Anharmonicity in CuCl—elastic, dielectric, and piezoelectric constants

Measurements have been made of the pressure and temperature dependence of the elastic, dielectric, and piezoelectric constants of cuprous chloride. Both shear elastic constants decrease with pressure with the $\frac{(c_{11}-c_{12})}{2}$ shear mode having the largest mode $\gamma$ of -1.9. The piezoelectric constant increases 12% at a pressure of 10 kbar. The negative thermal expansion at low temperature is explained by the softening of all shear acoustic modes with pressure.