Study of Dielectric and Piezoelectric Properties in the Ternary System Pb_0.98Ca_0.02[{(Zr_0.52Ti_0.48)_0.98(Cr³⁺_0.5 , Ta⁵⁺_0.5)_0.02}_1–zP_z]O₃ Doping Effects

Hamzioui Louanes, Kahoul Fares, Abdessalem Nora, Boutarfaia Ahmed

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DOI: 10.4236/msa.2012.31007                

Abstract

The effects of P₂O5 oxide on microstructure, dielectric and piezoelectric properties of Pb_0.98Ca_0.02[{(Zr_0.52Ti_0.48)_0.98( Cr³⁺_1/2,Ta⁵⁺_1/2)_0.02}_1–zP_z]O₃ ternary ceramics were investigated. Specimens with various contents of P₂O₅ from 0 to 12 wt. % were prepared by a conventional oxide mixing technique. The effect of P₂O₅ doping with regard to the development of the crystalline phase, density, microstructure, dielectric, ferroelectric and piezoelectric characteristics has been investigated. It has been found that the sintering temperature of piezoelectric Pb_0.98Ca_0.02[{(Zr_0.52Ti_0.48)_0.98(Cr³⁺_1/2,Ta⁵⁺_1/2)_0.02}_1–zP_z]O₃ can be reduced by phosphorus addition without compromising the dielectric properties. A sintered density of 94 % of the theoretical density was obtained for 4 wt. % P₂O₅ addition after sintering at 1050°C for 4 h. Ceramics sintered at 1050°C with 4 wt. % P₂O₅ achieve excellent properties, which are as follows: kp = 0.73, ρ = 0.09 × 10⁺⁴ (Ω. cm), εr = 18800, tanδ = 0.0094 and Tc = 390°C.

Keywords

PZT; Piezoelectricity; Electronic Materials; Dielectric Properties; Methods Physico-Chemical of Analysis

1. Introduction

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 [13]. The main role of dopants is generally improved physical and mechanical properties of these materials. This work aims at, to study the influence of P₂O₅ on the properties dielectric and piezoelectric of a ceramics material of general formula: Pb_0.98Ca_0.02[(Zr_0.52Ti_0.48)_0.98 (,)_0.02]O₃ and of structure perovskite.

2. Experimental Procedure

The compositions used for the present study were Pb_0.98 Ca_0.02[{(Zr_0.52Ti_0.48)_0.98(,)_0.02}_1–zP_z]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 [14]. Variation of the dielectric constant ε_r, resistivity and also the angle of the losses were examined by using a measuring bridge type RLC (bridge Schering) depending on temperature, concentration, the frequency.

3. Results and Discussion

3.1. Sintered Density

Figure 1(a) shows the variation of density with sintering temperature and the amount of P₂O₅ addition. This curves show the similar variation trend with increasing sintering temperature. The density of specimens sintered at 1050˚C showed the maximum value of 7.52 g·cm⁻³ at 4 wt% P₂O₅ and then was decreased after the maximum value. This variation is mainly attributed to the formation of liquid phase of excess PbO that improves densification of

Conflicts of Interest

The authors declare no conflicts of interest.

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