Conductivity and Structural Investigations in Lacunary Pb6Ca2Li2(PO4)6 Apatite

Abstract Prismatic crystals of Pb 6 Li 2 Ca 2 (PO 4 ) 6 were obtained by solid-state reaction. They were characterized by IR spectroscopy and chemical analyses. The structure as determined by X-ray diffraction study on single crystal revealed that the compound is isostructural to the hexagonal phase Pb 8 Na 2 (PO 4 ) 6 . Crystal data for Pb 6 Li 2 Ca 2 (PO 4 ) 6 : space group P 63/ m (No. 176), a = b =9.6790(15) A, c =7.1130(7), Z =1, R =0.039. In the compound, lithium was found to preferentially occupy the site (I) and the structure is stabilized by interactions between electron lone pairs of lead (II) ions. Electrical conductivity measured in a wide range of temperature is governed by a hopping mechanism of Li ions in tunnels.