Lattice instability and phonon lifetimes in Pb1-xSnxTe alloys

Neutron elastic and inelastic scattering studies have been made on single crystal samples of Pb1-xSnxTe (x=0.13, 0.20). Soft mode and Bragg peak intensity measurements gave no indication of the occurrence of a displacive phase transition. The energy widths of the soft TO phonons were observed to be strongly temperature dependent, ranging from approximately zero at liquid helium temperature to about 0.5 THz at room temperature.