Investigation of the system LiZnV,,P,O, Ann. Chim. Sci. Mat, 1998,23, pp. 251-254 CRYSTAL CHEMICAL AND DIELECTRIC INVESTIGATION OF THE SYSTEM LiZnV,.,P,O, M. AZROUR, L. EL AMMARI, W. DEPMEIER*, B. ELOUADI** Applied Solid State Chemistry Laboratory, LAF, 501, Faculty of Sciences Charia Ibn Batota, Rabat, Maroc. * Mineralogisch-Petrographisches Institut und Museum der Universimt Kiel, Olshausenstr. 40. D-24098 Kiel, Germany. ** Departement de Chimie, Universite de La Rochelle, Avenue Marillac, 17042 La Rochelle Cedex 01, France. Abstract: An X - ray crystallographic study has allowed us to identify a solid solution of the type LiZrrV1,P,04 (05 x cO.6) inside the binary system LiZnVO4-LiZnPOd. The structure is isotypic with the phenacite like LiZnV04. X-ray diffraction patterns are indexed according to the lattice parameters of the trigonal systemand the spacegroup R3. The mother structure can be regarded as made of a three-dimensional network of LiO+ Zn04 and V04 tetrahedra all having one apex oriented along [OOl]. The peaks, observed on the curvesof the thermal variation of the dielectric constants,have allowed us to recognizea phase transition whose temperature variescontinuously along the solid solution. R&m&: Etude radiocrista~louraphinue du svstemeW&V,&& L’&ude radiocristallographique du systkme LiZnV04-LiZnP04 a permis de mettre en evidencela solution solide LiZnV1,P,O,, (05 x 20.6). La structure de tous les points est isotype a la structure phenacite de LiZnV04 qui cristallisedarts le syst&me trigonal avec le groupe d’espace R3. Cette structure est d&rite par un enchamement tridimensionnel des u&a&&s LiO+ Zn04 et V04 oriented selon la direction [OOl]. Les courbes de la variation thermique de la con&ante dielectriquemontrent despits de transition de phases. 1. INTRODUCTION. Most of the monovanadates with the formula LiM”VO4 (Mu= divalent cations) crystallizewith cubic or distorted spine1 structures (l-5). Analogous phosphates generally adopt the olivme structural type (Mg,Fe)Si04 (6-8). Other orthovanadates ArMnVO, (A’= Na, K and M = big size divalent cations) normally crystallize with NazCr04 or K2Cr04 structures while equivalent phosphates are mostly found with either olivine, A-KzS04or glaserite structural types (8-13). Furthermore, LiZnV04 crystallizing with a phenacite structure (Trigonal symmetty with space group R3 and lattice parameters: a = 14.1872 A; c = 9.48778 A, z = 18) under normal conditions,transforms to a spine1 polymorph (inversespine1 with space group Fd3m and a lattice parameter a = 8.31 A) when submitted to high pressure (1, 2, 14). LiZnPOd undergoestwo phase transitions(15): one at 728’C and the other at 995°C. At the time we started our program of research only one Reprints: L. EL AMMARL LCSA Departement de Chimie , Fat. SC. B. P: 1014. Rabat : Morocco.