Crystal structure of the low-temperature modification of α-RbB3O5

Abstract

The crystal structure of α-RbB3O5 was refined by the Rietveld method with due regard for anisotropic vibrations of rubidium atoms to R p = 2.93, R wp = 3.80, R B = 2.53, R F = 2.84, and s = 1.54. The compound is isostructural to CsB3O5: it is orthorhombic, sp. gr. P212121, a = 8.209(1), b = 10.092(1), c = 5.382(1) Å, and V = 445.9 Å 3. The framework structure is formed by the boron-oxygen [B 2 III BIVO5] − rings consisting of two [BO3]-triangles and a [BO4]-tetrahedron. The rings are linked to form systems of helical chains running along the twofold screw axes parallel 21 to the a-and b-axes and infinite channels parallel to the a-and c-axes, which accommodate Rb atoms. The data were collected on an ADP-2 diffractometer [CuK α radiation, Ni-filter, 12.00° < 2θ < 110.00°, a step in 2θ equal to 0.02°, count time 8 s per step, and 711 reflections α1 + α2)]. All the calculations were performed using version 3.3 of the WYRIET program. The comparison of the structures of α-and β-RbB3O5 and CsB3O5 revealed that the type of deformations in the framework structures of alkali-metal borates due to the changes of the temperature or the substitution of cations is determined by the role played by metal atoms, and especially, by large and heavy ions.