Phenomenological Theory of Phase Change from FCC to FCT in the Indium Alloy

Abstract

In–Tl alloy transforms from fcc to fct when the Tl composition becomes lower than about 23 at%. In the In–Hg and the In–Pb alloys, fcc, fct(c⁄a>1) and fct(c⁄a<1) phases appear and the axial ratio (c⁄a) is dependent on the electron atom ratio. These phase changes in the indium alloys are treated by the phenomenological theory based on the Landau’s theory of phase transition, by assuming that the elastic constant (C₁₁−C₁₂)⁄2 of the fcc phase is directly proportional to composition m and becomes zero at m=m₀. As a result, composition dependences of the axial ratio (c⁄a) and (C₁₁−C₁₂)⁄2 in both fcc and fct phases are well explained phenomenologically.