. The direct and indirect forbidden energy gaps of SbI3�3S8 illuminated with plane polarized lightwith electric field parallel and perpendicular to the c-axis of the crystal have been determined. The sec-ond harmonic generation of light in the grown crystals was observed.

� 2010 Elsevier B.V. All rights reserved.

1. Introduction

Over the last years the non-linear optical (NLO) materials havebeen receiving a lot of attention because of their enormous poten-tial for many useful technological applications, e.g. second har-monic generation (SHG) and parametric generation of light. Highvalues of the second-order non-linear susceptibility and wide opti-cal transparency range are both required for such applications.Having these features, the optically non-linear molecular com-pounds which crystallize in non-centrosymmetric space groupsare of special interest [1–3]. Among them is the family of polarcrystals of tetrahedral triiodide adducts of trigonal symmetry, e.g.the SbI3�3S8. This material is known as: antimony triiodide–sulfur[4], antimony triiodide–sulfur crystalline complex [1], the 1:3 com-plex between antimony triiodide and sulfur [1,2], adduct (com-plex) of antimony triiodide with sulfur SbI3�3S8 [3,5], additioncompound SbI3�3S8 [6–8] or antimony iodide sulfide [9]. The crys-talline SbI3�3S8 exhibits second-order non-linear properties thatare quite strong in magnitude [1]. It is optically anisotropic anduniaxial negative [3]. The c-axis of this crystal is parallel to its opti-cal axis [1]. The ordinary refractive index (no = n11 = n22) is biggerin the ab plane (the plane of iodine atoms) than the extraordinaryindex (ne = n33) along the crystal trigonal c-axis [3].

ll rights reserved.

: +48 32 603 43 70.k).

The formation of solid addition compounds between antimonyiodide and sulfur was reported as early as 1908 [4]. Up to now theSbI3�3S8 crystals were grown by slow evaporation of the solventfrom a carbon disulphide solution containing antimony triiodideand sulfur [1,4,7,8,10,11]. Benzene and carbon tetrachloride wereused as solvents [1], too. Unfortunately NLO measurements needgood-quality crystals that are not obtained with these procedures[1].

The aim of this paper is to present a new procedure of growingSbI3�3S8 single crystals from sonochemically prepared intermedi-ate product. This approach is based on the following. Obviously,the good-quality single crystals of many materials are obtainedfrom vapor phase, e.g. by sublimation. Therefore, we decided touse this method to grow the single crystals of SbI3�3S8. To avoidthe easy decomposition of additive compound, we had to performthe sublimation in relatively low temperature. At sufficiently smalldimensions, the sublimation rate increases as predicted from clas-sical sublimation theory. Because the decreased temperature ofsublimation is one of the features of nanomaterials [12,13], oneshould use SbI3�3S8 nanoparticles as the source for sublimation.Up to now there is no information on such nanomaterial in litera-ture, but recently [14] the sonochemical method was used for di-rect preparation of nanocrystalline antimony sulfoiodide (SbSI).Therefore, we applied a similar sonochemical procedure to obtainthe SbI3�3S8. One should notice that the sublimation temperatureof small-molecule semiconductors can be reduced by sonocrystal-lization [15]. This is possible through the increase of crystal lattice

M. Nowak et al. / Ultrasonics Sonochemistry 17 (2010) 892–901 893

energy by the introduction of crystal defects, poor crystallinity, orthe formation of metastable polymorphs [15].

Fig. 2. Vapor pressures of the dried product of Sb, I and S (with atomic ratio 1:3:24)sonication in ethanol (A, B) and of the powdered single crystals of SbI3�3S8 (C, D) (A,C – first heating, B, D – second heating).

2. Experiment

The intermediate product, for the growth of SbI3�3S8 single crys-tals by sublimation, was prepared sonochemically from the con-stituents (the elements: antimony, sulfur and iodine), weighed inthe stoichiometric ratio for SbI3�3S8. Ethanol served as the solventfor this reaction. All the reagents used in our experiments were ofanalytical purity and were used without further purification. Anti-mony (99.95%) was purchased from Sigma–Aldrich. Sublimatedsulfur (pure p.a.), iodine (pure p.a.), and absolute ethanol (purep.a.) were purchased from POCH S.A. (Gliwice, Poland). In a typicalprocedure, the elemental mixture with stoichiometric ratio of e.g.0.421 g Sb, 2.662 g S and 1.317 g I, was immersed in 40 ml absoluteethanol at room temperature and under ambient pressure, whichwas contained in a glass cylinder of 40 mm internal diameter.The vessel was closed during the experiment to prevent volatiliza-tion of the precipitant in long time tests. It was partly submergedin water in an ultrasonic reactor (InterSonic IS-UZP-2, frequency35 kHz, with 80 W peak electrical power and 2 W/cm2 power den-sity guaranteed by the manufacturer). The sonolysis was carriedout at 323 K. Using the CP-401 pH-meter (Elmetron) with ERPt-13 and ERH-11S electrodes (Hydromet), we have measured theEh = 0.25 V and pH = 1.2 of the Sb–S–I–ethanol sol after 10 min ofsonication. Although the used experimental set up and the appliedprocedure were the same as the applied for sonochemical prepara-tion of SbSI ethanogel [14], in contrary to the former case, evenafter 10 h of sonication of the mixture of reagents (Sb:I:S withatomic ratio 1:3:24) a yellow sol was obtained. It was observedthat after a few hours some precipitates settled down. The solswere four times centrifuged to extract the products using theMPW-223e centrifuge, MPW Med. Instruments (Poland). Each timethe liquid above the sediment was replaced with pure ethanol towash the precipitates. At the end the yellow centrifuged productwas covered by colorless ethanol. As in the cases of sonochemicalpreparation of other nanocrystalline products, e.g. SbSI [14], theproducts were dried at room temperature (Fig. 1a).

To check the differences between sublimations of the driedproduct and powdered single crystals of SbI3�3S8, these two mate-rials have been entered into thermisil ampoules connected withOERLIKON PT50 turbomolecular drag pumping station (LeyboldVacuum). The pressure in the heated ampoules was measuredusing ACC1009 gauge (Alcatel). The temperature of the investi-gated material was measured during heating of the ampoules inoil bath using 211 Temperature Monitor (Lake Shore) with Pt-103 sensor. The heating rate was about 1.7 K/min. Fig. 2 presentstemperature dependences of pressures during two cycles of heat-ing of the investigated materials. One can see that in contrary to

Fig. 1. Images of dried product (a) of the sonication of Sb, I and S (with atomic ratio 1:sonochemical product.

the case of powdered SbI3�3S8 single crystals the pressure in anampoule with the product of Sb, I and S sonication increased withheating from 315 to 376 K, attained maximum of a broad peak(from 376 to 382 K), and then decreased in the temperature rangefrom 382 to 403 K. In the second cycle the temperature depen-dence of the pressure in the same ampoule did not show any spe-cial effect.

