Dielectric and electric properties of donor- and acceptor-doped ferroelectric SrBi2Ta2O9

Substitutions by aliovalent cations on the Sr2+ and Bi3+ sites of ferroelec tric SrBi2Ta2O9 (SBT) have been carried out, which result in modified diele ctric and electrical properties of SBT. The substitution of 10 mole % Fe3for Sr2+ shows an increase of 80 degreesC in T-C, whereas Ca2+ substitution for Bi3+ gives rise to diffused and frequency dispersive dielectric maxima with a relaxor-like behavior. The presence of Ca2+ in the (Bi2O2)(2+) laye rs appears to enhance the mobility of charge carriers thus increasing the b ulk conduction of the sample. On the other hand, Fe3+ addition in the perov skite-like units results in a sharp dielectric anomaly at the ferroelectric phase transition, with a bulk conductance similar to that of pure SBT comp ound, but with a reduced space charge relaxation time. The low temperature conductivity mechanism shows a frequency dependence, which can be ascribed to the space charge mainly due to the oxygen vacancies. The dielectric and conductivity properties of the Ca2+-doped SBT make it a promising material for the fatigue resistance in device applications. (C) 2001 American Instit ute of Physics.