Brillouin scattering and molecular dynamics study of the elastic properties of Pb(Mg1/3Nb2/3)O-3

We report the complete set of elastic constants and the bulk modulus for single-crystal Pb(Mg1/3Nb2/3)O-3 (PMN) at room temperature obtained from Brillouin spectroscopy and molecular-dynamics (MD) simulations. The bulk modulus from Brillouin spectroscopy is found to be 103 GPa, in good agreement with earlier x-ray studies. We also derived the refractive index along all principal axes and found PMN to be optically isotropic, with a refractive index value of 2.52 +/- 0.02. PMN shows elastic anisotropy with A=1.7. The MD simulations of PMN using the random site model overestimate the elastic constants by 20-50 GPa and the bulk modulus of 148 GPa, but the elastic anisotropy matches the Brillouin results of A=1.7. We also determined the elastic constants for various models of PMN and we predict variation in the elastic constants based on chemical ordering.