The crystal structure of the high temperature form of barium borate, BaO.B₂O₃

Abstract

The crystal structure of the high temperature form of BaO.B203 (m.p. 1095 + 5C) was determined by conventional three-dimensional Patterson and electron-density syntheses. The heavy atom technique was used to establish the initial phases. BaO.B203 crystallizes in the trigonal system, space group R Sc, with 18 formula units per hexagonal cell. Unit-cell dimensions, referred to hexagonal axes, are a=b=7-235, c=39.192/~. Least-squares refinement with 498 independent reflections yielded a reliability index of 5.7 %, based on the observed data only. The anion in the structure is a nearly planar []3306] 3-group constructed of three BO3 triangles each of which shares two of the three corners. The structure contains two crystallographically distinct barium atoms located in positions having point symmetries 32 and 3. About the barium in the 32 point symmetry position the oxygens are arranged in a trigonal prism. About the barium which lies in the 3 point symmetry position the oxygen coordination is ninefold.