The structure of the high-temperature RbB3O5 modification (T = 293 K) has been solved by the direct method and refined in the approximation of anisotropic atomic thermal vibrations to R = 0.065. The parameters of the orthorhombic unit cell are a = 8.438(6), b = 8.719(4), and c = 6.240(3) ?; V = 459.1(8) ?3; Z = 4; sp. gr. P212121; Dcalc = 2.863(5) g/cm3. The structure forms a new structure type and consists of a three-dimensional boron-oxygen framework with the structural unit formed by a [BIII2 BIVO5]- ring consisting of two [BO3]-triangles and a [BO4]-tetrahedron. Being connected, these rings form helical chains along the symmetry axis 21 (parallel to the a-and b-axes) and infinite channels along the c-and a-axes in which Rb atoms are located around the symmetry axes. The thermal expansion of the structure is obviously anisotropic: ?a = 18, ?b = -11, ?c = 89.2, and ?v = 96 ? 10-6 ?C-1.
|Состояние||Опубликовано - 1998|