Influence of porosity on the dielectric response and central-mode dynamics in PbZrO3 ceramics

Dielectric response of two types of nominally pure hot-pressed PbZrO3 ceramics (PZ1 and PZ2) of similar density (97-98%) was studied in the 1 MHz-1 GHz and far infrared frequency ranges in a wide temperature interval. While the far infrared spectra of both ceramics did not significantly differ from that of the crystal and the permittivity of PZ1 appeared to be comparable to that of the crystal, the permittivity of PZ2 was much lower. This reduction was particularly drastic (of about four times) on approaching the antiferroelectric phase transition from the paraelectric phase. We succeeded to explain this effect using a brick-wall model assuming nano-cracks development along some of the grain boundaries in PZ2 in agreement with SEM observations and unusual mechanic fragility of this ceramics. Our estimates show that even small volume fraction (<1%) of the air gaps in the sample may drastically reduce its low-frequency permittivity and cause pronounced stiffening of the central-mode-type dispersion in PbZrO3.