Phase Composition of Samarium Niobate and Tantalate Thin Films Prepared by Sol-Gel Method

Abstract

INTRODUCTIONRecently, the lanthanide (Ln = La, Nd, Sm, Eu and Gd) orthoniobates LnNbO 4 (LnNO) and orthotantalates LnTaO 4 (LnTO) materials have been developed for wide applications in satellite communication systems [1]. Samarium niobate SmNbO 4 (SNO) and tantalate SmTaO 4 (STO) films can be used as phosphors for solid-state lighting, as photocatalysts in solid-state laser materials and as ion conductors for solid oxide fuel cells. Samarium niobate (SmNbO 4 ) and tantalate (SmTaO 4 ) with fergusonite structure have attracted a great deal of attention due to their interesting physical properties, such as high dielectric constants, electro-optical, photoelastic, photocatalytic and luminescent properties as well as good mechanical and chemical stability. For SNO, there are two crystalline forms, the low temperature M-phase isostructural with monoclinic form of the fergusonite and the high temperature T-phase corresponding to tetragonal scheelite. The transition between two phases occurs reversibly in the range 500-800°C [2]. STO crystallizes in monoclinic form, besides its ability to possess two fergusonite-type structures, first known as M-type (I2/a) and second called M´-type (P2/a) [1,2].