Abstract
Ceramics in the solid solution, LixAg1-xNbO3 (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, root 2a(p) x root 2a(p) x 4a(p) (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 +/- 1/6{00l} and 1/2{ooo} +/- 1/6{00l} (where o = odd). These support the premise that Li doping invokes a new complex modulated tilt system with a root 2a(p) x root 2a(p) x 6a(p) unit cell rather than root 2a(p) x root 2a(p) x 4a(p) (Pbcm). Reflections of the type +/- 1/6{00l} are, however, streaked along the inverted right perpendicular001inverted left perpendicular direction indicating that the structure may be incommensurate or only partially ordered. The appearance of the root 2a(p) x root 2a(p) x 6a(p) structure is associated with strong asymmetry in the peak in permittivity attributed to the M-3-M-2 and a decrease in intensity of the peak in permittivity associated with the M-2-M-1 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. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3677871]