To obtain SbI3�3S8 single crystals from the vapor phase, thegrowing was performed in closed ampoules in vertical furnace,which was composed of two zones that temperatures could becontrolled independently. The sonochemically prepared materialwas put into thermisil ampoules of length 13.5 cm and diameter2.8 cm. Any seed crystal was not prepared. After evacuation (p =0.1 Pa) the ampoules were sealed. The lower part of the ampoulewas wrapped with a sheet of aluminum foil in order to obtain ahomogeneous temperature distribution in the source zone. If thereis a place where the temperature is not uniform in the source zone,nucleation tends to occur from undesired positions such as on theside wall of the ampoule or even on the top of the source materials.The aluminum foil restricts the position of nucleation only at thetop of the ampoule and allows the growth of large crystals. Thesource temperature was established T1 = 383(1) K and the seedtemperature was T2 = 353(1) K. The typical time of growing theSbI3�3S8 single crystal was 168 h. The typical size of the crystalgrown by this method was about 0.5 � 1 � 20 mm3. It had good-looking surfaces and no hollow was observed in it (Fig. 1b).

Characterization of the investigated materials was accom-plished using different techniques, such as powder X-ray diffrac-tion (XRD), X-ray crystallography, scanning electron microscopy(SEM), energy dispersive X-ray analysis (EDAX), high-resolution

3:24) in ethanol and (b) SbI3�3S8 single crystal grown from the vapor phase of the

Fig. 3. The powder XRD pattern of dried product of Sb, I and S (with atomic ratio1:3:24) sonication in ethanol ( , , , – peaks appropriate for SbI3�3S8 [7,20], S8

[21], SbI3 [22,23] and SbSI [24,25], respectively; details are presented in Table 1).

894 M. Nowak et al. / Ultrasonics Sonochemistry 17 (2010) 892–901

transmission electron microscopy (HRTEM), selected area electrondiffraction (SAED), optical diffuse reflection spectroscopy (DRS)and optical transmittance spectroscopy. The powder XRD measure-ments were performed on a JEOL JDX-7S X-ray diffractometer withgraphite-monochromatized CuKa radiation (k = 0.154056 nm). Theacceleration voltage was 40 kV with a 20 mA current flux. A scanrate of 0.05 s�1 was used to record the patterns in the 2h rangeof 10–80�. The crystal structure of the SbI3�3S8 single crystalswas characterized using an Oxford Diffraction KM4 kappa diffrac-tometer with Sapphire3 CCD detector and graphite-monochromat-ed Mo Ka radiation (0.71073 ÅA

0

). The crystal was mounted on aquartz glass capillary and cooled by a cold dry nitrogen gas stream(Oxford Cryosystems equipment). The temperature stability of theinstrument was ±0.2 K. Accurate cell parameters were determinedafter refinement using the program CrysAlis CCD [16]. For the inte-gration of the collected data the program CrysAlis RED was used[17]. The structure was first solved using the direct method withSHELXS-97 software, and then was refined with SHELXL-97 [18].

Scanning electron micrograph and EDAX patterns were takenon a Hitachi S-4200 scanning electron microscope with NoranInstruments EDS Voyager 3500 spectrometer. The size and struc-ture of the products of sonication of Sb, S and I were further char-acterized with HRTEM on a JEOL-JEM 3010 microscope, working at300 kV accelerating voltage. The point-to-point resolution was0.17 nm, and lattice resolution was 0.14 nm. The SAED investiga-tions were also conducted using a JEOL-JEM 3010 microscope.

The DRS measurements were carried out on a spectrophotome-ter PC2000 (Ocean Optics Inc.) equipped with an integrating sphereISP-REF (Ocean Optics Inc.). Spectra were recorded at room tem-perature, from 1000 to 350 nm. The standard WS-1 (Ocean OpticsInc.) was used as a reference. The diffuse reflectance values wereconverted to the Kubelka–Munk function proportional to theabsorption coefficient [19].

FK�MðRdÞ ¼ð1� RdÞ2

2Rd� a ð1Þ

where Rd describes the coefficient of diffuse reflectance and a is theabsorption coefficient of light in the investigated material.

For the optical transmittance measurements the SbI3�3S8 singlecrystals were mounted in 1.33 Pa vacuum in an optical D2209chamber (MMR Technologies, Inc.). This chamber was equippedwith R2205 Cryogenic Microminiature Refrigeration II-B Systemand K7701 temperature controller (MMR Technologies, Inc.).Investigations reported in this paper were performed at 293 K.The optical transmittance was measured using PC2000 (Ocean Op-tics Inc.) spectrophotometer with master and slave cards with 600lines grating (blazed at 500 and 400 nm, respectively). The spectro-photometer was equipped with appropriate waveguide cables andthe deuterium–halogen light source DH2000-FHS from Ocean Op-tics Inc. The multiple averaged spectral characteristics containing2048 data points for various wavelengths were registered usingthe OOI-Base program from Ocean Optics Inc. at constant temper-ature of the sample. The presented measurements were carried outfor normal illumination of the (0 �1 0) plane of the SbI3�3S8 singlecrystals. The incoming light beam was linear polarized with theelectric vector parallel (||) and perpendicular (?) to the c-axis ofthe crystal. The optical transmittance (To) data were transformedin the so called absorbance

A ¼ ad ¼ log1To

� �ð2Þ

where d is absorption path length.The SHG of k = 532 nm (2.33 eV) radiation was observed on

powered SbI3�3S8 crystals placed in slide glass container. The lasersystem consisted of a Nd:YAG/Cr:YAG microlaser (k = 1064 nm;

3 ns pulse duration, 14 lJ pulse energy) pumped with laser-diodeLIMO25-F100-LD808 was used in these tests. The non-linear signalwas detected by spectrometer Avantes AvaSpec-3648 after spectralseparation from the fundamental beam by spectral filtering. Thetime-dependence characteristics of the 1064 nm radiation laserpulse were measured with InGaAs ET-3000 photodiode by an Agi-lent Technologies MSO7104A oscilloscope. The data were collectedby PC. The detailed analysis of the SHG characteristics of the pre-sented material will be reported in near future.

