Electrical properties of Na1/2Bi1/2TiO3–BaTiO3 ceramics
Introduction
Ever since the discovery of piezoelectric effect, piezoelectric materials have been rapidly developed and widely used. At present, the most widely-used piezoelectric materials are Pb(Zr,Ti)O3(PZT)-based ceramics because of their superior piezoelectric properties. However, because the evaporation of harmful lead oxides during the preparation of Pb-contained ceramics has detrimental influence on environment, lead-free piezoelectric materials such as Na1/2Bi1/2TiO3-based oxides, bismuth layer structure oxides and tungsten bronze-type oxides have been studied in order to replace PZT-based ceramics.
Sodium bismuth titanate, Na1/2Bi1/2TiO3, is a kind of perovskite ferroelectric discovered by Smolenskii et al. in 1960.1 At room temperature, Na1/2Bi1/2TiO3 is strongly ferroelectric with a relatively large remnant polarization, Pr=38 μC/cm2, and a relatively large coercive field, Ec=73 kV/cm.1 Because of its large coercive field and relatively large conductivity, pure Na1/2Bi1/2TiO3 is hard to be poled and its piezoelectric properties is not desirable. Therefore Na1/2Bi1/2TiO3-based solid solutions were studied to improve piezoelectric properties. Na1/2Bi1/2TiO3-based ceramics are considered to be one group of promising lead-free or low-lead piezoelectric ceramics.2, 3, 4, 5, 6, 7, 8 Na1/2Bi1/2TiO3–BaTiO3 ceramics were studied by several researchers.2, 7 The morphotropic phase boundary (MPB) of this solid solution system is near x=0.06. Takenaka reported that the composition of (Na1/2Bi1/2)0.94Ba0.06TiO3, which is near the MPB, has relatively good piezoelectric properties. The coupling factor and piezoelectric constant of the composition are k33=0.55, k31=0.19, d33=125 pC/N and d31=40 pC/N, respectively.2
In this paper, the piezoelectric properties of Na1/2Bi1/2-TiO3–BaTiO3 ceramics near the morphotropic phase boundary (MPB) were studied. Influences of nonstoichiometry and doping on piezoelectric properties and structure of (Na1/2Bi1/2)0.92Ba0.08TiO3 ceramics were further studied.
Section snippets
Experimental procedures
The conventional mixed oxides method was used to prepare Na1/2Bi1/2TiO3–BaTiO3 ceramics according to formulas of (1−x) Na1/2Bi1/2TiO3–xBaTiO3 (x=0.02, 0.04, 0.06, 0.08, 0.10) (abbreviated as NBBTX, X=2, 4, 6, 8, 10), (Na1/2Bi1/2)0.92−xBa0.08TiO3 (abbreviated as NBBT81), (Na1/2Bi1/2)0.92+xBa0.08TiO3 (abbreviated as NBBT82), (Na1/2Bi1/2)0.92Ba0.08TiO3+xNb2O5 (abbreviated as NBBT83) and (Na1/2Bi1/2)0.92Ba0.08 TiO3+xCo2O3 (abbreviated as NBBT84) (x⩽0.01). The starting raw materials were
The X-ray diffraction patterns of (1−x) Na1/2Bi1/2TiO3–xBaTiO3 ceramics
The X-ray diffraction patterns of (1−x) Na1/2Bi1/2-TiO3–xBaTiO3 (x=0.02, 0.04, 0.06, 0.08, 0.10) ceramics are shown in Fig. 2. The NBBTX ceramics were all pure perovskite structure. At room temperature, the symmetry of Na1/2Bi1/2TiO3 is rhombohedral and BaTiO3 is tetragonal. Their solid solutions have rhombohedral-tetragonal morphotropic phase boundary (MPB). X-ray diffraction revealed that NBBT2 and NBBT4 ceramics were rhombohedral symmetry. With the increasing component of BaTiO3, the
Conclusion
Piezoelectric properties of Na1/2Bi1/2TiO3–BaTiO3 ceramics system with perovskite structures were studies. The main electrical properties of (1−x)Na1/2Bi1/2TiO3–xBaTiO3 ceramics reach extreme values near the MPB. Na1/2Bi1/2TiO3–BaTiO3 ceramics possess the properties of large ratios of kt/kp, low dielectric constant and high frequency content, which are suitable for ultrasonic applications. Influences of nonstoichiometry and doping on the structure and piezoelectric properties of (Na1/2Bi1/2)0.92
Acknowledgements
We would like to thank Professors Wang Pingchu and Pan Xiaomin for their help in experiment. The work was funded by the National High Technology Research and Development Program of China (863 Program No. 2001AA325070).
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