Investigations of morphotropic phase transformations in the solid solutionof Bi4Ti3O12 and Bi2Ti4O11 accompanied by defect dipole orientation and oxygen vacancy migration

Nanopowders of Bi2Ti2O7 with various Na+ modifications were synthesized by chemical coprecipitation, and their phase structures transform into a solid solution of Bi4Ti3O12 and Bi2Ti4O11 after sintering at high temperature. T he dielectric peak at around 517 degrees C in Bi4Ti3O12 is related to the d omain transformation at 445 degrees C in Bi2Ti2O7 and at 468 degrees C in B i2Ti4O11 and moves to a higher temperature with increasing Bi2Ti4O11 concen tration in the solid solution. Consequently, a dramatic drop of dielectric value in the solid solution was observed under a direct current bias due to the loss of relaxation mechanisms originated from the defect dipole orient ation as well as oxygen vacancy migration. Furthermore, E-field dependent r esistive measurements in Bi2Ti4O11 ceramics at various temperatures assert the defect dipole rotation and oxygen vacancy migration in combination with macrodomain alignment inside grains. Especially around phase transition, t he field-induced phase switching leads to the abnormal jump of resistivity. Finally, the P-E hysteresis loop measurements show a good ferroelectricity in the solid solution. (C) 1999 American Institute of Physics. [S0021-8979 (99)07403-4].