3. Results and discussion

The powder XRD pattern of the product of sonication of Sb, I andS is shown in Fig. 3. The well-defined, sharp diffraction lines sug-gest the well-crystallized substance. Unfortunately, the identifica-tion of these lines (Table 1) shows that the investigated material isa mixture of many substances: SbI3�3S8, SbI3, SbSI, Sb3I and sulfur.

Fig. 4a presents the EDAX spectrum of the product of Sb, I and Ssonication in ethanol. Only characteristic peaks for antimony, io-dine and sulfur are observed (Fig. 4a). The ratios of the Sb, I andS components determined by EDAX investigations (Table 2) are dif-ferent from theoretical composition of SbI3�3S8. It is in agreementwith XRD data: the product of sonication is a mixture of differentcomponents. The SEM micrographs of this product also presentits complicated microstructure (Fig. 5a). Fig. 6 shows typical TEMimages of different nanoparticles found in this product. The HRTEMimages (Fig. 7) reveal that they exhibit good crystallinity and allowdetermining what kind of material they represent. One candistinguish three systems of clear lattice fringes (Fig. 7a) of thenanoplatelet from the dendritic pattern observed in Fig. 6a. Thefringe spacings of (1) 345.7(10) pm, (2) 402.5(9) pm, and (3)331.0(20) pm correspond to the interplanar distances 342.24,399.60, and 332.95 pm between the (2 0 0), (�1 1 2), and (0 3 1) or(0 2 2) planes of P21/c SbI3 crystal [22], respectively. Fig. 7b showsstructure of the nanowires observed in Fig. 6a. The observed fringespacings of 331.7(13) pm correspond to the interplanar distance324.94 pm between the (2 2 0) planes of SbSI crystal [24]. Fig. 7cpresents microstructure of a nanoparticle observed in Fig. 6c. Thefringe spacings equal (1) 315(3) pm, (2) 258(3) pm, and (3)313(4) pm. The first and latter ones may correspond to the inter-planar distances 317(17) pm observed in antimony subiodide(Sb3I) [26]. The second fringe spacing corresponds to the interpla-nar distance 268(16) pm also observed in Sb3I [26].

It should be underlined that the interplanar spacings corre-spond very well with the main X-ray diffraction lines presentedin Tables 3–5. Unfortunately, the nanowires observed in Fig. 6bwere too thick to obtain the HRTEM images. However, they gave

Table 1Comparison of interplanar spacings determined by powder XRD of the product of sonication of Sb, I and S (with atomic ratio 1:3:24) in ethanol with literature data for S8, SbI3�3S8,SbI3, SbSI and Sb3I; (Irel – relative intensities of the observed X-ray diffraction peaks).

Sonochemical product S8 Ref. [18] SbI33S8 Ref. [17] SbI3 Ref. [19] SbSI Ref. [21] Sb3I Ref. [23]

d (pm) Irel d (pm) hkl d (pm) hkl d (pm) hkl d (pm) hkl d (pm)

1242.1 820 1240.8 110578.0 390 577.07 113 579.70 110409.8 650 409.39 021385.6 1000 386.27 222357.7 560 358.20 600354.0 410 353.9344.6 800 345.66 026 344.15 520 342.24 200338.0 290 337.35 �122333.2 370 334.08 311 332.95 031022321.8 620 322.49 117

206320.97 130

312.0 790 311.63 �212309.2 930 311.78 313 308.42 051302.0 310 301.52 112 300.32 121 306.4299.4 340 299.31 241292.1 330 290.96 511284.7 370 285.83 044 285.03 211276.3 270 276.17 431268.0 370 268.31 242263.2 370 263.23 137 263.43 161 265.4252.4 230 252.30 701 252.49 221 252.50 040248.9 260 246.87 320242.2 260 243.08 317237.1 200 237.46 335229.3 210 229.48 021226.1 190 225.84 271214.9 210 214.53 123 �2 33211.4 270 212.09 062

319

M. Nowak et al. / Ultrasonics Sonochemistry 17 (2010) 892–901 895

good SAED patterns presented in Fig. 8. It should be noted that thenanowires observed in Fig. 6b are probably the SbI3�3S8 nanocrys-tals. They gave the appropriate electron diffraction pattern (Fig. 8)and the interplanar spacings determined using SAED (see Table 6)are comparable with those obtained from XRD and reported in lit-erature [20].

Figs. 9 and 10 present the SAED patterns and the simulated dia-grams for the SbI3 and Sb3I that are observed in Fig. 6a and c. Theinterplanar spacings determined using SAED diffraction patterns(see Tables 3 and 5) are only little different from values obtainedin XRD and HRTEM investigations as well as from the data reportedin literature [22,26].

To establish the uncertainties of the d-spacings determinedusing the XRD, the instrumental parameters were evaluated usingthe NIST Alumina plate. Peak positions were defined by Pearson VIIfunction. The uncertainties of the d-spacings determined usingHRTEM have been estimated as the standard deviation of the aver-age value calculated from series of results. The SAED d-spacingswere determined from the electron diffraction patterns using theDigitalMicrograph software of GATAN Company. In general, thestandard accuracy of the d-spacing determination from the X-rayspectra is much higher than the accuracy for the TEM methods,which is at most 1 pm. Additionally it should be noted that it is dif-ficult to maintain the same sample temperature in our XRD andHRTEM measurements. Taking the above into account it can beclaimed that the results obtained from different methods are ingood agreement.

Fig. 11 presents comparison of the diffuse reflectance spectra ofthe dried product (curve A) of sonication of antimony, iodide andsulfur (with atomic ratio 1:3:24) in ethanol with data publishedfor SbI3�3S8 single crystal [3], antimony subiodide [27], SbSI ethan-ogel [14], as well as sulfur and SbI3 in ethanol. To obtain more de-tailed information about the product of Sb, I and S sonication, thedeconvolution [28] of the spectrum of Kubelka–Munk function

was done (Fig. 12). The best results were obtained for FK–M =9.4(1)�FK–M(SbI3�3S8) + 6.56(3)�FK–M(Sb3I) + 0.713(4)�FK–M(SbI3) +0.117(2)�FK–M(SbSI) + 0.01(13)�FK–M(S). One can see that the prod-uct consists of SbI3, SbSI, Sb3I, SbI3�3S8 and sulfur. It is in agreementwith the results of XRD, HRTEM and SAED investigations. Thepresented results are qualitative. The quantitative ones may be ob-tained in future investigations on the influence of the concentrationof the components on Kubelka–Munk function.

