The effect of grain size on the high field dielectric properties of hard PZT ceramics

Hard (Mn-doped) PZT ceramics having grain sizes in the range 4 to 9 mu m we re subjected to an AC electric field with an amplitude E-0 of 0.1 to 3.5 kV mm(-1). The dielectric characteristics were determined by analysis of the measured P-E (polarisation-electric field) hysteresis data. It was found th at the saturation polarisation P-s, measured at a field amplitude of 3.5 kV mm(-1), reduced from 29 to 21 mu C cm(-2) as the grain size reduced from 7 .1 to 4.1 mu m, indicating an increased resistance to ferroelectric domain switching in the fine-grained material. In contrast, the dielectric permitt ivity and loss (epsilon(r)', epsilon(r)"), measured in the field range belo w the coercive field E-c, both increased with a reduction in grain size; th is was attributed to an increase in the domain wall density in fine-grained ceramics. Near-linear epsilon(r)'-E-0 plots were obtained for 0.3 kV mm(-1 ) < E-0 < 1.7 kV mm(-1), giving a good fit to the Rayleigh Law. Rayleigh co efficients of 0.81 x 10(-3) 0.64 x 10(-3) and 0.53 x 10(-3) m V-1 were obta ined for hard PZT ceramics having grain sizes of 4.1, 7.1 and 8.9 mu m resp ectively.