The 193 k phase transition in RbCaf3 : II. critical neutron scattering

Abstract

High resolution inelastic neutron scattering constant Q scans have been performed near the 193 K cubic (O1h) to tetragonal (D184h) phase transition in RbCaF3. A divergent temperature dependent central peak was observed at q = qR. The parameters λ1, λ2 and λ3 characterizing the anisotropy of the dispersion map in the vicinity of the R 25 mode have been measured at different temperatures. Taking into account the large anisotropy of the dynamical structure factors of the 3 modes belonging to the R25 soft mode, the 4 unknown parameters (A, ω2∞, Γ, δ2 ) of the spectral response used by Shapiro et al. in SrTiO 3 were determined by fitting the calculated scans with the experimental ones. The temperature dependence of ω2∞ et δ 2 is reported ; δ2 is found to decrease when (T - Tc) increases. The validity of the q and T dependence of the spectral response function is discussed on the basis of our results