In recent years a number of papers has been devoted to studies concerning solid solution systems, mainly the substitutions of components on the basis of tin and germanium tellurides within the region close to them in composition. Such interest in these systepls has been aroused both by the physical properties of the above tellurides, in particular those of tin telluride (1 to 4) and by the possibility of using the compositions of solid solutions based on them, in various thermoelectric converters.The main purpose of this investigation is to study the effect of partial substitution of tin by the second-group elements on the thermoelectric properties of the SnTe--A Te-type solid solutions (where A = Zn, Cd, Hg) to make clear both the retention of the complex zonal structure and the defective behaviour of the crystal lattice peculiar to SnTe. I1There is only one piblication (5) dealing with studies on the solubility of CdTe in SnTe. We have studied the phase diagrams of SnTe-Zn (Cd, Hg)Te systems according to which the solubility of ZnTe in SnTe is of the order of 1.5 mol%, while that of CdTe amounts to 6 mol% and that of HgTe is 1.5 mol%.Specimens of appropriate geometry were prepared from ingots after annealing. the numerical value of electric conductivity being decreased with growing molecular weight of the component dissolved (Fig. 1).The dependence of the thermoelectromotive force (6) on the composition shows a weak minimum at a CdTe and HgTe content equal to 1 mol% and decreases continuously with growing concentration of ZnTe (Fig. 2).Just like the electric conductivity the total heat conductivity % drops with increasing per cent content of telluride A", the decrease in system being more substantial than that for the SnTe-Cd (I3g)Te system (Fig. 3).The concentration and mobility of current carriers calculated as p* = l/eRx and u = R d have extreme values at a 1 molg content of A Te in the composition range investigated (Fig. 4). In this case the concentration of current carriers which depends slightly on the composition shows a minimum, while the mobility of current carriers which according to its numerical values is more dependent on the composition displays a maximum. The results obtained in studying thermoelectric parameters may be explained on the basis of the double-valence-band model developed elsewhere (1 to 3, 6, 7) for de and Sn tellurides (it is retained in the solid solution region under study) and by the defective nature of the crystal lattice of the solid solution. The apparent mobility of current carriers is maximum when the content of the second-group tellurides is 1 mol%. As the per cent content of the

The initial compounds of the GeTe-GaTe system are hown to be %nperfect" semiconductors (1, 2).To get more detailed information on the behaviour of flimperfecttl structures it is interesting to study the constitution diagram of this system by the ultrasonic method. That is why this paper is concerned with the investigation of the dependence of the ultrasonic wave propagation velocity on the concentration of components in the GeTe-GaTe system.To this aim alloys were synthetized in evacuated (to Torr) quartz ampoules.The furnace where the ampoules were placed was held at a temperature of 1100 "C during 5 to 6 h. The alloys were cooled down in the furnace. Then the specimens were annealed at 200 "C during 200 h which was sufficient to homogenize them.They were prepared in the form of small cylinders with diameters of = 12 mm and lengths of ss 15 mm and subjected to plane-parallel surface grinding.The propagation velocity of longitudinal ultrasonic waves was measured at a frequency of 1.67 MHz and at room temperature by the relative pulse method to an accuracy of 0.5%.The dependences of both the propagation velocity and the attenuation coefficient of ultrasonic waves on the composition are shown in Fig. 1. The value of the ultrasound velocity grows as the GaTe content of GeTe increases up to 6 mol%, and above this limit it begins to decrease.The ultrasonic attenuation has been measured at 7 MHz by the pulse method.The value of the attenuation coefficient for the system decreases as the GaTe content grows to 8 to 10 mol%. This is due to the decrease of sound energy scat-

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