Solid solutions in the system Li,O-Ta,O,-(MnO);, Ann. Chim. Sci. Mat, 1998,23, pp. 229-232 INVESTIGATION OF NEW LiTaO,-RELATED SOLID SOLUTIONS IN THE TERNARY SYSTEM L&O-T%O,-(MnO), : CRYSTAL CHEMISTRY AND FERROELECTRIC PROPERTIES A. ASSANI’, M. ZRIOUIL’, B. ELOUADI’~’ Laboratoire de Chimie du Solide Appliquee, Departement de Chimie, Faculte des Sciences, Av. Ibn Batouta, B.P. 1014, Rabat, Maroc. * Departement de Chimie, Universite de La Rochelle, Avenue Marillac, 17042 La Rochelle Cedex 01, France. Summary : New solid solutions isotypic of LiTaO,, were isolated inside the ternary system Li,O-Ta,OS- (MnO),. X-ray crystallography has allowed to determine the expansion of their domains along various joins of the ternary diagram. The steady increase of the lattice parameters and unit cell volume, versus composition, was attributed to the size of Mr?’ cations. The latter seems to have more impact than the vacancies that could be created within the lattice. A dielectric study has shown that the ferroelectric Curie temperature is decreased whenever the composition is removed from pure LiTaO+ Resume : Investigation de nouvelles solutions solides isotypes de LiTa03 a l’interieur du s&me temaire L&O-Ta,05-(MnO), : proprietes cristallochimique et dielectrique. De nouvelles solutions solides isotypes de LiTa03 ont Cte isolCes au sein du systeme temaire Li,0-Ta,05-(Mn0)2. L’analyse radiocristallographique a permis de dklimiter leurs larges domaines d’existence sur de nombreuses droites du diagramme temaire. L’augmentation systematique des parametres cristallins et du volume Gmentaire en fonction de la composition a tte attribu@e a la taille du cation Mn*’ qui semble l’emporter sur les lacunes qui pourraient &tre c&es dans le reseau. Une etude dielectrique a montre que la temperature de Curie ferroClectrique decroit, le long de toutes les solutions solides examinees, au depart du point limite LiTaOj. 1. INTRODUCTION Owing to their effective and potential technological applications, lithium niobate and tantalate are still subject to intense investigations since many decades (l-23). Interest in LiNbOJ has particularly grown since Franken et al. have succeeded to generate a second harmonic of a ruby laser radiation, using a quartz crystal (24). It was also shown that both the stoichiometry and the cationic distribution within the lattice network of LIMOS (M=Nb, Ta), play important roles in the control of the evolution of their physical properties: ferroelectric Curie temperature, photorefractive effect, etc (l-3, 13, 23). In previous investigations we have Reprints: A. ASSANI, L.C.S.A, Dkpartement de Chimie, Fat. des Sciences, B.P. 1014, Rabat, Maroc