Investigations of morphotropic phase transformations in the solid solution of 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. The dielectric peak at around 517 degrees C in Bi4Ti3O12 is related to the domain transformation at 445 degrees C in Bi2Ti2O7 and at 468 degrees C in Bi2Ti4O11 and moves to a higher temperature with increasing Bi2Ti4O11 concentration 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 orientation as well as oxygen vacancy migration. Furthermore, E-field dependent resistive 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, the 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].