HOMOGENEITY RANGES AND TE2-PRESSURE ALONG 3-PHASE CURVES FOR BI2TE3(C) AND A 55-58-AT PERCENT TE PERITECTIC PHASE

The partial pressure of Te2, P2, has been determined for preannealed Bi-Te samples between 44 and 70 at.% Te and 400 and 635°C by measuring the optical density of the vapor between 7000 and 1990 Å. Values of P2 and 103 T were obtained along the three-phase curves of the Bi2Te3(c) phase and of a 55-58 at.% Te phase decomposing peritectically at 563 ± 2°C. The detailed liquidus line between 44 and 70 at.% and the solidus line for Bi2Te3 are obtained. The homogeneity range of the latter is roughly symmetrical about the ideal 60 at.% composition and is a maximum of about 0.4 at.% wide, between 460 and 520°C. Bi2Te3 melts congruently at 586.0°C and 59.95 at.% Te. It is shown that the antistructure model provides a nearly correct relationship between composition and carrier concentration in Bi2Te3. The P2 isotherms, however, deviate from mass-action law predictions. © 1969.