Role of lattice distortion on diffuse phase transition temperatures in Bi_(0.5)Na_(0.5)TiO_3-BaTiO_3 BNBTO solid solutions

摘要

Effect of lattice distortion on diffuse phase transition in BNBTO solid solutions near Morphotropic phase boundary (MPB) has been investigated. Solid Solutions of (Bi_(0.5)Na_(0.5))_(1-x)Ba_xTiO_3 (with mole % of x=0.04, 0.05, 0.06, 0.07 and 0.08) were prepared by the planetary ball mill method in ethanol medium. Rietveld refinement technique with rhombohedral (R3c) and tetragonal (P4bm) crystal symmetry has been employed for structural as well as phase analysis of the solid solutions. Both rhombohedral and tetragonal lattice distortion (c/a) tends toward the pseudo-cubic crystal symmetry with the increase of mole fraction of Ba~(2+) near MPB (x= 6 mole %). Also, the average crystallite size and grain size decrease with increase of mole fraction of Ba~(2+) in BNT ceramic are due to larger ionic radius of Ba2+ and grain boundary pinning process in the solid solutions respectively. Additionally, depolarization temperature (T_d) and maximum temperature (T_m) reduces due to the lattice distortion of both the phases in BNBTO solid solutions, which is explained extensively. Significant increase of dielectric constant has been observed near MPB composition (x=6%) in BNBTO solid solutions.