Elsevier

Ceramics International

Volume 37, Issue 7, September 2011, Pages 2135-2142
Ceramics International

Fabrication and characterization of (Pb(Mg1/3Nb2/3)O3, Pb(Yb1/2Nb1/2)O3, PbTiO3) ternary system ceramics

https://doi.org/10.1016/j.ceramint.2011.03.059Get rights and content

Abstract

New ternary compositions in the Pb(Mg1/3Nb2/3)O3-Pb(Yb1/2Nb1/2)O3–PbTiO3 (PMN-PYbN-PT) system were prepared using 0.5Pb(Yb1/2Nb1/2)O3-0.5PbTiO3 (PYbNT) and (1-x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (x = 0.26; PMNT26 or x = 0.325; PMNT32.5) powders synthesized via the columbite method. Dense (≥ 96% of theoretical density) ceramics with PMN/PYbN mole ratios of 25/75 (R-25), 50/50 (R-50) and 75/25 (R-75T and R-75R) were fabricated by reactive sintering at 1000 °C for 4 h. Therefore, incorporation of PYbNT to PMNT successfully decreased sintering temperature of PMNT from 1200 °C-1250 °C to 1000 °C. Samples with higher density and perovskite ratio together with lower weight loss possessed higher dielectric and piezoelectric values in each composition. The R-75 samples had remanent polarization (Pr) values of 34-36 μC/cm2 and piezoelectric charge coefficient (d33) of 560 pC/N. The sharp phase transition PMNT as a function of temperature became broader or more diffuse with increasing PYbNT content. However, PYbNT addition to PMNT increased Curie temperature (Tc) from 183 °C (for PMNT32.5) to 220-242 °C (for R-75T and R-75R) to 336 °C (for R-25). Therefore, these ternary compositions can be tailored for various high temperature applications due to the relatively higher Tc with enhanced piezoelectric and dielectric properties as compared to PMNT.

Introduction

Lead-based relaxor ceramics with a general formula Pb(B1B2)O3 have excellent dielectric and piezoelectric properties [1], [2], [3], [4], [5]. Relaxor Pb(Mg1/3Nb2/3)O3 (PMN) ferroelectric (FE) possesses good voltage stability, superior electrostrictive effects, low sintering temperature and a dielectric response. However, its Curie temperature (Tc) is approximately −15 °C, which restricts many device applications [6], [7], [8], [9], [10]. The Tc of PMN can be increased by adding a normal FE PbTiO3 (PT) with a higher Tc (∼490 °C) [6], [7]. The Tc is shifted to higher temperatures due to the formation of a solid solution between PT and PMN. (1-x)PMN-xPT system, which displays good piezoelectric and pyroelectric properties near a morphotropic phase boundary (MPB) (between 0.3 and 0.35 mol% PT) [8]. Accordingly, dielectric and electromechanical properties are also changed due to the formation of a MPB [8], [11].

Conventional and reactive sintering methods have been applied to densify PMN-PT ceramics [12], [13]. Reactive sintering is a process in which phase formation and densification are both achieved in the same heat treatment. However, the two steps can occur concurrently or in sequence, depending on processing and starting materials [14]. 0.68PMN–0.32PT ceramics with 4 wt% excess PbO were reactively sintered at 1250 °C via the columbite method [15]. These ceramics had a remnant polarization (Pr) ∼21 μC/cm2, a coercive field (Ec) ∼8.8 kV/cm, Tc ∼190 °C, and a piezoelectric charge coefficient (d33) ∼325 pC/N [15]. The d33 was found to be 590 pC/N for the same composition that consisted of 0.5 wt% excess PbO [16]. Whereas, 0.68PMN–0.32PT ceramics fabricated at 1230 °C via one-step calcination without excess PbO possess Pr ∼26.2 μC/cm2, Ec ∼4.1 kV/cm, Tc ∼138 °C, and d33∼458 pC/N [17].

The dielectric and piezoelectric properties are enhanced near the MPB compositions because of large number of polarization directions available. High dielectric and piezoelectric properties associated with low Tc come at the expense of more temperature-dependent properties and low depoling temperatures. Thus, ceramic compositions near MPB with high Tc are desired [18]. Although PMN–PT ceramics have good FE properties, their Tc's are quite low which restricts the working range of the devices based on these materials. Our recent work showed that the addition of a high Tc ceramic (e.g., 0.5Pb(Yb1/2Nb1/2)O3-0.5PbTiO3, hereafter referred to as PYbNT) increased the Tc of the PMN-PT composition without degrading the electrical properties [19]. (1-x)PYbN-xPT solid solution has a MPB composition at x = 0.5 with a Tc ∼360 °C [18], [20]. In addition, PYbNT ceramics reactively sintered at temperatures as low as 950 °C using 3 wt% excess PbO were reported to have enhanced dielectric and piezoelectric properties such as Pr ∼36 μC/cm2, Ec ∼ 22 kV/cm and d33 ∼508 pC/N together with a high Tc∼ 371 °C [20].

The objective of this study is to formulate ceramic compositions in ternary PMN–PYbN–PT system to achieve enhanced dielectric and piezoelectric properties. PMN/PYbN mole ratio at 25/75, 50/50 and 75/25 will be primarily discussed based on our previous 50/50 mole ratio study [19]. With the addition of PYbNT to PMNT, the Tc of the latter can be increased and the sintering temperature of the ternary system can be decreased. Ultimately, the objective is to produce ternary compositions with enhanced properties and to provide temperature stability for higher temperature device applications. Densification, phase formation as a function of sintering temperature between 950 °C and 1200 °C and dielectric and piezoelectric properties are also reported.

Section snippets

Experimental Procedure

(MgCO3)4.Mg(OH)2.5H2O (Sigma-Aldrich Chemie GmbH, Germany), Nb2O5 (Alfa Aesar GmbH & Co. KG, Germany), (PbCO3)2.Pb(OH)2 (Alfa Aesar), TiO2 (Evonik Degussa Industries AG, Germany) and Yb2O3 (Alfa Aesar) were used as starting materials. The steps involved in the synthesis of powders and final compositions are summarized in Table 1. All powders were mixed in a Nalgene™ (Nalgene Labware, Denmark) bottle by ball milling using ZrO2 media in isopropyl alcohol and then dried on a hot plate at 50 °C with

Phase formation and densification

XRD patterns in Fig. 1 show the phase evolution of the R-75T samples as a function of sintering temperature between 950 °C and 1200 °C for 4 h. Single perovskite phase was maintained up to 1200 °C; however, a non-perovskite pyrochlore phase (marked as *) was observed in ceramics sintered at 1200 °C for 4 h. The reflections from tetragonal phase (as shown in inset in Fig. 1) are clearly seen from splitting in {200} peaks near 2θ∼45°.

Fig. 2 compares the XRD patterns of the PMN-PYbN-PT based ceramics

Conclusions

New ternary compositions in the Pb(Mg1/3Nb2/3)O3-Pb(Yb1/2Nb1/2)O3–PbTiO3 (PMN-PYbN-PT) system were prepared using 0.5Pb(Yb1/2Nb1/2)O3-0.5PbTiO3 (PYbNT) and (1-x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (x = 0.26; PMNT26 or x = 0.325; PMNT32.5) powders synthesized via the columbite method. Dense (≥ 96% of theoretical density) ceramics with PMN/PYbN mole ratios of 25/75 (R-25), 50/50 (R-50) and 75/25 (R-75T and R-75R) were fabricated by reactive sintering at around 1000 °C for 4 h. Therefore, incorporation of PYbNT to

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