Dielectric relaxation in Ba-based layered perovskites

Ferroelectric materials with Bi-layered structure such as SrBi2Ta2O9 and Sr Bi2Nb2O9 are now intensively investigated in view of their applications in nonvolatile computer memories and high-temperature piezoelectric transducer s. When Sr2+ is substituted with Ba2+, a significant disorder is induced an d the material exhibits broadening of the phase transition. Such broadening is essential for applications since it allows achieving smooth temperature characteristics while maintaining high dielectric and piezoelectric proper ties. In this work, stoichiometric dense BaBi2Nb2O9 (BBN) ceramics are sint ered using a mixed oxide route. Dielectric and ferroelectric properties are investigated in a broad range of temperatures and frequencies. Strong disp ersion of the complex relative dielectric permittivity is observed includin g typical relaxor features such as shift of the permittivity maximum with f requency and broadening of the relaxation time spectrum with decreasing tem perature. The dielectric relaxation obeys the Vogel-Fulcher relationship wi th anomalously low freezing temperature (T(f)approximate to 100 K), which i s much lower than the permittivity maximum in the radio-frequency range. Po larization hysteresis loops testify linear properties of BBN at all tempera tures above T-f. The properties of BBN ceramics are compared to conventiona l relaxor systems such as Pb(Mg, Nb)O-3 and (Pb, La)(Zr, Ti)O-3. (C) 2001 A merican Institute of Physics.