Phase studies on the quasi-binary thallium (I) telluride-cadmium telluride system
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Phase Studies on the Quasi-Binary Thallium (I) Telluride-Cadmium Telluride System W. Gaweł, Z. Sztuba, A. Wojakowska, and E. Zaleska
(Submitted 9 March 2001) The phase diagram for the system Tl2Te-CdTe has been constructed from the results of studies by thermal analysis and x-ray diffraction (XRD). The diagram is compared with that published earlier as well as with predictions based on molecular stability ratios.
1. Introduction The present work is a part of a series of our studies on phase equilibria in the quasi-binary thallium (I) telluridemetal telluride “family” of systems (Tl2Te-MxTey , where M is any metal). The tellurides of metals are salts (of the hydrotelluric acid) and they embody some properties of salts, e.g., brittleness (lack of ductility), which is the most visible feature of thallium telluride (Tl2Te). Moreover, it may be assumed that the ionic contribution to the chemical bonding in Tl2Te is quite substantial [1971Nak] because of the considerable difference in electronegativities of thallium and tellurium. The Tl-Te binary system has been studied many times and the history of determining its phase equilibrium diagram is very interesting, as shown in [1997Rec]. At the same time, the mere existence of the compound Tl2Te has been questioned, not to mention the uncertainty concerning its congruent or incongruent melting. Our early electrochemical (by electromotive force measurements of concentration cells) studies [1965Ter] on the system Tl-Te also showed no existence of the compound. This resulted from the fact that the compositions of alloy electrodes in the earlier investigation varied by more than 0.5 at. pct Te; this exceeds the limiting condition [2001Zal] for measurements to be successful when studying systems of greater complexity. Strong evidence for the Tl2Te formation (congruently melting at 689 K) in the Tl-Te system was first obtained by Asadov et al. [1977Asa] (later confirmed in [1997Rec]). Since then, binary metal telluride systems have aroused the interest of many researchers because of the probability of ternary compound formation with possibility of semiconductive properties.
2. Former Data on the System Tl2Te-CdTe The system under consideration was first studied by Guseinov et al. [1981Gus], employing differential thermal analysis (DTA) and x-ray diffraction (XRD) methods. Based upon their results, a phase diagram for the system was proposed W. Gaweł, Z. Sztuba and E. Zaleska, Department of Analytical Chemistry; and A. Wojakowska, Department of Inorganic Chemistry, Faculty of Pharmacy, Wroclaw Medical University, Szewska 38, 50-139 Wroclaw, Poland. Contact e-mail: gaweł@bf.uni.wroc.pl.
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from which it followed that in the system no chemical compound was formed, the coordinates of the only eutectic being about 9 mol pct CdTe and about 650 K (Figure 1). The results were confirmed by the same authors [1984Bab].
3. Prediction of Compound Formation in the Binary Metal Telluride Systems From both our former studies on the Tl2Te-MxTey systems [1997Zal] and the literature, it foll
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