In summary, the sonochemical formation of SbI3�3S8 nanowiresis accompanied with the formation of other species, e.g. SbI3 [29],Sb3I [26], SbSI [14], also iodine can be sonochemically oxidized totriiodide (I�3 ) by OH� radicals produced during cavitation [30,31].However, the oxidative power of the I�3 ion is lower than that of io-dine molecules, I2, itself [32]. So, the I�3 seems to be not essential forthe presented sonochemical preparation of SbI3�3S8. The investi-gated Sb–S–I–C2H5OH system is somewhat similar to the Sb–S–I–H2O system used in hydrothermal synthesis of bulk SbSI-type crys-tals. The useful yield of different single crystals produced by hydro-thermal synthesis depends on concentration and composition ofthe solvents, ratio of the initial components in the charge, Eh andpH of the medium, and temperature [33]. Eh–pH diagrams havebecome a standard method of illustrating equilibrium relation-ships between dissolved and solid species. Fig. 13 presents com-parison of the measured by us Eh and pH values after 10 min ofsonochemical preparation of SbI3�3S8, SbI3, Sb3I and SbSI in ethanolas well as the data obtained after 10 min sonication of powderedsingle crystals of SbI3 in ethanol. According to [34] the ðSbI3Þ� com-plexes are durable for pH < 3. Area between dashed lines a and b inFig. 13 represents the reported in [33] Eh and pH ranges in whichall Sb, S, and I elements should be in the appropriate valence statesfor Sb3+S2�I1� synthesis, i.e. for the hydrothermal synthesis of bulkSbSI in Sb–S–I–H2O system. One can notice that the registered byus values of Eh and pH in the case of sonochemically preparedcomponents for vapor phase growing of SbI3�3S8 are little different

Fig. 4. EDAX spectra of dried product (a) of the sonication of Sb, I and S (withatomic ratio 1:3:24) in ethanol and (b) SbI3�3S8 single crystal grown from the vaporphase of the sonochemical product.

Table 2Comparison of the experimentally determined chemical contents of dried product ofthe sonication of Sb, I and S (with atomic ratio 1:3:24) in ethanol and SbI3�3S8 singlecrystal grown from the vapor phase of the sonochemical product with the theoreticalcontent of SbI3�3S8.

Material Concentration of elements determined by EDAX(at.%)

Sb S I

Sonochemical product 7(1) 88(1) 5(1)Single crystal 4(1) 86(1) 10(1)Theoretical composition 3.6 85.7 10.7

896 M. Nowak et al. / Ultrasonics Sonochemistry 17 (2010) 892–901

from the measured in the case of sonochemical preparation of SbSIand Sb3I (Fig. 13). They are also little above the upper limit (line b)calculated in [33] as appropriate for the SbSI synthesis, i.e. theupper limit of stability of the sulfur ions S2�. Therefore, the coexis-tence of the SbSI, Sb3I and SbI3�3S8 species in the sonicated solutionis justified. The sonochemical mechanisms of preparation of theSbSI and Sb3I were postulated in [35,26], respectively. The probablereaction route of SbI3�3S8 synthesis and the mechanism of forma-tion of its nanowires using elemental Sb, S and I in the presence

Fig. 5. Typical SEM micrographs of (a) dried product of Sb, I and S (with atomic ratio 1:3:of the sonochemical product.

of ethanol under ultrasonic irradiation can be summarized asfollows:

(1) iodine, I2, dissolved in ethanol reacts with antimony andforms the antimony triiodide, SbI3, also dissolved in ethanol

24) soni

2Sbþ 3I2 ! 2SbI3 ð3Þ

(2) the solid structure of sulfur is definitely molecular and con-tains S8 molecules which are symmetrical puckered ringswith S–S distance 0.12 nm and bond angle a = 105� [36].Chemical evidence suggests that the molecule is S8 even inthe melt at temperatures not too far above the melting point[36]. When a cavitation bubble collapses violently near asolid surface, liquid jets are produced and high-speed jetsof liquid are driven into the surface of a solid. These jetsand shock waves cause removal of small particles from thesurface. So, the ultrasonic irradiation facilitates the cleavageof solid sulfur into S8 molecules.

(3) the ultrasonically produced small nanoparticles have ahigher reactivity toward the formation of new compounds.Hence the released S8 react with SbI3 to yield SbI3�3S8

molecules

SbI3 þ 3S8 ! SbI3 � 3S8 ð4Þ

in which charge transfer bonds are formed between the threeiodine atoms of a particular pyramidal SbI3 molecule (theelectron acceptor; the Lewis acid) and three sulfur atomsbelonging to its three partner S8 rings (the electron donors;the Lewis or Bronsted base) [7,37,38].

(4) the created SbI3�3S8 molecules, under the microjets andshockwaves formed at the collapse of the bubbles arepushed towards each other and are held by chemical forces.Therefore, the nuclei of SbI3�3S8 are formed as a result of theinterparticle collisions (see e.g. [39]).

cation in ethanol and (b) SbI3�3S8 single crystal grown from the vapor phase

Fig. 6. Typical TEM images of individual nanoparticles observed in the product of sonication of Sb, I and S (with atomic ratio 1:3:24) in ethanol (a – SbSI nanowires anddendritic patterns observed on the platelets of SbI3; b – nanowires of SbI3�3S8 and agglomerates of nanoparticles of Sb3I; and c – nanoparticles of Sb3I).

Fig. 7. Typical HRTEM images of individual nanoparticles observed in the product of sonication of Sb, I and S (with atomic ratio 1:3:24) in ethanol (a – SbI3 nanoplatelet fromthe dendritic pattern observed in Fig. 6a. The fringe spacings of (1) 345.7(10) pm, (2) 402.5(9) pm and (3) 331(2) pm correspond to the interplanar distances 342.24, 399.60and 332.95 pm between the (200), (�1 12), and (031) or (022) planes of P21/c SbI3 crystal [22], respectively; b – SbSI nanocrystal observed in Fig. 6a. The fringe spacing of331.7(13) pm corresponds to the interplanar distance 324.94 pm between the (220) planes of SbSI crystal [24]; and c – nanoparticle of Sb3I observed in Fig. 6c. The fringespacings equal (1) 315(3) pm, (2) 258(3) pm, and (3) 313(4) pm correspond to the interplanar distances observed in Sb3I [26]).

