Effect of Phase Transitions on Thermal Depoling in Lead-Free 0.94(Bi_0.5Na_0.5TiO₃)–0.06(BaTiO₃) Based Piezoelectrics

Abstract

0.94­(Bi0.5Na0.5TiO3)–0.06­(BaTiO3) (BNTBT) is a potential lead-free piezoelectric candidate to replace lead-based PZT ceramics. The thermal depoling temperature sets the upper limit for the high temperature application of piezoelectric materials. Recently, an interface model was proposed to explain the good resistance to thermal depoling of BNTBT-ZnO composite. However, we found that the presence of ZnO was not limited to the interface, but contributed intrinsically to the BNTBT lattice. This played a critical role in the structural changes of BNTBT, confirmed by a unit volume change supported by XRD, which was further proved by Raman, EDS, and dielectric characterization at different temperatures. The previous interface model is not correct because BNTBT shows thermally stable piezoelectric properties, even though there is no interface between BNTBT and ZnO. The thermal depoling behavior of BNTBT-based materials is directly related to the transition temperature from the rhombohedral phase to the tetragonal phase in our phase transition model, which is consistent with four current peaks in their ferroelectric loops close to the depoling temperature.

Enhanced pyroelectric properties in (Bi0.5Na0.5)TiO3–BiAlO3–NaNbO3 ternary system lead‐free ceramics

“…The variation of (111) diffraction peaks indicate that the addition of NN tends to decrease the fraction of rhombohedral phase in BNT–BA ceramics. As well known, the rhombohedral R3c structure is polar, with parallel displacement of A‐ and B‐site cations along (111) direction . Therefore, it can be inferred that increasing the NN content will result in the disruption of the long‐range polar phase.…”

“…It can be observed that all the ε r − T curves show weak frequency dispersion well below T FR , which is related to the electric‐field induced long‐rang ferroelectric (FE) order . As the temperature increases to T FR , the induced FE order can be transformed into nanodomains or PNRs as evidenced by the stronger frequency dispersion of dielectric constant . With further heating at T m , the ergodic phase is changed into paraelectric phase .…”

“…Please note that the T d of x = 0 was outside the measurement temperature range, so the peak was not detected. In BNT‐based ceramics, T d was ascribed to ferroelectric to relaxor phase transition, where the majority of the oriented dipoles are disrupted . Therefore, a significant pyroelectric current is released at T d as shown in Figure A.…”

“…The great enhancement of p was always realized at the expense of lowering the T d to near room temperature (RT). In BNT‐based materials, T d was recognized as corresponding to ferroelectric to relaxor phase transition . Generally, the presence of phase transition in the working temperature window will produce undesirable non‐linear pyroelectric responses.…”

Role of oxygen‐vacancy in piezoelectric properties and fatigue behavior of (Bi0.5Na0.5)0.93Ba0.07Ti1+xO3 ceramics

“…When the maximum negative field was applied, the weakly polar phase changed again to a polar phase that corresponded to the peak at − E F . Similarly, upon reversing the applied field, the polar phase transformed back again to a weakly polar phase that corresponded to the peak at − E B . The other compositions that contained either a Ti deficiency or excess Ti exhibited saturated P ‐ E loops with two typical domain switching current peaks at the coercive field ± E c .…”