Lithium-induced phase transitions in lead-free Bi0. 5Na0. 5TiO3 based ceramics

Lithium-substituted 0.95[0.94(Bi_0.5Na_(0.5-x)Li _x)TiO₃-0.06BaTiO₃]-0.05CaTiO₃ materials include the polar rhombohedral R3c and the weakly polar tetragonal P4bm phases. On increasing lithium content, the (R3c/P4bm) phase ratio decreased, while the rhombohedral and tetragonal lattice distortions remained the same. The temperature corresponding to the shoulder in the dielectric permittivity shows no clear shift with respect to lithium substitution because of the rhombohedral distortion remaining constant. Electrical poling produced an increase of the rhombohedral phase fraction together with a rise of the rhombohedral and tetragonal distortion. This confirmed the occurrence of a phase transition from the weakly polar to the polar phase during electrical poling. Four peaks found in the current-electric field (I-E) loops are related to reversible electric field induced transitions. By studying the temperature dependence of the current peaks in the I-E loops, it was found that the minimum temperature where these electric field induced transitions take place decreases with increasing lithium substitution.