Superior and anti-fatigue electro-strain in Bi_0.5Na_0.5TiO₃-based polycrystalline relaxor ferroelectrics

Abstract

By composition engineering and subtle criticality confinement, a giant recoverable electro-strain (S > 0.7%) with reduced hysteresis is reported in BNT-based relaxor ferroelectrics, which can be kept at a high level (<2% variation) even after 105 fatigue cycles.

Domain‐scale imaging to dispel the clouds over the thermal depolarization of Bi0.5Na0.5TiO3‐based relaxor ferroelectrics

“…When the operating temperature is higher than the T d region ( T = 85°C), a sizeable remnant strain S rem (0.087% at 85°C) can still be observed, indicating that the E ‐field‐induced transition from the initial relaxor state to the ferroelectric state (first cycle) is irreversible, although the following cycles provide the reversible evidence for the transition between the ferroelectric state and the residual relaxor state. Here, we can conclude that the giant and recoverable electro‐strain is actually originated from the reversible transition between the residual relaxor state and ferroelectric state . According to the results of domain profile ( T ≥ 100°C) provided in Figures A and A, the clear discrepancy of domain sizes can be observed between the initial and residual relaxor state, indicating that the residual broken domains (domain width: 0.28‐0.71 μm) exhibit a rather larger coherence length than that of the incipient labyrinth‐like topological domains (0.044‐0.334 μm).…”

“…Here, we can conclude that the giant and recoverable electro-strain is actually originated from the reversible transition between the residual relaxor state and ferroelectric state. 4,21 According to the results of domain profile (T ≥ 100°C) provided in Figures 2A and 3A, the clear discrepancy of domain sizes can be observed between the initial and residual relaxor state, indicating that the residual broken domains (domain width: 0.28-0.71 μm) exhibit a rather larger coherence length than that of the incipient labyrinth-like topological domains (0.044-0.334 μm).…”

“…For the poled BNKT sample, its temperature‐dependent XRD plots (Figure E‐H) present the clearer symmetry than the unpoled one, conforming well with the point that the residual broken domains exhibit a rather larger coherence length than the incipient domains. According to the refined structural parameters shown in Table , one can see that the ratio of P 4 bm gets an obvious increase (from 0.199 at 70°C to 0.466 at 85°C) when the temperature crosses the T d region, indicating that the structural transition from long‐range‐correlated R 3 c ( a − a − a − anti‐phase tilting) to short‐range‐correlated P 4 bm ( a 0 a 0 c + in‐phase tilting) should be the driving force for the fluctuations of poling‐induced large‐sized‐oriented domains . With the further increase of temperature, the short‐ranged P 4 bm ( a 0 a 0 c + in‐phase tilting) gradually becomes predominant (Figure H and Table ), leading to the low‐hysteresis P ‐ E loops (Figure D) and the decreased tan δ (Figure F) at 150°C …”

“…According to the refined structural parameters shown in Table 1, one can see that the ratio of P4bm gets an obvious increase (from 0.199 at 70°C to 0.466 at 85°C) when the temperature crosses the T d region, indicating that the structural transition from long-range-correlated R3c (a − a − a − anti-phase tilting) to short-range-correlated P4bm (a 0 a 0 c + in-phase tilting) should be the driving force for the fluctuations of poling-induced large-sized-oriented domains. [21][22][23] With the further increase of temperature, the short-ranged P4bm (a 0 a 0 c + in-phase tilting) gradually becomes predominant ( Figure 5H and Table 1), leading to the low-hysteresis Figure 5D) and the decreased tan δ ( Figure 1F) at 150°C. [21][22][23] We finally give the conceptual domain-scale model extracted from the aforementioned results conclusively, as provided in Figure 6.…”

Second‐order‐transition like characteristic contributes to strain temperature stability in (K, Na)NbO3‐based materials

“…8,12,18,[26][27][28][29] However, for displacement-actuator applications, comparable normalized strain (d 33 *, strain normalized by a given electric field) is another hot topic in the field of lead-free materials. 26,[30][31][32] Nevertheless, a high d 33 * and good temperature stability for KNN-based ceramics is a contradiction because the phase transition in such materials is sensitive to the surrounding temperature, in which phase compositions deviate and performance declines with the variation in temperatures. 29,33 Previously, some efforts were made to improve the temperature stability of KNN-based ceramics, including shifting T O-T below room temperature, creating overlapped phase transitions over a broad temperature range (or successive phase transitions), and constructing rhombohedral-tetragonal (R-T) coexistence near room temperature.…”