3D-XRD: 3-dimensional maps and dynamics of grains
Henning Friis Poulsen, Lawrence Margulies, Erik Mejdal Lauridsen, Søren Schmidt, S. F. Nielsen, Grethe Winther · Acta Crystallographica Section A Foundations of Crystallography · 2002
Seven new Ba borates, namely Ba2[B5O9]ClO0.5H2O (I), LiBaB9O15 (II), Ba2[B5O8(OH)2](OH) (III), Na2Ba2[B10O17(OH)2] (IV), LiBa2[B10O16(OH)3] (V), Ba5[B20O33(OH)4]H2O (VI) and Ba[B5O8(OH)]H2O (VII) were recently synthesized and studied by XRD.The topology of the borate frameworks and sheets in I-VII may be described by means of the fundamental building block (FBB) consisting of BO3 triangles and BO4 tetrahedra.FBB in I (3BO4 tetrahedra and 2BO3 triangles) is the same as compared with that revealed in hilgardite.In contrast to I 3-membered polyhedral rings composed of 2BO3 triangles and 1BO4 tetrahedron can be considered as FBB within the framework of II.II comprises borate framework with the tunnels filled by Ba atoms in 12-fold coordination and by Li atoms in unusual 3-fold coordination.III is a sheet borate: its pentaborate [B5O8(OH)2] 3-sheets are characterized by the same ratio between BO4 tetrahedra and BO3 triangles as compared with the pentaborate framework in I. IV also contains pentaborate FBB formed by 3 tetrahedra and by 2 triangles.Two pseudohexagonal sheets in IV form the double layers, which are connected by Ba-and Na-polyhedra.V is characterized by new borate sheet, which is formed by 5 unequivalent BO4 tetrahedra and by 5BO3 triangles.Two pentaborate groups are included in its FBB.One of them comprises 3 borate triangles and 2 borate tetrahedra, whereas the second one is formed by 3 borate tetrahedra and by 2 borate triangles.Similar FBB were recognized in double borate sheets of VI.However in contrast to V, in VI two adjacent layers are related by 2-fold axes to form a double borate sheets.The topology of the borate sheet of VII is practically the same as compared with that revealed in beringuccite, Na2[B5O8(OH)]H2O, where FBB is formed by 3BO3 triangles and by 2BO4 tetrahedra.The interlayers in Ba-beringuccite and Na-beringuccite contain the Ba atoms and water molecules.Similarly with most of natural borates all studied structures contain threemembered borate rings formed either by 2 tetrahedra and 1 triangle or by 2 triangles and 1 tetrahedron.