Lithium ordering in H [sbnd]LiTa 3O 8

Abstract

It has been found by electron and neutron diffraction techniques that the b axis of the orthorhombic unit cell of H LiTa 3O 8, determined by X-ray difraction, must be doubled in order to expalin all the reflections. The new space group is Pmmn with eight molecules per unit cell of dimensions :a = 16.718, b = 7.696, c = 8.931 A. A structural refinement, based on reflections measured by a four-circle neutron diffractometer on a single crystal, gave the position of all atoms, including the lithium ones. The ordering of the latter atoms is responsible for the doubling of the b axis. They do not contribute much to the stability of the structure, but are mainly needed to balance the electrostatic charge. The weak Li O bonding is responsible for the large thermal vibrations of the lithium atoms and for the ionic conductivity of H LiTa 3O 8 at higher temperatures.