Study of Lattice Instability by mm‐Wave Magnetoplasma Reflection in PbTeSnTe Compound Semiconductors

The static dielectric constant ϵs in Pb1−xSnxTe (x = 0 to 0.4) single crystals is determined from a magnetoplasma reflection measurement between 4.2 and 100 K. At high temperatures ϵs increases with increasing temperature obeying a Curie law. The Curie constant is practically unchanged for different alloy composition, and the inverse static dielectric constant at 4.2 K decreases lineaarly with x, going to zero at alloy composition x = 0.35. At x = 0.40, a phase transition is observed at 20 K. The temperature dependence of ϵs is explained by anharmonic terms of lattice vibrations.