Composition stability limits for the rocksalt-structure phase (Pb1−ySny)1−xTex from lattice parameter measurements

The lattice parameters at 25°C have been measured on powders with a precision of one part in 3(104) for (Pb1−ySny)1−xTex for y = 1·0, 0·90, 0·80,and0·00 and values of x both without and, for the first threey-values, within the composition stability range. For the first threey-values, the composition stability limits for samples metal-saturated at 400°C is 0·5000 ± 0·0002, while those for samples Te-saturated at 356°C is x = 0·5070fory = 1·0, x = 0·5056fory = 0·90,andx = 0·5038fory = 0·80. The fine powders pick up oxygen quickly in air, which reacts with the Pb and Sn upon heating to deplete the telluride solid-solution of metal and consequently reduce its parameter by 2–3(10−3)Å. The metals are substantially all returned to the telluride phase upon H2-reduction at 500–600°C. The present results for SnTe are used to extend the sources of data used in an analysis of SnTe. This analysis shows that the ratio of the number of valence band holes per Sn-vacancy, c, to the 77°K Hall factor, r, is 3·2 ± 0·3 over the entire range of 3(1019) to 1·8(1021) cm−3 in the apparent hole concentration. The results for the solid solutions are extrapolated to give the atomic fraction of Te in the 356°C, Te-saturated solid solution for y < 0·8. Comparison with the electrical measurements of others gives c/r equal to about unity for y = 0·27and0·13.