Brillouin scattering investigation of the elastic properties of LaF_3′ CeF_3′ PrF₃ and NdF₃

Abstract

The behaviour of the zone-centre acoustic phonons has been investigated in LaF_3′ CeF_3′ PrF₃ and NdF₃ over a wide temperature range. It is shown that in spite of the trigonal structure of these crystals, their elastic properties can be well described with an approximation to hexagonal symmetry. The values of the elastic coefficients increase with increasing atomic number of the cations. The Debye temperatures were determined at temperatures from 80 to 560K with a typical value of θ _D = 385 K at 300 K.