Ageing of high field dielectric properties in -based piezoceramics

Abstract

The dielectric ageing characteristics of a commercial cobalt-doped ceramic have been determined over a range of applied field strengths (field amplitude from 0.1 to 2.0 kV ) and temperatures (30, 60, ). P-E (polarization-electric field) hysteresis data were obtained, from which the internal bias field , polarization amplitude and the effective high field dielectric coefficients and were determined. Near-saturated P-E loops were obtained at high field levels (); it was shown that increased gradually during ageing to yield an ultimate value around 0.6 kV after ageing for 17 h at . The ultimate value was reduced to approximately 0.4 kV at a higher ageing temperature of . The P-E `sub-loops' obtained for showed a pronounced asymmetry and high loss at early ageing times, which were attributed to a combination of partial ferroelectric domain switching and domain wall vibration. These characteristics were effectively removed by domain stabilization during ageing, giving rise to a near-linear P-E relationship with apparently zero internal bias field at long ageing times. The effective dielectric coefficients , and derived from these P-E data all reduced significantly during ageing, giving an almost loss-free dielectric response after ageing for 17 h. The dielectric behaviour at early ageing times was attributed to a combination of the intrinsic (ionic) response, ferroelectric domain wall vibration and partial domain switching. The two lossy domain-related polarization mechanisms were effectively `frozen out' by domain stabilization processes during ageing, which enabled a quantitative determination of the three contributions to the complex permittivity at various ageing times, field amplitudes and temperatures.