The crystal structures of the quaternary system, (Bi
1-xSb
x)
2(Te
1-ySe
y)
3 with 0_??_
x_??_1 and 0_??_
y_??_1, were investigated by X-ray methods. 121 preparations were prepared by the direct reaction in a vacuum at 800°C from the molten state using the purest elementary substances, Bi, Sb, Te and Se each of 99.99% purity. The products were subjected to quenching by plunging them into water. X-ray observations show that the majority of the preparations belong to the rhombohedral system
R3m and the rest belong to the orthorhombic system
Pnma in addition to some which show to be a mixture of the two phases, both rhombohedral and orthorhombic. The lattice constants and densities and the ratios ρ
bulk/ρ
x-ray are measured for all the preparations. The lattice constants of the rhombohedral preparations, when expressed in the hexagonal unit cell
aH and
c, H, and the corresponding densities are found to be expressed by the following equations.
aH(Å)=4.38-0.135
x-0.23
y cH(Å)=30.5+0.125
x-1.7
y ρ
H(g/cm
3)=7.86-1.32
x-0.12
y-0.4
xy These equations can be used to determine the compositions of the quaternary system, Bi-Sb-Te-Se with fair accuracy.
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