Effect of MnO2 Impurity on the PZT-PMN System Ceramics for Piezoelectric Transformer
The PZT-PMN ceramics system was derived from Pb(Zr0.5Ti0.5)O3 and Pb(Mg2/3Nb1/3)O3 based compositions those obtained via the columbite method. The effect of MnO2 addition on microstructure, physical properties and piezoelectric properties were investigated. In this study, the composition with PZT/PMN ratio of 1:1 was selected. To observe the effect of MnO2 adding, its concentration was varied in range 0-10 mol%. Green pellets were sintered at temperature 1250oC for 4 hours. For piezoelectric investigation, the ceramics pellets were subjected to a poling process. The XRD results show that there is no phase transformation observed for all sintered PZT-PMN samples with presence of MnO2. The SEM micrographs reveal that MnO2 can enhance sinterability as evidenced by lowering of porosity and increasing of grain size with increasing of MnO2 content. Increasing of linear shrinkage and apparent densities also confirmed such effect. Improvement of d33 from 28 to 114 pC/N could only found for MnO2 in range 0 to 4 mol%. For higher MnO2 content, there is only slightly increased. However, increasing of kp with increasing of MnO2 is clearly observed. While dielectric constant measured at room temperature and at frequency 1 kHz is higher for ceramics without MnO2 doping and it decreases with increasing MnO2 concentration. The temperature dependence of relative dielectric constant go to peak of value about 6000 at temperature around 180oC and shifting of these peaks with frequency can only be observed for samples with higher MnO2 content. This indicates a normal ferroelectric behavior for sample with lower MnO2 and there are converted to relaxor after MnO2 increased.
Y. Suwan et al., "Effect of MnO2 Impurity on the PZT-PMN System Ceramics for Piezoelectric Transformer", Advanced Materials Research, Vols. 55-57, pp. 189-192, 2008