The effect of Li-substitution on the M-phases of AgNbO3

Abstract

Ceramics in the solid solution, LixAg1-xNbO 3 (LAN) with 0 x 0.20, have been synthesized by the mixed oxide method. X-ray diffraction (XRD) revealed that only compositions with x 0.05 were single phase which were indexed according to Pbcm symmetry with a unit cell, 2ap × 2ap × 4ap (where a p is the fundamental perovskite lattice parameter). For compositions with x 0.1, second phase peaks attributed to LiNbO3 were observed and the matrix phase transformed to a metrically rhombohedral structure according to XRD. A phase transition at 0.05 x 0.1 was confirmed by Raman spectroscopy and electron diffraction but the latter technique revealed superstructure reflections for x 0.1 at ±1/600l and 1/2ooo ± 1/600l (where o odd). These support the premise that Li doping invokes a new complex modulated tilt system with a 2ap × 2ap × 6ap unit cell rather than 2ap × 2ap × 4a p (Pbcm). Reflections of the type ±1/600l are, however, streaked along the 001 direction indicating that the structure may be incommensurate or only partially ordered. The appearance of the 2ap × 2ap × 6ap structure is associated with strong asymmetry in the peak in permittivity attributed to the M 3-M2 and a decrease in intensity of the peak in permittivity associated with the M2-M1 transition. Slim polarization versus field curves characteristic of weak ferroelectricity were observed for compositions with x 0.05 but for higher values of x the loops were unsaturated albeit with larger remanent polarization. © 2012 American Institute of Physics.