In situ neutron powder diffraction patterns and dielectric spectra of 0.93Bi0.5Na0.5TiO3-0.07BaTiO3 ceramic were investigated under different electrical fields and temperatures. An electric-field-induced phase transition from metrically cubic to metrically tetragonal, associated with strong domain wall motion, occurs. Such induced phase and domain wall motion are unchanged until the high-temperature phase transition occurs from metrically tetragonal to metrically cubic. All these changes are irrelevant to the observed depolarization temperature (75°C). The depolarization behaviour is thus suggested to be associated with the local structure caused by the octahedral tilt twinning disorder. 1. Introduction Piezoelectric materials are used in a variety of devices such as stress sensors, ultrasound emitters, and large-strain actuators. The ultrahigh strain (~1.7%) in oriented rhombohedral Pb(Zn1/3Nb2/3)O3-PbTiO3 and Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals is suggested to be a result of the electric-field-induced rhombohedral-tetragonal phase transition [1–4]. Lead-free BiFeO3 films have a reversible electric-field-induced strain of over 5% that arises from moving the boundaries between tetragonal- and rhombohedral-like phases [5]. In fact, such electric-field-induced structural transition is found to be universal in rare-earth-substituted BiFeO3 [6], resulting from isostructural transitions, disappearance and reappearance of the tilting of the oxygen octahedral, and reentrance into specific crystallographic classes [7]. This phenomenon also occurs in other lead-free piezoelectric material systems [8, 9]. ( )Bi0.5Na0.5TiO3- BaTiO3 (BNTBT) ceramic has been intensively studied as a candidate for lead-free piezoelectric materials due to the high strain that appeared in the morphotropic phase boundary compositions ( ) [10]. Such high strain is suggested to be related to the electric-field-induced structural changes [11–13]. It is found that BNTBT undergo a ferroelectric to antiferroelectric transition above a so-called depolarization temperature ( ) above which the piezoelectric properties deteriorate [14]. In this paper, we aim to investigate the variation in the structure and domain texture of 0.93Bi0.5Na0.5TiO3-0.07BaTiO3 ( , abbreviated as BNTBT7 hereafter) ceramic under the electrical field and with increasing temperature via in situ neutron diffraction technique in order to understand the relationship between the structural change under the applied electric field and the depolarisation behaviour at elevated temperature. 2. Experimental BNTBT7 ceramic was
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