Delectric properties of (Na0.5Bi0.5)(1-x)MexTiO3 ceramics near morphotropic phase boundary

Ceramic samples of modified ferroelectric sodium-bismuth titanate (Na0.5Bi0 .5)(0.87) Me0.13TiO3 (Me = Pb, Sr and Pb + Sr), were prepared using convent ional solid state reaction techniques. The studies of powder X-ray diffract ion of the obtained compounds revealed their rhombohedral symmetry at room temperature, the increase of lattice constant and the increase of rhombohed ral lattice distortion (except for the material with Sr dopand, where disto rtion decreases). Temperature (at room temperature to 400 degreesC) and fre quency (at 20 Hz to 1 MHz) dielectric measurements reveal that A-site catio ns addition of Pb and/or Sr have resulted in the increase of relative elect ric permittivity. However, the temperature T-m (when the electric permittiv ity is a maximum) increases after Pb or Sr doping and it decreases after (P b + Sr) doping. The pyroelectric and current loop measurements have shown t hat all samples were ferroelectric. The results of these measurements also allowed us to determine the temperature variation of the remanent and spont anous polarizations. The polarizations are found to decrease after Pb or Sr doping and increase after (Pb + Sr) doping. The piezoelectric constants (d (33) and d(31)) and electromechanical coupling factors (k(33) and k(31)) we re obtained from resonance-antiresonance measurements method. The best piez oelectric and electromechanical properties have NBT doped by Pb. This ceram ic may be good candidate for device applications. The diffuse ferroelectric phase transition of the investigated materials, similarly as for pure NBT, has been revealed. The properties of these materials (especially in diffus e phase transition range) can be explained by the behaviour of polar region s. (C) 2001 Kluwer Academic Publishers.