Structure, thermal properties and phase transition in RbCdHfF7: experiments and lattice dynamics calculations
Bogdanov, E.V., Molokeev, M.S., Gorev, M.V., (...), Laptash, N.M., Flerov, I.N.// Solid State Sciences//
https://doi.org/10.1016/j.solidstatesciences.2025.108042
A mixed-cation fluoride RbCdHfF7 was synthesized. The room temperature structure was determined as orthorhombic (Cmcm, Z = 4). Comprehensive studies of thermal properties and permittivity revealed a phase transition of a non-ferroelectric nature at T0 = 207 K.
Calculations using the density functional theory, as well as the behavior of the order parameter Ω(T), indicate a doubling of the unit cell volume in the low-temperature phase, which is associated with an unstable mode at the S boundary point of the Brillouin zone. The monoclinic symmetry (P21/c, Z = 4) was chosen for phase below T0. Very high sensitivity to hydrostatic pressure and low entropy of structural transformation were found and discussed.