Gammahyphen;lithium iodate structure at 515 K and the agr;hyphen;LiIO3to ggr;hyphen;LiIO3, ggr;hyphen;LiIO3to bgr;hyphen;LiIO3phase transitions

摘要

The crystal structure of ggr;hyphen;LiIO3at 515 K has been determined by profile refinement of xhyphen;ray diffraction powder data measured with a Hauml;ggndash;Guinier focusing camera. The space group isPna21, with lattice constants at 515 K ofa= 9.422(2),b= 5.861(2), andc= 5.301(2) Aring;. A model was derived from the Patterson function and by similarities with the agr;hyphen;LiIO3structure and refined by the method of least squares. For all 59 reflections resolved by the profile refinement method,RF= 0.109. The structural rearrangement at the agr;hyphen;LiIO3to ggr;hyphen;LiIO3phase transition involves ionic displacements of about 0.5 Aring;, with consequent rotations of the iodate ion by about 20deg; and elongation of the oxygen octahedron about the Li+ion. The symmetry change from point group 6 tomm2 is accompanied by unit cell doubling and an increased separation between layers of iodate ions normal to lsqb;100rsqb;. A further unit cell doubling occurs at the ggr;hyphen;LiIO3to bgr;hyphen;LiIO3phase transition, with reorientation of iodate ions to form inversion centers and tetrahedral interstices about the Li+ions.