Lead-based perovskite-type solid solutions consisting of the ferroelectric and relaxor materials have attracted a growing fundamental and practical interest because of their excellent dielectric, piezoelectric and electrostrictive properties which are useful in actuating and sensing applications [1,2]. However, the sintering of PZT at high temperatures gives rise to a lead loss, which drastically degrades the device performance. Generally, a lead loss at high temperatures can be prevented by atmospherecontrolled sintering of PZT. However, such composition requires sintering at a high temperature (>1250˚C) in a controlled atmosphere to contain lead volatilization so as to avoid a shift in composition. To get around the problem, different sintering aids have been tried by various workers [3-5]. However, for practical applications, such sintering aids need proper selection so that the electrical and piezoelectric properties of the ceramics do not degrade.
The dielectric constants increased with the addition of NiO, Fe2O3, Gd2O3, Nb2O5 or WO3 and decreased with Cr2O3 or MnO2 addition [6-12]. Duran et al. studied the effect of MnO addition on the sintering and piezoelectric properties of Sm-modified lead titanate ceramics. The maximum density observed was 96.8% of the theoretical densit for 1% MnO addition at a sintering temperature of 1150˚C [
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)0.02]O3 and of structure perovskite.
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)0.02}1–zPz]O3 with z varying as 0, 2, 4, 6, 8, 10 and 12 wt% respectively. The samples were prepared by a conventional oxide mixing technique. The appropriate amounts of PbO (99.9%), TiO2 (99.9%), ZrO2 (99.0%), Ta2O5 (99.9%), CaO (99.9%), Cr2O3 (99.9%) and P2O5 (99.9%) powders were weighed and mixed by ball milling with partially stabilized zirconia balls as media in isopropyl alcohol for 6 h. After drying, the mixture was calcined in a covered alumina crucible at 800˚C for 4 h. The calcined powders were again ball milled for 24 h. The resulting powders were uniaxially compacted into pellets of 10 mm in diameter at a pressure of 5 MPa, followed by isostatically pressing at 150 MPa. To investigate their sintering behavior, the specimens were sintered in a sealed alumina crucible at temperatures ranging from 1000˚C to 1180˚C for 2 h. To limit PbO loss from the pellets, a PbO-rich atmosphere was maintained by placing an equimolar mix ture of PbO and ZrO2 inside the crucible. The weight loss of a well-sintered specimen was less than 0.5 wt%, thus a 0.5 wt% excess PbO was added to compensate for the lead loss during sintering. The bulk density was measured using the Archimedean method. The sintered compounds are carefully ground, then analyzed by the scanning electron microscopy (SEM) is a technical for estimating the size distribution, the average size of grains after sintering and qualitatively assess the presence of porosity. The micrographics are made using a Microscope JMS 6400. To investigate the electrical properties, the sintered disks were lapped on their major faces, and then sliver electrodes were deposited with a low temperature paste at 700˚C for 30 min. The piezoelectric samples were poled in a silicone oil bath at 100˚C by applying 20 kV/cm for 20 min. then cooling them under the same electric field. They were aged for 24 h prior to testing. The temperature dependence of dielectric properties was measured at temperatures ranging from room temperature to 420˚C with a heating rate of 2 ˚C/min using an impedance analyzer—HP4192A, Hewlett-Packard, Palo Alto, CA. The electromechanical coupling factor, kp, was determined by the resonance and antiresonance technique using another impendence analyzer (SI1260 Impedance/Gain-Phase Analyzer, Solartron, UK). (kp = [2.51(fa – fr)/fr)]1/2, where fr and fa are the resonance and anti-resonance frequencies, respectively [