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b)Es wurden die thermischen Eigenschaften (Temperaturleitzahl, spezifische Warnie und Warmeleitung) des ZnTe, HgTe und HgSe, bei Temperaturen von 20 bis 540 O C fur ZnTe und von 20 bis 240 "C fur HgTe und HgSe untersucht. Die Messungen wurden a n Einkristallen ausgefuhrt, die nach dem Bridgman-Verfahren aus hochgereinigten Elementen hergestellt worden w-aren.Pie Bnalyse der Temperaturanderung der Gitterwarmeleitfaiiigkeit zeigte, daB sie im Falle des ZnTe durch Umklapp-Prozesse zu erklkren sind, dagegen muB bei HgTe und HgSe auch die Streuung der akustischen Phononen an den optischen Phononen und den Stronitragern in Betracht gezogen werden.

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BYAlthough the existence of the compound Tl Te has been proved a s early as 2 3 1960 (l), its optical or photoelectric properties have not been investigated so far. This is due, to a great extent, to the difficulties encountered in the preparation of large and homogeneous Tl Te crystals, taking into consideration that this compound is formed by a peritectic reaction.The electric properties of T1 Te have been reported for the first time in (1) 2 3 2 3where,based on electric conductivity and Hall effect measurements at 93 and 293 Kthe compound was found to be a semiconductor. Flicker and Grass (2) determined from the temperature dependence of electric conductivity that the thermal energy gap of Tl Te is 0.20 eV. In the same year, Ahmedova and Piragas(3)based on electric conductivity and Hall effect measurements, carried out between room temperature and close to the peritectic reaction temperaturefound the thermal energy gap of Tl Te to be 0 . 5 eV. 0 2 3 2 3 In indentifying T1 Te Rabenau et al. (1) determined the crystal lattice to be 0 2 3'base-centered monoclinic, with a = 1 3 . 5 x, b = 6 . 5 x, c = 7 . 9 x, and = 73 .Since information concerning the optical energy gap of T1 Te is not available in the literature, the present work was undertaken to fill this void. 3The optical measurements were carried out on single-crystal specimens, grown from the melt (4) starting from high-purity elements, supplied by Johnson Matthey and Co. Ltd. In order to prevent the oxidation of thallium, it was handled and weighed in a tight glovebox, in a current of plrified argon.were p-type with the concentration of charge c a r r i e r s of about 5 x 1 0~~ cm at 77 K (4). The specimens for optical measurements were 18 mm in length and 5 mm in width and the thickness varied between 150 to 340 pm. Both reflection and optical transmission were measured on finely ground and polished specimens. AdditionalThe Hall effect and thermoelectric power measurements showed that all samples 3 0