Characterization of phases in the 50-60 at. % Te region of the Bi-Te system by X-ray powder diffraction patterns

Samples in the Bi-Te system containing 59.0, 58.0, 57.0, 55.0, 51.0, and 50.0 at.% Te, in addition to 5 samples within the Bi₂Te₃ homogeneity range, have been equilibrated near 525 or 450°C and room temperature powder diffraction patterns taken. There are now 4 known phases in the 50-60 at.% Te region. The 59.0 and 58.0 at.% samples are two phase at 525°C. The 57.0 and 55.0 at.% samples are new phases with hexagonal parameters, a = 4.4106±0.0002 Å, c = 54.330±0.003 Å and a = 4.4214±0.0004 Å, c = 78.195±0.012 Å, respectively. The 51.0 and 50.0 at.% samples are two-phase at 525 C. At 450°C the 51.0 at.% sample is single phase while the 50.0 at.% sample probably is not. The common indexing scheme for the 50.0 and 51.0 at.% samples is different from those for the 55-0 and 57.0 at.% samples. For the 51.0 at.% sample a = 4.4296±0.0002 Å and c = 24.017±0.001 Å. The 00l lines for all these phases vary strongly with composition and those near d = 9 and 5 Å are isolated enough to provide a convenient way of distinguishing among the various phases. The results are discussed in terms of other phase-diagram information. They are inconsistent with Stasova's correlation between composition and powder-pattern indices for the Bi-Te, Bi-Se, and Sb-Te systems.