Measurement of the elastic constants of argon from 3 to 77 degrees K

The velocity of sound has been measured in argon single crystals by the pulse-echo technique for both longitudinal and transverse waves from 3 to 77 degrees K. The values of the elastic constants obtained by extrapolation of the results to 0 degrees K are: c 11 =4.39, c 12 = 1.83 and C 44 =1.64, in units of 10 9 N m -2 . Comparison with several lattice dynamical models indicates that models incorporating only central two-body forces are inadequate. New values for the adiabatic bulk modulus permit more accurate calculation of the Debye characteristic temperature and the Gruneisen parameter.