High-Temperature Crystal Chemistry of Cs- and Sr-Borosilicates

Thermal Expansion of Alkaline-Earth Borates

“…The anisotropy of deformations of the ac monoclinic plane is caused by the considerable change in the angle β and the related shear deformations as well as arranging 5B-groups. As it discussed before [4,19,79] in the case of structure with 5B-groups the internal oxygen and boron atoms of both single rings vibrate perpendicular to the planes of these rings, while the group as a whole oscillates relative to the axis of the 5B-group -the line drawn parallel to the plane of both rings. The maximum expansion occurs perpendicular to the axis of the group and the minimal expansion is along the axis of group.…”

“…The borates built by complex rigid groups expand dramatically anisotropically when the complex units contain more triangles than tetrahedra or their quantity comparable. In contrast, SrB4O7, composed of tetrahedra only, demonstrates almost isotropic thermal expansion due to the random distribution of the rigid B-O bonds in the crystal structure [4,23,57]; also, there is weak anisotropy in layered Sr3B14O24 and in a few borates where BO3 planes are depicted not in parallel and the amount of BO3 is not significant.…”

“…Selected characteristics of thermal expansion like eigenvalues of tensor, a11, a22, a33, volume TECs (aV = α11 + α22 + α33), the anisotropy parameters for 20 alkaline-earth borates are summarized in Table 1. Thermal expansion of these borates has been examined by high-temperature X-ray powder diffraction before [4,49,50,[56][57][58][59]67,70] and supplemented by the data from present work. Here, except for the formula of the compound, its symmetry (system and space group) and the reference of the source, the volume expansion coefficient equal to sum, degree of anisotropy thermal expansion are given.…”

“…Over the past few decades, newly discovered borates have been the focus of research due to their diversity and well known applications [1][2][3][4][5][6]. The crystal chemistry of borates is diverse because boron atom orbitals can hybridized to either sp 2 or sp 3 configuration forming BO3 or BO4-polyhedra in the same crystal structure.…”

Growth and characterization of Na3R(BO3)2 (R = La–Gd) borates: crystal structure, high-temperature behavior, and optical properties

“…The volume thermal expansion is relatively high (α V = 62.5(3) × 10 −6 °C−1 ) compared with pure sodium borates (〈α V 〉 = 50 × 10 −6 °C−1 ) and is closer to hydrated sodium borates. 47 According to the traditional principles of the hightemperature behavior of borates, their maximal thermal expansion is perpendicular to the plane of the BO 3 triangle, 48 while the BO 3 triangles themselves are considered as rigid units. Though the crystal structure of Na 3 Nd(BO 3 ) 2 contains two independent sites occupied by boron, i.e., there are two different BO 3 triangles, which are almost perpendicular to each other, the anisotropy of thermal expansion cannot be explained by the existence of BO 3 triangles only.…”