Temperature and pressure dependence of the transverse-optic modes of ionic crystals and their associated anharmonic self-energies

The temperature dependence (2-300 K) and hydrostatic pressure dependence (0-7 kbar) of the q≈0 transverse-optic mode frequency ωₜ and its associated damping 2Γ(0,t,ωₜ) are reported for the alkali, silver, and thallium halides. These results are analyzed to yield the temperature dependence of the thermal strain ΔE(0,t) and far-infrared anharmonic self-energies ΔTA(0,t,ωₜ) associated with the mode at ωₜ. In addition, calculations of ΔE(0,t), ΔTA(0,t,Ω) at Ω=0 and Ω=ωₜ, and Γ(0,t,ωₜ) are presented for the alkali halides crystallizing in the NaCl structure using current many-body thermodynamic Green's-function anharmonic theories, and these are compared with the experimental results.