Table 3Comparison of interplanar spacings determined by powder XRD, SAED and HRTEM ofSbI3 observed in the product of sonication of Sb, I and S (with atomic ratio 1:3:24) inethanol.

Results ofthe XRD

Results ofthe SAED

Results ofthe HRTEM

LiteratureRef. [19]

dhkl (pm) Circle dhkl (pm) Sign dhkl (pm) hkl dhkl (pm)

2 402.5(9) �1 12 399.60344.6 1 345.7(10) 200 342.24338.0 �1 22 337.35333.2 3 331.0(20) 031

022332.95

321.8 130 320.97312.0 �212 311.63

3 306.1 �212 311.63302.0 112 301.52

1 268.6 122 271.50252.4 221 252.50214.9 �2 33 123 214.53

4 190.6 �3 04 190.285 176.3 302 178.602 150.3 115 150.26

Table 4Comparison of interplanar spacings determined by powder XRD, SAED and HRTEM ofSbSI observed in the product of sonication of Sb, I and S (with atomic ratio 1:3:24) inethanol.

Results of the XRD Results of the HRTEM Literature Ref. [21]

dhkl (pm) Mark dhkl (pm) Plane dhkl (pm)

1 331.7(13) 220 324.94302.0 121 300.32284.7 211 285.03252.4 040 252.50248.9 320 246.87

Table 5Comparison of interplanar spacings determined by powder XRD, SAED and HRTEM ofSb3I observed in the product of sonication of Sb, I and S (with atomic ratio 1:3:24) inethanol.

Results ofthe XRD

Results ofthe SAED

Results ofthe HRTEM

LiteratureRef. [23]

dhkl (pm) Circle dhkl (pm) Sign dhkl (pm) Method dhkl (pm)

5 537.86 381.8

354.0 XRD 353.9SAED 345

302.0 1 315.(3) XRD 306.4HRTEM 317(17)

3 313.(4)

1 289.3 SAED 2983 278.52 273.0

263.2 2 258.(3) XRD 265.4(42)HRTEM 268(16)

4 190.6 SAED 180

M. Nowak et al. / Ultrasonics Sonochemistry 17 (2010) 892–901 897

(5) the freshly formed nuclei in the solution are unstable andhave the tendency to grow into nanowires along the c-axisparallel to the unshared pair of electrons of the Sb atom inSbI3 molecule (see Fig. 14). Thus, this solid material has atendency to form highly anisotropic, 1D structures. Localturbulent flow associated with cavitation and acousticstreaming greatly accelerates mass transport in the liquidphase;

(6) the aggregated SbI3�3S8 nanowires produce larger species;during the sonication time, the surface state of the nano-wires might change: the dangling bonds, defects, or trapsdecrease gradually, and the species grow until the surface

Fig. 10. Electron diffraction pattern of an individual nanoparticle of Sb3I observedin Fig. 6c (the determined interplanar distances are presented in Table 5).

Fig. 8. Electron diffraction pattern of an individual SbI3�3S8 nanowire observed inFig. 6b and its simulated diagram (the determined interplanar distances arepresented in Table 6).

Table 6Comparison of interplanar spacings determined by powder XRD, SAED and HRTEM ofSbI3�3S8 observed in the product of sonication of Sb, I and S (with atomic ratio 1:3:24)in ethanol.

Results of the XRD Results of the SAED Literature Ref. [17]

dhkl (pm) Circle dhkl (pm) Plane dhkl (pm)

1242.1 110 1240.8409.8 021 409.39357.7 600 358.20344.6 520 344.15309.2 6 306.0 051 308.42299.4 2 299.0 241 299.31292.1 4 290.6 511 290.96276.3 431 276.17263.2 161 263.43252.4 701 252.30226.1 271 225.84

1 0.1892 854 0.189223 0.1579 912 0.157915 0.1587 13,1,0 0.15887

Fig. 9. Electron diffraction pattern of an individual SbI3 nanocrystal from thedendritic pattern observed in Fig. 6a and its simulated diagram (the determinedinterplanar distances are presented in Table 3).

Fig. 11. Diffuse reflectance spectra of the dried product (A) of Sb, I and S (withatomic ratio 1:3:24) sonication in ethanol, j – SbI3�3S8 single crystal [3], (B)antimony subiodide [27], (C) SbSI ethanogel [14], (D) sulfur in ethanol, (E) SbI3 inethanol, and (F) powdered crystals of SbI3�3S8 grown from the vapor phase of thesonochemical product. The last characteristic was normalized to 80% of themaximum reflectivity, as it was done in Ref. [3]).

Fig. 12. Spectrum of Kubelka–Munk function (j) calculated for the diffusereflectance of the dried product of Sb, I and S sonication presented by curve A inFig. 11. Dashed curve represents the fitted spectral dependence of the followingsum of Kubelka–Munk functions: 0.713(4)�FK–M(SbI3) + 0.117(2)�FK–M(SbSI) +6.56(3)�FK–M(Sb3I) + 9.4(1)�FK–M(SbI3�3S8) + 0.01(13)�FK–M(S) calculated for the dif-fuse reflectance data presented in Fig. 11. The solid curves show the appropriateKubelka–Munk functions of SbI3 (A), SbSI (B), antimony subiodide (C), SbI3�3S8 (D),and sulfur (E) in ethanol (description in the text).

898 M. Nowak et al. / Ultrasonics Sonochemistry 17 (2010) 892–901

state becomes stable; surface corrosion and fragmentationby ultrasound irradiation, results in the formation of regularnanowires.

Compounds of low volatility, which are unlikely to enter cavita-tion bubbles, experience a high-energy environment resulting fromthe pressure changes associated with the propagation of the acous-tic wave or with shock waves; or they can react with radical spe-cies generated by sonolysis of the solvent [30]. In the presented

Fig. 13. Eh–pH diagram of results obtained after 10 min of sonochemical prepa-ration of SbI3�3S8 ( ), SbI3 ( ), Sb3I ( ) and SbSI (d) in ethanol as well as the dataobtained after 10 min sonication of powdered single crystals of SbI3 ( ) in ethanol(description of the experiments in Table 7; area between dashed lines a and brepresents the ranges of pH and Eh values established in Ref. [33] as necessary forhydrothermal synthesis of bulk SbSI).

