Pressure Dependence of Elastic Constants and of Shear-Mode Instability inV3Si andV3Ge

Abstract

The pressure dependence of the single-crystal elastic constants of ${\mathrm{V}}_3$Si and ${\mathrm{V}}_3$Ge has been measured from 77 to 298°K. The first pressure derivative of the shear modulus $c_s=\frac{1}{2}(c_{11}-c_{12})$ is strongly temperature dependent and becomes negative at low temperature. For ${\mathrm{V}}_3$Ge, an abnormally large second pressure derivative of $c_s$ is found. The results are applied to the calculation of the microscopic and macroscopic Grüneisen parameters and to the pressure dependence of the structural transition in ${\mathrm{V}}_3$Si.