Effects of average and local structure on the dielectric behavior of (1−x)BaTiO[sub 3]–xLaYO[sub 3] (0≤x≤0.40) ceramics

The dielectric properties of dense ceramics of (1−x)BaTiO3–xLaYO3 (LBTY) (0 ≤ x ≤ 0.40) were characterized in the temperature range 10 to 450 K. The Curie temperature, Tc, of LBTY ceramics decreases at a rate of −23 K/at. % (La,Y) for x<0.10 but increases at +7 K/at. % (La,Y) for x ≥ 0.20. The room temperature relative permittivity, εRT, decreases from ∼ 2000 for x = 0.10 to ∼ 57 for x = 0.40. This variation is accompanied by a substantial reduction in the temperature dependence of the relative permittivity, εr, and also by the emergence of relaxor ferroelectric-like behavior at x>0.05. The gradual transition from a classical ferroelectric to a relaxor-type response results from disruption of the long-range ferroelectric order, believed to be caused by a nanoclustering phenomenon. x = 0.10 exhibits all the characteristic features of a relaxor-ferroelectric, i.e., εr decreases and tan δ increases with increasing frequency. For x>0.20 the relaxor behavior becomes progressively more subtle, suggesting a weaker coupling between the polar nanoregions. The poor microwave dielectric properties of LBTY ceramics, in particular for x = 0.40, which exhibit εRT ∼ 57 and a quality factor of ∼ 755 GHz are attributed to phase separation on the nanometer scale.