On the issue of superstructure phase transitions in monoclinic RbD2PO4 crystal

This paper presents the results of group-theory analysis, lattice dynamics simulation and phenomenological treatment in three temperature phases of the monoclinic RbD2PO4. Combining the methods of group theory with the analysis of crystal structure peculiarities in different structural phases, it is shown that the lowest temperature phase should reveal a strict antiferroelectric state with P 21 symmetry rather than the ferrielectric state reported repeatedly. Lattice dynamics simulation was performed in the quasi-phenomenological approach comprising the Coulomb, short-range, covalent, van der Waals and hydrogen-bonded interactions. The probable mechanisms of phase transitions are considered.