Pressure Dependence of the Elastic Constants of TlCl

The adiabatic second-order elastic constants of TlCl and their pressure derivatives have been measured by means of the ultrasonic pulse echo method at room temperature in the pressure range up to 4,000 bar. The adiabatic second-order elastic constants, in units of 10 11 dyn/cm 2 , are: C 11 S =4.015±0.002, C 12 S =1.537±0.002, C 44 =0.7843±0.0004, and their pressure derivatives are: d C 11 S /d P =7.14±0.05, d C 12 S /d P =6.47±0.10, d C 44 /d P =2.54±0.05. The present results allow us to determine three linear combinations of the six independent third-order elastic constants, the coefficients of the Murnaghan logarithmic equation of state, the Debye temperature, and the mode Grüneisen parameters from which the low and high temperature limits of the Grüneisen constant are evaluated.