Pressure derivatives of the elastic constants of NaCl and KCl at 295°K and 195°K

Abstract

The pressure derivatives of the adiabatic elastic constants of NaCl and KC1 have been measured at 295°K and 195°K using the ultrasonic pulse-echo technique. The values found are: d C′ 11/d P d C′/d P d C 44/d P NaCl 295°K 7.24 4.79 0.37 195°K 7.03 4.76 0.32 KCl 295°K 6.83 5.61 −0.39 195°K 6.78 5.59 −0.42 where the notation C′ 11 = (C 11 + C 12 + 2C 44) 2 and C′= (C 11 − C 12) 2 has been used. The results were used to calculate mode gammas, denned by γ i = − dlnω i dln V where ω i is a normal mode frequency of the crystal lattice and V is the crystal volume. These ω i were found to have no strong temperature dependence. The mode gammas were suitably averaged to obtain values of Gruneisen's parameter which agree satisfactorily with those from the Mie-Gruneisen equation of state.