LI6P6O18 - X-RAY-POWDER STRUCTURE DETERMINATION OF LITHIUM CYCLOHEXAPHOSPHATE

Preparation, characterization by X-ray diffraction, IR absorption, DTA -TG analysis, and ab-initio crystal structure determination are report ed for anhydrous lithium cyclohexaphosphate Li6P6O18. It crystallizes in a monoclinic cell (space group P2(1)/n N degrees 14, Z=2) with a = 7.9911(3)Angstrom, b = 17.0319(6)Angstrom, c = 5.3208(2)Angstrom and p = 99.433(1)degrees. X-ray powder diffraction data were fitted by Riet veld method leading to R-Bragg = 0.034. The crystal structure of Li6P6 O18 is built up from P6O18 ring anions, with T internal symmetry. Six lithium coordination polyhedra (two pseudo square pyramids and four te trahedra) share common edges and corners as to form Li6O16 groups. The se cationic groups build up a layer in the (<1 0 (1)over bar>) plane s howing large distorted hexagonal tunnels and interconnect the P6O18 ri ngs in a three dimensional way.