Phase transitions in RbCaF3

The temperature dependence of the structures of RbCaF3, and the determination of the low temperature phases

“…Moreover, according to refs. [13] and [16] new phases appear at low temperature (phase transitions near 50 K and 7 K) whose structures are reported in this paper. The importance of the determination of these structures comes from the possibility to check different models forecasting them.…”

“…Transitions such as those discussed above are Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphys:0198000410108700 encountered in RbCaF3, in particular the 193 K (1) transition (Oh to D4h18) [13,14]. Moreover the additional presence of a central peak in the cubic phase [15] increases the interest of the Debye-Waller factor and tilt angle determination in this compound.…”

Raman scattering study of the high-temperature vibrational properties and stability of CaGeO3 perovskite

“…These transitions are central to the rich phenomenology displayed by perovskite-type compounds and have been extensively investigated in SrTiO3 (Fleury et al 1968;Cowley et al 1969;Shirane and Yamada 1969), KMnF3 (Gesi etal. 1972;Lockwood and Torrie 1974), and RbCaF3 (Modine et al 1974;Berger et al 1978;Boyer and Hardy 1981) perovskites. Typically, antiferrodistortive transitions in these compounds occur with increasing temperature through critical soft-mode behavior where one or more vibrational modes, associated with oscillations of the octahedral rotational degrees of freedom, vanish at the transition temperature.…”

Application of Fission Chamber to Uranium Microanalysis

“…This transition was shown to be structurally identical to the archetype perovskite SrTiO 3 [6] and related to the softening of the triply degenerate R 15 eigenmode located at the R(0.5, 0.5, 0.5) point of the first cubic Brillouin zone. The second transition occurring at T c = 31.5 K [4,5,7,8] gives rise to an orthorhombic symmetry without any group-subgroup relation with the tetragonal one and then this transition shows a first order character. In the case of KCaF 3 , two SPTs were previously observed at high temperature [9][10][11][12]: the first at 560 K is due to the simultaneous condensation of eigenmodes located at the R(0.5, 0.5, 0.5) and M(0.5, 0, 0.5) points of the cubic Brillouin zone and the last occurring at 551 K is associated with an additional condensation of one component of one eigenmode at the R(0.5, 0.5, 0.5) point of the cubic reciprocal space.…”

“…Actually RbCaF 3 exhibits a first phase transition at 198 K [4] giving rise from the ideal cubic perovskite structure (see figure 1) to a tetragonal symmetry, corresponding to alternate rotations of CaF 6 octahedra around one of the major cubic axes (see for instance the review of Daniel et al [5] and references therein). This transition was shown to be structurally identical to the archetype perovskite SrTiO 3 [6] and related to the softening of the triply degenerate R 15 eigenmode located at the R(0.5, 0.5, 0.5) point of the first cubic Brillouin zone.…”