M. Nowak et al. / Ultrasonics Sonochemistry 17 (2010) 892–901 899

case, the reagents Sb and S are much less volatile than the ethanoland the iodine, so they stay in the interfacial region of the cavita-tion bubbles to yield SbI3�3S8 nanocrystals. The fine crystallinity ofthe products, which was confirmed by the SAED results (Fig. 8) ofan individual SbI3�3S8 nanowire observed in Fig. 6b, strongly sup-ports this hypothesis.

It should be underlined that the SbI3 molecules deform appre-ciably in the crystalline state [6] and antimony triiodide does notform molecular crystals. On the other hand, the SbI3�3S8 has a sin-gle molecular structure. The unit cell of SbI3�3S8 contains one mol-ecule of the adduct in which the antimony triiodide molecule isplaced on the trigonal axis of the crystal, with its molecular dipolemoment parallel to it, and the sulfur S8 rings are situated withinthe mirror planes and with their chief axes nearly parallel to thechief axis of the crystal [7]. A lengthening of the Sb–I distance from271.9 to 274.7 pm due to the formation of a bond between iodineand sulfur was observed [5]. At the same time the I–I distance isdecreased from 413.8 to 410.1 pm, corresponding to a decreasein the I–Sb–I angle from 99.1� to 96.6� [5]. There is therefore achange in the antimony triiodide molecule due to the formationof the addition complex. Each iodine atom is attached to a sulfuratom of a particular S8 molecule with an I–S distance of 360 pmand an angle Sb–I–S of 169.4� [7]. The sulfur ring is in SbI3�3S8,within the probable limits of error, identical with that found in

Fig. 14. Unit cell packing diagrams for SbI3�3S8 adduct crystal at 290.0(2) K down crystallbetween iodine I and sulfur S atoms in the adduct molecules. The cell constants are a =

the orthorhombic modification of sulfur (the mean S–S bond dis-tance is 204.6 pm (in sulfur 204.8 pm) and the S–S–S angle is107�510 (in sulfur 107�550) [7]).

Additional short intermolecular distances also occur: each anti-mony atom has three iodine neighbors at distances of 385 pm, allbelonging to the nearest antimony triiodide molecule situated onthe same trigonal axis [7]. These Sb–I distances are certainly short-er than the van der Waals radius sum and indicate a comparativelystrong interaction between the atoms [7]. It would actually appearpossible that the antimony atom in the triiodide molecule mayhave acceptor properties sufficiently strong to result in the forma-tion of addition compounds depending on charge transfer bondsbetween antimony atoms and donor atoms belonging to partnermolecules [7]. Further, each iodine atom has in addition to the sul-fur atom mentioned above (at a distance of 360 pm) four sulfurneighbors all belonging to different sulfur rings with I–S separa-tions of 378 pm resp. 388 pm. Here, contrary to the finding in theformer case, the angles Sb–I–S (72.2� and 122.9�) are far fromapproaching 180� [7]. So, it appears very probable that the greatstability of the crystalline SbI3�3S8 compound depends not onlyon the shortest I–S charge transfer bond but also to some extenton the just mentioned interactions between antimony and iodineand between iodine and sulfur atoms [7]. In this connection thefact should not be forgotten that there is rather strong evidenceof 1:3 complexes (e.g. between iodoform and quinoline) beingpresent even in dilute solution of the analogous addition com-pound (see Ref. in [7]). It should be underlined that antimony, sul-fur and iodine can form onium ions [40]. These ions are formedwhen an unshared pair of electrons on the central atom with zeroformal charge is used to form an additional covalent bond [40].Onium ions are considered to be the positively charged higher-valency (higher-coordination) compounds [40].

The higher pressure of gases above the nanocrystalline productof Sb, I and S sonication than above the single crystals of SbI3�3S8

(Fig. 2) is in agreement with the results reported in [12,13,15].One should notice that evaporation/sublimation of the sonochem-ically prepared SbI3�3S8 is most efficient in temperatures from 376to 382 K while the melting point of bulk SbI3�3S8 crystals is 389–391 K [7]. Bulk SbSI melts without decomposing at temperatureof about 673 K [41]. The temperatures of melting of bulk SbI3

and sulfur are 443.6 K [42] and 392 K [36], respectively. The subli-mation pressure of SbI3 at temperatures lower than 403 K is verylow [43]. The Sb3I melts above 423 K.

The results of EDAX of the vapor grown SbI3�3S8 single crystals(Fig. 4b) are well comparable with the theoretical composition ofSbI3�3S8 (Table 2). In contrast with the sonochemical product thegrown crystal was homogeneous and had mirror like surfaces (Figs.1 and 5). The X-ray analysis of the grown crystal confirmed its

ographic c-axis (a) and down a-axis (b). The dotted lines indicate the closest contactsb = 2483.57(11) pm, c = 442.44(2) pm.

Fig. 15. Fitting of the absorbance spectra of SbI3�3S8 single crystal illuminated withplane polarized light with electric field parallel (h) and perpendicular (j) to thec-axis of the crystal (T = 293 K). Solid curves represents the least square fittedtheoretical dependences for the sum of constant absorption term as well as directand indirect forbidden absorptions (description in the text; values of the fittedparameters are given in Table 8).

Table 8Comparison of direct (EgDf) and indirect (EgIf) energy gaps and other absorptionparameters obtained from the fittings of the absorbance spectra of SbI3�3S8 singlecrystal illuminated with plane polarized light with electric field parallel (||) andperpendicular (?) to the c-axis of the crystal (T = 293 K).

Parameters Values of the fitted parameters

|| ?

