A NEW SUPERSTRUCTURE IN (LiXAg1-X) NbO3 (0.05 < X < 0.10)

Abstract

LixAg1-xNbO3 (0 ≤ x ≤ 0.10) compositions have been fabricated by the mixed oxide route to study the effect of Li on the host material, AgNbO3. The main X-ray diffraction (XRD) traces for ceramics with x < 0.10 were single phase and could be indexed according to the orthorhombic, Pbcm, structure, √2ap×√2ap×4ap (where ap = pseudocubic perovskite lattice parameter). For composition with x = 0.1, extra peaks, attributed to LiNbO3, were observed, accompanied by phase transformation to the rhombohedral, R3c, structure. The same phase change was also revealed by Raman scattering and electron diffraction but the latter technique revealed reflections for x = 0.1 at ±1 /6{00l} and ½{ooo}±1 /6{00l} (where o = odd). Previous investigations (Nalbandyan et al. 1980, Sakabe et al. 2001, Fu et al. 2008) report that Li- content > ~ 0.06 had hombohedral, R3c, symmetry and a - a - a - tilt system evidenced by reflections at ½{ooo} positions. Nevertheless the present study supports the premise that Li doping 0.05 < x < 0.1 causes a new modulated tilt system with a √2ap×√2ap×6ap. This phenomenon is also reflected by the strong asymmetry in the M3–M2 dielectric anomaly. Slim polarisation versus field loops were observed indicating remanent polarisations that went up as a function of increasing Li-concentration albeit under subcoercive fields