The crystallography of some M2+ borates

Abstract

As part of a research program aimed at achieving a better understanding of the structural principles of borate crystals and glasses, crystallographic studios of an_hydrous borates have been undertaken. Crystals of barium, strontium and a lead borate were prepared from the melt. The cell dimensions* and space group of the MO.2B20 a types are: BaO. 2B~O a a ---10.56±0.01/~ fl = 104 ° 57' + 10' b = 8.20±0-01 S.G. = P21/c c = 13.01±0.01 Z = 8 This structure has been completed with partial three-dimensional data. The present reliability index R = 0.081. As soon as the refinement is finished, complete details of the structure will be reported. The structure consists of a three-dimensional boron-oxygen network. Half of the borons are in threefold coordination and half are fourfold. The network is composed of six-membered rings. The rings are of two types. One type is a single ring of the type found in Cs20.3BaO 3 (Krogh-Moe, 1960). To each of the outside oxygen atoms, a double ring of the type found in K20.5B~O a (Krogh-Moe, 1959) is connected. The barium atoms are in channels parallel to the b axis in this network. Table 1. X-ray diffraction powder pattern for SrO. 2B20 a d I/I o hkl