Aging-induced double hysteresis loops in bismuth-doped (Ba,Ca)TiO 3 ferroelectric ceramics
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Wang and Jing Shi Department of Materials Physics, School of Science, Xi’an Jiaotong University, Xi’an 710049, China
Delong Xu Institute of Powder Engineering, School of Material Science and Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China (Received 30 March 2009; accepted 21 May 2009)
Bismuth-doped (Ba1 xCax)TiO3 ceramics (x = 0.10, Bi-BCT) were prepared by a conventional solid-state reaction technique. An abnormal double-like hysteresis polarization–electric (P–E) loop was observed at room temperature for aged Bi-BCT. Raman scattering gives critical evidence for the formation of O2 vacancies in Bi-BCT. The change from the single P–E loops in the fresh samples to the double loops in the aged samples excludes the existence of a ferroelectric–antiferroelectric transition in Bi-BCT. A reversible domain switching mechanism resulting from a symmetry-conforming shortrange ordering of point defects gives a reasonable explanation for the naturally ageinduced double-like P–E loops in Bi-BCT. I. INTRODUCTION
Most ferroelectric (FE) materials exhibit aging effects (a gradual change in physical properties with time) in the FE state.1 This effect is normally found in acceptor-doped ferroelectrics, but not donor-doped ones. One important macroscopic effect, a double hysteresis loop in the polarization–electric field (P–E) relationship for aged samples, is expected to accompany the aging process. Interestingly, double hysteresis (P–E) loops have been observed in Pbbased,2–5 (Na,Bi)TiO3-based,6–8 BaTiO3/(Ba,Sr)TiO3,9,10 KNbO3,11 and BiFeO312 ceramics. However, in perovskite ABO3 ferroelectric materials,2–12 the observed double P–E loops have different origins. Generally speaking, these double P–E loops result from antiferroelectric components, an electric field induced paraelectric–ferroelectric (PE–FE) phase transition near the Curie temperature (Tc), or an aging effect far below Tc. However, until now, there has been no direct indication of the appearance of antiferroelectric components in (Ba,Ca)TiO3.13–18 Besides, the double P–E loops observed in (Na,Bi)TiO3-based ceramics6–8 are at temperatures near Tc, while those reported in aged BaTiO3/(Ba,Sr)TiO3,9,10 KNbO3,11 and BiFeO312 are far below Tc. These give essential evidence that aging may induce double P–E loops in (Ba,Ca)TiO3 at room a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0375 J. Mater. Res., Vol. 24, No. 10, Oct 2009
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temperature. Although studies have been devoted to the structural and dielectric characteristics of (Ba,Ca)TiO3 ceramics,13–18 few reports has been made on the ageinduced double ferroelectric hysteresis effect for (Ba,Ca) TiO3 ceramics. In this paper, we explain the double P–E loops observed in bismuth doped (Ba,Ca)TiO3 ceramics based on a symmetry-conforming short-range ordering (SC-SRO) mechanism of point defects, as proposed by Ren and co-workers.9–11 II. EXPERIMENTAL
A conventional solid reaction route
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