Observation of multiple dielectric relaxations in BaTiO_3- Bi(Li_(1/3)Ti_(2/3))O_3 ceramics

摘要

Dense (1-x)BaTiO_3-xBi(Li_(1/3)Ti_(2/3))O_3 ceramics were fabricated by the solid state reaction route. Powder X-ray diffraction analyses revealed an increase in the unit cell volume with increasing x and a change on the average crystal structure from tetragonal (space group P4mm) to cubic (Pm3m) at x>0.10. Raman spectroscopy analyses corroborated a change of symmetry, but also showed the local structure for x> 0.10 to be inconsistent with the cen-trosymmetric (Pm3m) space group. The dielectric measurements revealed for the first time, to our knowledge, a double relaxor behaviour in a BaTiO_3-based solid solution. Basically, with increasing x, the sharp ferroelectric anomaly at the Curie temperature (T_c) shifts towards lower temperatures until a relaxor-type response is observed, but simultaneously, another relaxation emerges above T_c. The first arises from poor coupling between polar nanoregions, whereas the later obeys the Arrhenius Law and may be associated either with a defect-dipole reorientation or a Skanavi-type mechanism.