Optimized strain performance in <001>-textured Bi0.5Na0.5TiO3-based ceramics with ergodic relaxor state and core—shell microstructure

Abstract

Herein, a high strain of ∼0.3% with a small hysteresis of 43% is achieved at a low electric field of 4 kV/mm in the highly &lt;001&gt;-textured 0.97(0.76Bi0.5Na0.5TiO3−0.24SrTiO3)−0.03NaNbO3 (BNT−ST−0.03NN) ceramics with an ergodic relaxor (ER) state, leading to a large normalized strain (d33*) of 720 pm/V. The introduction of NN templates into BNT−ST induces the grain orientation growth and enhances the ergodicity. The highly &lt;001&gt;-textured BNT−ST−0.03NN ceramics display a pure ergodic relaxor state with coexisted ferroelectric $$R\bar 3c$$ R 3 ¯ c and antiferroelectric P4bm polar nanoregions (PNRs) on nanoscale. Moreover, due to the incomplete interdiffusion between the NN template and BNT−ST matrix, the textured ceramics present a core-shell structure with the antiferroelectric NN core, and thus the BNT-based matrix owns more $$R\bar 3c$$ R 3 ¯ c PNRs relative to the homogeneous nontextured samples. The high &lt;001&gt; crystallographic texture and more $$R\bar 3c$$ R 3 ¯ c PNRs both facilitate the relaxor-to-ferroelectric transition, leading to the low-field-driven high strain, while the ergodic relaxor state ensures a small hysteresis. Furthermore, the d33* value remains high up to 518 pm/V at 100 °C with an ultra-low hysteresis of 6%.

Superior Large-Signal Piezoelectric Coefficient in Textured NBT-Based Piezoceramics by Template-Induced Structure and Composition Modulation

“…It can be considered that the polar nanoregions (PNRs) coalesce into larger domain-like structures in the nontextured sample because the NBT-BT-2.2FN ceramic at room temperature provides an NR state . For comparison, typical randomly scattered PNRs (marked by red arrows) can be observed, embedding in the ⟨001⟩-oriented textured ceramic (Figure g), which is similar to that reported for NBT-based materials. , This change in the microdomains is ascribed to the phase structure variations and the lattice distortions, leading to the disruption of the long-range order in the NBT lattices, producing highly dynamic and smaller PNRs in the textured ceramic. Furthermore, the corresponding selected area electron diffraction (SAED) patterns in the textured grain viewed along the [001] and [110] zone axis are provided in Figure h,i, respectively, which reveal the 1/2­{ooe}-type (characteristic of the tetragonal phase) and 1/2­{ooo}-type (indicative of the rhombohedral phase) superlattice spots coexist at room temperature .…”

“…Figure e displays the higher-magnification view of the area marked by a black circle, where the demarcation (indicated by the white dashed line) of the NN template and the matrix can be observed. Region 1 in Figure e presents the lattice fringes of the NN template that are long-range ordered and neatly aligned . In contrast, region 2 shows the lattice fringes of the textured matrix grown on the surface of the NN template, where almost no aligned order is observed, implying an increased ionic disorder in the matric after epitaxial crystal growth.…”

“…On the basis of previous studies, the field-induced phase transition is inherently associated with the crystallographic orientation and can be facilitated in the ⟨001⟩-crystallographic orientation. , For example, the (001) c -oriented NBT-6BT-2KNN single crystals can trigger the relaxor–ferroelectric phase transition at 40 kV/cm, which is much lower than that of the randomly oriented counterpart (70 kV/cm) . However, the main disadvantages of NBT-based single crystals are the synthesis cost and the severe composition segregation during crystal growth; therefore, it is difficult to apply the piezoelectric single crystals to large-scale manufacture. , Templated grain growth (TGG), as an alternative, is one of the most promising methods to achieve a single crystal-like nature by grain orientation engineering. − Based on the well-matched valence states and lattice parameters, the plate-like NaNbO 3 (NN) particles are usually chosen as templates added to induce grain orientation growth in the morphotropic phase boundary (MPB) region of NBT-based ceramics. , …”

Superior ferroelectric properties and enhanced depolarization temperature simultaneously achieved in BNT‐based ceramics

“…A promising ferroelectric materials used in the high‐power supplies should have a large P r , high electrical breakdown field ( E b ) and high depolarization temperature ( T d ), corresponding to the high output current, high output voltage, and good thermal stability, respectively 1,2,10,11 . The most widely investigated lead‐free ferroelectric systems were (K 0.5 Na 0.5 )NbO 3 , BaTiO 3 , and (Bi 0.5 Na 0.5 )TiO 3 (BNT) 12–16 . Compared with PZT95/5 ceramics, the BNT ceramics have higher P r , 9–12 meaning the generation of higher charge output.…”

“…1,2,10,11 The most widely investigated lead-free ferroelectric systems were (K 0.5 Na 0.5 )NbO 3 , BaTiO 3 , and (Bi 0.5 Na 0.5 )TiO 3 (BNT). [12][13][14][15][16] Compared with PZT95/5 ceramics, the BNT ceramics have higher P r , [9][10][11][12] meaning the generation of higher charge output. Recently, it is reported that BNT lead-free ceramics can generate a high current output (38 µC/cm 2 ) and high-power output (3.04 × 108 W/kg) under a high compression stress, which are higher than most ferroelectrics and thus shows potential for high-power applications.…”