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Prawidłowości występujące w diagramach fazowych układów potrójnych Tl-Te-M

Sztuba Z.

Wiadomości Chemiczne

2009

[Z] 63, 9-10

803-818

The aim of this work was to present regularities in the phase equilibria in the Tl2Te-MxTey systems, where M stands for metals belonging to periods IV–VI and groups 11–15 of Periodical Table. Additionally, the Tl2Te-As2Te3, Tl2Se-Bi2Se3 and Tl2Te-Tl2Se systems were considered. The phase diagrams are presented in a simple form in Fig. 1 for the following systems: Tl2Te-Cu2Te [1], Tl2Te-ZnTe [2], Tl2Te-CdTe [3], Tl2Te-HgTe [4–6], Tl2Te-In2Te3 [7, 8], Tl2Te-PbTe [9], Tl2Se-Tl2Te [10], Tl2Se-Bi2Se3 [11], Tl2Te-Ga2Te3 [12], Tl2Te-Ag2Te [13], Tl2Te-SnTe [14], Tl2Te-Sb2Te3 [15], Tl2Te-Bi2Te3 [16], Tl2Te-GeTe [17] and Tl2Te-As2Te3 [18]. The state of phase equilibria illustrated by the phase diagram depends on the tendency to chemical compounds formation by the components of a system. This tendency can be observed in the number of compounds formed, their melting points and the type of melting process (congruent or noncongruent). The tendency to compounds formation or at least the melting points of the compounds formed increases with increase of the atomic number of the metal within a group of systems containing as the second component tellurides of metals from a given group in the Periodic Table. There is no correlation between type of phase diagram and metal position in a given period. Thus, increasing the number of outer shell electrons for consecutive elements M of the same group does not affect the tendency to the chemical compounds formation. Regardless of the compounds number – terminal solid solutions have been observed only in some telluride systems. The data in Table 1 show that solid solutions are formed when the value of relative difference between thallium and metal M radii is smaller than 10%. All salt systems arranged in decreasing order of their ionic potentials ratios μ_Tl/μ_M are presented in Table 2. While this ratio decreases the tendency to congruent compounds formation increases abruptly from 1 to 2 at the value of a ratio equal to 0.21, exactly as in the case of typical salts [20]. The influence of molecular stability coefficients on the number of compounds existing in the system (Table 3) has been discussed. The greater difference is between the values of molecular stability coefficients the more compounds are formed. The impact of a common anion change on the shape of phase diagrams for the systems Tl2Te-Bi2Te3 [16] and Tl2Se-Bi2Se3 [11] as well as the regularities in the chalcogenide systems with a common cation has been described. All compounds being components of the systems presented in this work are listed in Table 4.