Abnormal piezoelectric and dielectric behavior of 0.92Na 0.5 Bi 0.5 TiO 3 -0.08BaTiO 3 induced by La doping
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Mankang Zhu, Yudong Hou, and Hui Yan Laboratory of Thin Film Materials, College of Beijing University of Materials of Science and Engineering, Beijing University of Technology, Beijing 100022, China
Riping Liu Key Laboratory of Metastable Materials of Science and Engineering, Yanshan University, Qinhuangdao 066004, China (Received 2 May 2006; accepted 18 September 2006)
Properties and phase structures of lead-free piezoelectric ceramics 0.92Na0.5Bi0.5TiO3-0.08BaTiO3 (NBT-BT) modified with La2O3 have been studied. Because of the different valence and ionic radius between La3+ and the exchangeable A-site ions, the lattice distortion and arrangement in the modified compounds can be expected, which will directly influence the phase composition and electrical characteristics of NBT-BT. Differing from familiar frame of gradual variability going with adulteration, NBT-BT doping 0.2–1.0 at.% La2O3 presents an abnormal increase of dielectric constant and a dramatic vanish of piezoelectricity. Further study on the relaxor property and domain structure implies that it originates from a typical relaxor-to-antiferroelectric crossover phase transition. However, a larger addition of La2O3 could rejuvenate the ferroelectricity and piezoelectricity of NBT-BT, correlating well with the model of competing ferro- and antiferroelectric interactions and metastable intermediate phase behavior in the morphotropic phase boundary region of complex perovskites. I. INTRODUCTION
Relaxor behavior in ferroelectric material resulting from compositionally induced disorder or frustration has been studied most extensively in disordered ABO3 perovskites.1 Sodium bismuth titanium, Na0.5Bi0.5TiO3 (NBT), is such a typical example because its A-site is occupied by two different cations, Na+ and Bi3+, with the ratio of 1:1. Regarding the advantages on nontoxicity and technologically excellent piezoelectric properties, NBT has been attached much importance and potentially expelled lead from commercial electric applications, especially transducer, sensors, and actuators, etc.2 To optimize its electrical properties, NBT is usually modified in two ways: first, NBT-based solid solutions are formulated with BaTiO3,2,3 SrTiO3,2,4 NaNbO3,5 K0.5Bi0.5TiO3,6,7 etc. Among them, the (1-x)NBT– xBaTiO3 system is fairly noticeable because of the existence of the morphotropic phase boundary (MPB). At room temperature, NBT and BaTiO3 possess rhombohedral and tetragonal symmetries, respectively. The soa)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0173 1188 J. Mater. Res., Vol. 22, No. 5, May 2007 http://journals.cambridge.org Downloaded: 07 Mar 2015
called MPB in (1-x)NBT–xBaTiO3 at the composition of x range from 0.06–0.08 is associated with a number of remarkable dielectric and piezoelectric properties.8 With regard to the phase composition and stability at the MPB, there are still some open questions. Recently, the lowsymmetry intermediate phase near MPB compositions was observed and reviewed in several piezoelectri
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