Defect-dipole alignment and strain memory effect in poled Li doped (Bi0.5Na0.4K0.1)0.98Ce0.02TiO3 ceramics

Abstract

Asymmetric ferroelectric hysteresis (P-E) loops and strain hysteresis (S-E) curves are detected in poled-aged Li doped (Bi 0.5 Na 0.4 K 0.1 ) 0.98 Ce 0.02 TiO 3 ceramics at room temperature. Temperature dependence of electrical and structural analysis is used to study the stability of electrically induced long-range ferroelectric order. Interestingly, this asymmetric characteristic can sustain at 80°C B T B 90°C, where the ferroelectric and non-ergodic relaxor phase coexist. Our results suggest that the preferentially reoriented defect dipoles have the pinning effect on temperature-and electric field-induced phase transition between long-range ferroelectric and relaxor.The aging effect is the time-dependent change of materials in ferroelectric, dielectric and piezoelectric characteristics [1,2]. A large recoverable electro-strain that stems from the reversible domain switching, accompanying with double polarization-electric field (P-E) hysteresis loop, has been observed in many aged acceptor perovskite ferroelectric materials. The mechanism can be attributed to the effect of the symmetry-conforming principle of point defects [3]. An internal bias field is present in the poling direction after aging in poled ferroelectrics, leading to strong asymmetric P-E loops and polarization-electric field strain (S-E) loops [4,5]. Continuous operating electric field is avoided for keeping a stable strain output in materials with strain memory effect [6], which is advantageous for some actuator applications.Bi 0.5 Na 0.5 TiO 3 (BNT) based material have attracted great attention after the recent discovery of the large strain [7][8][9][10][11], which is associated with the reversible phase transitions between relaxor and ferroelectric [12][13][14]. Recently, Fe-doped BNT-BaTiO 3 are reported to present aging effects in the poled state, but are absent in the relaxor state [15]. However, the effect of acceptor doping in BNT based material still need be further studied, due to the existence of relaxors phase with special polar structure at virgin state and the unique field-and temperature-induced phase transition in it. In this paper, strain memory effects are reported in Li 2 CO 3 doped (Bi 0.5 Na 0.4 K 0.1 ) 0.98 Ce 0.02 TiO 3 ceramics. The thermally stimulated depolarization currents (TSDC), temperature-dependent dielectric performance and X-ray diffraction (XRD) are measured to identify the influence of defect dipole on temperature-induced ferroelectric to relaxor phase transition. The asymmetric P-E and S-E loops at a broad temperature range are discussed to clarify the effect of defect dipole on fieldinduced relaxor to ferroelectric phase transition.The 0.5 mol % Li 2 CO 3 doped (Bi 0.5 Na 0.4 K 0.1 ) 0.98 Ce 0.02 TiO 3 (Li, Ce-BNKT) ceramics were prepared by a conventional solid state reaction technique sintered at 1150°C for 4 h. The P-E and S-E loops were measured at 1 Hz using a ferroelectric test unit (TF-2000, aix-ACCT, Aachen, Germany) for 30-120°C. During the polarization procedure, the samples were heated to a polari...

Improving the Functional Control of Aged Ferroelectrics Using Insights from Atomistic Modeling

“…Instances of large asymmetric S-E loops have been experimentally reported in a range of ferroelectric materials [38]. In [39], the authors report a strain difference of 0.15% in Li doped (Bi 0.5 Na 0.4 K 0.1 ) 0.98 Ce 0.2 TiO 3 ceramics which they propose is due to alignment of (Li…”

Defect Dipole Behaviors on the Strain Performances of Bismuth Sodium Titanate-Based Lead-Free Piezoceramics

“…Shi et al reported a defect dipole induced by partial Li + entering the B site in Li-substituted (Bi 0.5 Na 0.4 K 0.1 ) 0.98 Ce 0.02 TiO 3 (Li, Ce-BNKT) in which the (Li Ti − V •• O ) will create an asymmetric shift of the hysteresis loop and the strain curve in the polarized FE phase region that causes a large strain memory effect. When the temperature is higher than the depolarization temperature within a certain range, although it has entered the ER phase, the hysteresis loop and strain still retain asymmetry, as displayed in Figure 8, as a result of the directional pinning action of defect dipoles in the remaining ferroelectric phase [85].…”

Inorganic dielectric materials for energy storage applications: a review

“…For example, the technique of co-doping at the A and B site of perovskite structure of BNKT ceramics with dopants such as Ta [253], Nb [254], Zr [255], Hf [256], Mn [257], Li [258], and La [259], etc reported improved piezoelectric and energy storage applications [72,[260][261][262]. Details of co-doped ferroelectric BNT-systems are also reported elsewhere [72,[260][261][262][263][264][265][266][267]. Similarly, the co-doped system of 0.96[{Bi 0.5 (Na 0.84 K 0.16 )} 1−x−y Li x Mg y (Ti 1−z Nb z ) 3 ] -0.04SrTiO 3 reported enhanced energy storage performance in a temperature range of 100 • C-150 • C, with an energy storage density of 0.70 J cm −3 at an electric field of 5.5 kV mm −1 [260].…”