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

2014 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 03BB1, 03BB2 and 03BB3 characterizing the anisotropy of the dispersion map in the vicinity of the R25 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, 03C92~, 0393, 03B42) of the spectral response used by Shapiro et al. in SrTiO3 were determined by fitting the calculated scans with the experimental ones. The temperature dependence of 03C92~ et 03B42 is reported ; 03B42 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. LE JOURNAL DE PHYSIQUE TOME 38, NOVEMBRE 1977, Classification Physics Abstracts 63.20 64.70K