EgDf (eV) 2.71 2.63EgIf (eV) 2.45 2.35A3 (1/[(eV)1/2 m]) 211.1 185.4A60 (1/[(eV)3 m]) 85.54 63.12A0 (1/m) 3.035 2.807

900 M. Nowak et al. / Ultrasonics Sonochemistry 17 (2010) 892–901

trigonal rhombohedral structure with the space group R3 m. Theunit cell contains three molecules of the adduct (Z = 3) in whichthe antimony triiodide molecule is placed on the trigonal axis c3

of the crystal, with its molecular dipole moment parallel to it,and the sulfur S8 molecules have three mirror planes. The molecu-lar structure of SbI3�3S8 with the numbering scheme and displace-ment ellipsoids at 290.0(2) K is presented in Fig. 14. Fig. 14a showsthe unit cell packing diagram viewed normal to the (0 0 1) plane,i.e., down the crystal 3-fold c-axis of SbI3�3S8. Fig. 14b shows the(0 1 0) plane of the unit cell, where the molecules can be seen inthe direction normal to the crystal c-axis. The dotted lines indicatethe directions of the possible intermolecular charge transfer inter-actions between iodine and sulfur atoms in the adduct molecules.The cell constants are a = b = 2483.57(11) pm, c = 442.44(2) pm.Values of these parameters are comparable with the data pub-lished in Ref. [7]. The more detail multitemperature X-ray analysisof the SbI3�3S8 crystals will be presented in near future.

Fig. 15 presents the spectral characteristics of absorbance calcu-lated from optical transmittance of SbI3�3S8 single crystal. Applyingthe method of simultaneous fitting of many mechanisms ofabsorption to the spectral dependence of absorbance (see Ref.[19]), these data were used to determine the optical energy gapof the SbI3�3S8 single crystal. In this method the following leastsquare function has been minimized:

v2 ¼Xn

i¼1

hðFK—MðhmiÞ � B

Xj

ajðhmiÞi2

ð5Þ

where i represents photons of different energy, aj describes variousmechanisms of light absorption, and B is the proportionality factor.

Fig. 15 presents the spectrum of FK–M of the investigatedSbI3�3S8 single crystal and the best fitted theoretical dependence

Table 7Masses of reagents used in Eh–pH investigations of sonochemically prepared variousnanomaterials and the powdered SbI3 crystals.

Weight ofreagents

Sonochemically prepared nanomaterials PowderedSbI3 crystals

SbI3�3S8 SbI3 Sb3I SbSI

Sb (g) 0.1052 0.1053 0.249 0.9472 –S (g) 0.6655 – – 0.25 –I (g) 0.3292 0.3296 0.796 0.987 –Total weight (g) 1.0999 0.4349 1.045 2.1842 0.4344C2H5OH (ml) 10 10 10 10 10

appropriate for the sum of indirect forbidden absorption withoutexcitons and phonon statistics (a1), direct forbidden absorptionwithout excitons (a2), and constant absorption term (a3) (see Ref.cited in Refs. [19,44]):

a1 ¼ A60ðhm� E3gIf Þ for hm > EgIf ð6aÞ

a2 ¼A3

hmðhm� EgDfÞ3=2 for hm > EgDf ð6bÞ

a3 ¼ A0 ð6cÞ

where EgIf represents the indirect forbidden energy gap, EgDf is thedirect forbidden energy gap, A60, A3 are constant parameters. Theconstant absorption term A0 is an attenuation coefficient that isconsidered as the sum of the scattering and absorption independentof photon energy (hm) near the absorption edge. The fitting pre-sented in Fig. 15 is rather good. Values of the fitted parametersare given in Table 8. One can notice in Fig. 15 that, as it was reportedin [3], the SbI3�3S8 adduct absorbs light very little at wavelength532 nm (the wavelength of radiation effectively generated by SHGusing the Nd:YAG/Cr:YAG microlaser).

4. Conclusions

The product of sonication of Sb, I and S (with atomic ratio1:3:24) in ethanol is a mixture of SbI3, Sb3I, SbSI, SbI3�3S8 and sul-fur nanoparticles. The SbI3�3S8 nanowires are effectively grown viaa solid-solution–solid pathway under the ultrasonic irradiation.They can be successfully used as raw material for growth ofSbI3�3S8 single crystals from the vapor phase. The temperature ofthe source zone can be equal T1 = 383 K while the seed tempera-ture can be T2 = 353 K. The grown single crystals of SbI3�3S8 havegood optical properties. They are suitable for generation of secondharmonic of light.

For the first time the optical energy gap of the SbI3�3S8 has beendetermined. At 293 K this material has direct and indirect energygaps EgDf = 2.71 eV and EgIf = 2.45 eV for plane polarized radiationwith the electric vector parallel to the c-axis of the crystal. At thesame temperature the optical energy gaps for plane polarized radi-ation with the electric vector perpendicular to the c-axis of thecrystal are equal EgDf = 2.63 eV and EgIf = 2.35 eV.

Acknowledgement

This paper was partially supported by the MNiSzW (Poland) un-der Contract No. NN507157733.

References

[1] A. Samoc, M. Samoc, P.N. Prasa, A. Krajewska-Cizio, Second-harmonicgeneration in the crystalline complex antimony triiodide–sulfur, J. Opt. Soc.Am. B 9 (1992) 1819–1824.

[2] J.F. Kelly, E.R. Krausz, A. Samoc, M. Samoc, A.C. Willis, Crystal structure of thesecond-order nonlinear optical addition complex, Aust. J. Chem. 55 (2002)709–714.

M. Nowak et al. / Ultrasonics Sonochemistry 17 (2010) 892–901 901

[3] A. Samoc, M. Samoc, B. Luther-Davies, J.F. Kelly, E.R. Krausz, A.C. Willis, Newsecond-order nonlinear octupolar materials, Mol. Cryst. Liq. Cryst. 415 (2004)179–195.

[4] M.V. Auger, Sur un nouveau type de combinaison du soufre avec certainsiodures, C.R. Acad. Sci. 146 (1908) 477–479.

[5] A. Almenningen, T. Bjorvatten, An electron diffraction investigation of themolecular structure of antimony triiodide, Acta Chem. Scand. 17 (1963) 2573–2574.

[6] S. Ogawa, Nuclear quadrupole resonances in arsenic and antimony trihalidesand sulphur molecular addition compounds, J. Phys. Soc. Jpn. 13 (1958) 618–628.

[7] T. Bjorvatten, O. Hassel, A. Lindheim, Crystal structure of the additioncompound SbI3:3S8, Acta Chem. Scand. 17 (1963) 689–702.

[8] W.S. Fernando, Single crystal Raman spectra of SbI3–3S8, CHI3–3S8 and AsI3–3S8, J. Inorg. Nucl. Chem. 43 (1981) 1141–1145.

[9] Antimony Iodide Sulfide, JCPDS-International Centre for Diffraction Data 2000,PCPDFWIN v. 2.1, Card File No. 71-2024.

