Mass and force-constant disorder in the rocksalt Cd1-x Znx O alloy: A Raman scattering study

We present a Raman scattering study of rocksalt Cd1-xZnxO alloys in the compositional range between x = 0 and x = 0.1. We use the sharp feature in the second-order Raman spectra associated with the transverse acoustic (TA) modes at the L point to monitor the effect of alloy disorder on the phonon lifetime. The 2TA(L) peak shows a substantial broadening as the Zn content is increased up to 10%. The rate of increase is significantly higher than that expected from cationic mass fluctuation as predicted by the mean-field coherent potential approximation. Excellent agreement with the experiment is achieved by including the effect of the force-constant fluctuations using the itinerant coherent potential approximation, demonstrating the significant role of the force-constant disorder in limiting the phonon lifetime in the Cd1-xZnxO alloys.