Elastic constants of krypton single crystals determined by Brillouin scattering

Abstract

Single crystals of krypton were grown at 115.6 K; Brillouin spectra of two such crystals were investigated for several orientations. All three Brillouin components expected for a cubic crystal were observed and their frequency shifts were used to evaluate the adiabatic elastic constants: ${C}_{11}=26.57\ifmmode\pm\else\textpm\fi{}0.30$,${C}_{12}=17.25\ifmmode\pm\else\textpm\fi{}0.20$, ${C}_{44}=12.61\ifmmode\pm\else\textpm\fi{}0.15$, in kbar. These values lead to an adiabatic bulk modulus ${B}_{S}=20.36\ifmmode\pm\else\textpm\fi{}0.22$ kbar, and to an anisotropy parameter $A=2.704\ifmmode\pm\else\textpm\fi{}0.013$. The available theoretical values, whether based on a Mie-Lennard-Jones (6-12) potential or on a more refined pair potential, are not in agreement with the present elastic constants. A comparison of these values with the elastic constants determined from recent neutron-scattering experiments shows differences as large as 12%. It is suggested that these differences arise from the different velocities of zero and first sound in this temperature region of large anharmonicity. An analysis of the relative intensities of the Brillouin components yielded the ratios $\frac{{p}_{12}}{{p}_{11}}=1.00\ifmmode\pm\else\textpm\fi{}0.08$ and $\frac{{p}_{44}}{{p}_{11}}=0.11\ifmmode\pm\else\textpm\fi{}0.01$ for the Pockel's coefficients.