The structural properties of RbMnX3 (X=F, Cl, Br) halides

The results of nonempirical calculation of energies of three polytypes (cubic, two-layer hexagonal, and six-layer hexagonal) are given for RbMnX3 (X=F, Cl, Br) crystals. The calculation is performed using an ionic crystal model with regard for the deformability and the dipole and quadrupole polarizabilities of ions. The behavior of these crystals under the action of hydrostatic pressure is studied. It is demonstrated that, at normal pressure, the RbMnCl3 and RbMnBr3 crystals have a six-layer hexagonal structure. At pressures above 11 kbar, RbMnCl3 passes to a phase with a cubic structure; RbMnBr3 at pressures above 90 kbar passes to a phase with a two-layer hexagonal structure. The RbMnF3 crystal under normal conditions has a cubic structure and experiences no phase transformations under the effect of pressure. The obtained results are in satisfactory agreement with the known experimental data. (C) 2003 MAIK "Nauka/Interperiodica".