[10] H. Robinson, H.G. Dehmelt, W. Gordy, Nuclear quadrupole couplings in solidbromides and iodides, J. Chem. Phys. 22 (1954) 511–515.

[11] M. Demassieux, Étude cristallographique de certain iodosulfures, Bull. Soc.Franc. Miner. 32 (1909) 387–396.

[12] X. Zhang, Y. Ding, Y. Zhang, Y. Hao, G. Meng, L. Zhang, Thermal behavior ofantimony nanowire arrays embedded in anodic aluminum, J. Thermal Anal.Calorim. 89 (2007) 493–497.

[13] J.W.L. Yim, B. Xiang, J. Wu, Sublimation of GeTe nanowires and evidence of itssize effect studied by in situ TEM, J. Am. Chem. Soc. 131 (2009) 14526–14530.

[14] M. Nowak, P. Szperlich, Ł. Bober, J. Szala, G. Moskal, D. Stró _z, Sonochemicalpreparation of SbSI gel, Ultrason. Sonochem. 15 (2008) 709–716.

[15] T. Lee, S.C. Chang, Sublimation point depression of small-moleculesemiconductors by sonocrystallization, Cryst. Growth Des. 9 (2009) 2674–2684.

[16] Oxford Diffraction, CrysAlis RED, Version 1.171.29, Oxford Diffraction Ltd.,2006.

[17] Oxford Diffraction, CrysAlis CCD, Version 1.171.29, Oxford Diffraction Ltd.,2006.

[18] G.M. Sheldrick, A short history of SHELX, Acta Cryst. A64 (2008) 112–122.[19] M. Nowak, B. Kauch, P. Szperlich, Determination of energy band gap of

nanocrystalline SbSI using diffuse reflectance spectroscopy, Rev. Sci. Instrum.80 (2009) 046107-1–046107-3.

[20] Antimony Iodide Sulfide, JCPDS-International Centre for Diffraction Data,PCPDFWIN v. 2.1, Card File 71-2024, 2000.

[21] Sulfur, JCPDS-International Centre for Diffraction Data, PCPDFWIN v. 2.1, CardFile 85-0799, 2000.

[22] Antimony Iodide, JCPDS-International Centre for Diffraction Data, PCPDFWINv. 2.1, Card File 75-1417, 2000.

[23] S. Pohl, W. Saak, Zur Polymorphie von Antimontriiodid. Die Kristallstrukturvon monoklinem SbI3, Z. Kristallogr. 169 (1984) 177–184.

[24] Antimony Sulfide Iodide, JCPDS-International Centre for Diffraction Data,PCPDFWIN v. 2.1, Card File 74-0149, 2000.

[25] E. Dönges, Über Chalkogenohalogenide des dreiwertigen Antimons undWismuts. I. Über Thiohalogenide des dreiwertigen Antimons und Wismuts,Z. Anorg. Allg. Chem. 263 (1950) 112–132.

[26] M. Nowak, P. Szperlich, E. Talik, J. Szala, T. Rzychon, D. Stró _z, A. Nowrot, B.Solecka, Sonochemical preparation of antimony subiodide, Ultrason.Sonochem. 17 (2010) 219–227.

[27] M. Nowak, P. Szperlich, M. Kepinska, Optical properties of sonochemicallyprepared antimony subiodide, Thin Solid Films.

[28] R.W. Frei, D.E. Ryan, V.T. Lieu, Simultaneous analysis of two-componentsystems by diffuse reflectance spectroscopy, Can. J. Chem. 44 (1966) 1945–1950.

[29] R.F. Rolsten, Iodide Metals and Metal Iodides, Wiley, New York, 1961.[30] G. Cravotto, P. Cintas, Power ultrasound in organic synthesis: moving

cavitational chemistry from academia to innovative and large-scaleapplications, Chem. Soc. Rev. 35 (2006) 180–196.

[31] M.H. Entezari, P. Kruus, Effect of frequency on sonochemical reactions II.Temperature and intensity effects, Ultrason. Sonochem. 3 (1996) 19–24.

[32] M. Lindsjo, Ph.D. Thesis, KTH Chemical Science and Engineering, Stockholm,2005.

[33] V.I. Popolitov, B.N. Litvin, in: A.N. Lobachev (Ed.), Crystallization Process underHydrothermal Conditions, Consultants Bureau, New York, 1973, pp. 57–72.

[34] B.N. Litvin, V.I. Popolitov, Hydrothermal method of preparation of theAVBVICVII compounds, Izv. AN SSSR, Neorg. Mater. 6 (1970) 575–576.

[35] M. Nowak, B. Kauch, P. Szperlich, D. Stró _z, J. Szala, T. Rzychon, Ł. Bober, B.Toron, A. Nowrot, Sonochemical preparation of SbS1–xSexI nanowires,Ultrason. Sonochem. 17 (2010) 487–493.

[36] B.E. Warren, J.T. Burwell, The structure of rhombic sulphur, J. Chem. Phys. 3(1935) 6–8.

[37] O. Hassel, The structure of addition compounds, especially those in whichhalogens act as electron-acceptors, Proc. Chem. Soc. (1957) 250–255.

[38] O. Hassel, Nobel Lecture, <http://nobelprize.org/nobel_prizes/chemistry/laureates/1969/hassel-lecture.pdf>.

[39] A. Gedanken, Using sonochemistry for the fabrication of nanomaterials,Ultrason. Sonochem. 11 (2004) 47–55.

[40] G.A. Olah, K.K. Laali, Qi Wang, G.K. Surya Prakash, Onium Ions, Wiley and Sons,New York, 1998.

[41] E.I. Gerzanich, V.A. Lyakhovitskaya, V.M. Fridkin, B.A. Popovkin, SbSI and otherferroelectric AVBVICVII materials, in: E. Kaldis (Ed.), Current Topics inMaterials Science, vol. 10, North-Holland, Amsterdam, 1982, pp. 55–190.

[42] J. Trotter, N.Z. Zobel, The crystal structure of SbI3 and BiI3, Z. Kristallogr. 123(1966) 67–72.

[43] D. Ferro, B. Nappi, V. Piacente, Vapour pressure of antimony triiodide, J. Chem.Thermodyn. 11 (1979) 193–201.

[44] J.I. Pankove, Optical Properties of Semiconductors, Prentice-Hall, Inc.,Englewood Cliffs, NJ, 1971.