The high temperature behaviour of A I B III X 2 VI chalcopyrites (A=Cu; B=Al, Ga und In; X=S, Se, Te) was studied by in-situ high temperature synchrotron radiation X-ray diffraction. Structural phase transitions from the α phase with chalcopyrite structure to the β phase with sphalerite structure were obtained in the compounds CuInX 2 and CuGaTe 2 . The driving force of this order-disorder transition is a Cu-In anti site occupancy starting in the critcal temperature region, nearly 10 K before the transition temperature. The order parameter of the phase transition, expressed ase e e n n n = − , goes within the critical region to zero according to IT -T trans I β with the critical exponent β = 0.35(7). Structural transitions were also obtained in CuAlTe 2 and CuGaSe 2 , but they show a different character. In the first compound it goes with the occurrence of a small two phases region, in the second with the formation of an other, unknown phase. Furthermore neither critical behaviour nor an anti site occupancy of the cations is observed.

The microhardness of eleven AIBIIICVI2 semiconducting compounds and thatof their CuGaS2xSe2(1−x), CuInS2xSe2(1−x), CuGaxIn1−xS2, CuGaxIn1−xSe2, and AgGaxIn1−xS2 solid solutions is experimentally studied in the plane (112). The functional dependences of the microhardness on the molar mass and the melting temperature are determined for the starting compounds in terms of which the microhardness values for all the AIBIIICVI2 compounds are estimated. The Debye temperatures of the AIBIIICVI2 compounds are calculated using the Madelung‐Einstein and Linde‐mann relations taking into account the microhardness and melting temperatures, respectively. It is established that the increasing metallicity of the compounds results in the decrease of their mechanical strength and thermal stability. The functional dependence of microhardness on composition is found for the solid solutions. It is established that the microhardness maximum is observed for the composition determined by the ratio of the molar masses of the starting compounds with \documentclass{article}\pagestyle{empty}\begin{document}$ x_{\max} = 1 - 2\frac{{\mu _1 - \mu _2}}{{\mu _1 + \mu _2}}. $\end{document}. The values of xmax and the maximum value of micrhardness for a number of solid solutions with one component substitution (anionic and cationic) are calculated on the basis of the AIBIIICVI2 ternary compounds.

The A' B' I' C;' semiconducting compounds attract great attention due to their potential application in photovoltaic /1/ and infrared non-linear optical devices /2/. In this connection it is interesting to study the properties of their solid solutions. The purpose of this note is to study the composition dependence of the band gap of CuInS2xSe2(1 been reported in /3 to 6/. solid solutions, some properties of which haveThe transmission spectra in the range from 6000 to 14000 cm-' were taken using a SP-700 C spectrophotometer as well as a special apparatus for spectra recording with wavelength modulation. All investigations were carried out on single crystal samples obtained by the chemical transport /6/ and two-temperature synthesis /7/. For measurements the specimens were polished and lapped from one side to a thickness of about 100 pm. The absorption coefficient a was calculated using the estimated transmission T and the reflectivity R given in /8/ by the well-known expression a = - R2]1'2]) where d is the sample thickness. The ternary chalcopyrite compounds Abrn%" being direct-gap semiconductors, the band gap E was determined by extrapolation of the linear part of (a -. ad) versus photon energy to the intersection with the photon energy axis. In wavelength-modulated experiments the band gap was determined by the position of the maximum in the dI/dh. spectrum. The measurements made with polarized light showed E to be independent of polarization or, in other words, the absorption processes near the absorption edge are independent of the polarization of irradiation, what is related by us to the absence of tetragonal distortion of the unit cell in the investigated system (for CuInS2 c/a = 2.015 and for CuInSe2 c/a * 2.003). 2 g g 1) Podlesnaya 1.7, 220726 Minsk, USSR.

Despite the fact that the ternary compounds AIBmCr and their solid solutions attract great attention due to their possible application in semiconducting devices, up to now there is scarce information about the properties of CuGax19 -xSe2 solid solutions in the literature /1 to 3/. In /2/ the temperature and composition dependences of the band gap (E ) of these solid solutions grown by a modified Bridgman method are investigated in the composition range 0 5 x 0.5, the optical and electrical properties of this system a r e studied at room temperature on specimens of some compositions obtained by a chemical transport method /3/. The results Of /2/ and /3/ on the composition dependence of the band gap essentially differ: in /2/ E changes linearly with composition, and in /3/ this dependence is nonlinear. These investigations were carried out on single crystals grown by a chemical transport method. The specimens were flat mirror-like plates, with surface corresponding to (112). The homcgeneity was tested by an X-ray method.The solid solution composition was determined taking into account the validity of Vegard' s law /1 to 3/, the accuracy of cornposition determination being *l mol%.The transmission spectra in the range from 6000 to 15000 crn" were taken using a SP-700 C spectrophotometer with polarized light. Previously the specimens were polished and lapped from one side to a thickness bf about 100 to 1501.1 m. The absorption coefficient ( OL ) was calculated using the estimated transmission (T) and reflection (R) by the well-known expression which takes into account multiple reflection:1) Podlesnaya 17, 220726 Minsk, USSR.

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