Shaoxiong Xie

In this study, the effects of crucible-introduced elements (Al3+, Ti4+, Mg2+ and Y3+) on the structure, crystallization behavior, and electric properties of BaO-Bi2O3-TiO2-B2O3 glasses and glass-ceramics (GCs) were systematically investigated....

Aerosol‐deposited films display a reduced electromechanical response due to a grain size below 100 nm, deposition‐induced residual stresses, and conductivity due to local defects. Although heat treatment can facilitate grain growth, residual stress relaxation, and defect recombination, it limits the possible applications of aerosol deposition, especially for temperature‐sensitive substrates. Flash lamp annealing is utilized to selectively heat treat aerosol‐deposited barium titanate films with different thicknesses from 2 to 16 μm. Simulations and X‐ray diffraction indicate increasing temperature difference between the film surface and the substrate‐film interface up to 170 °C for the 16 μm‐thick film. While the relative permittivity can be improved by flash lamp annealing from 90 to 150 at 1 kHz and a 6 μm thickness, it still lags behind samples conventionally annealed at 500 °C, as the introduced thermal gradient can lead to surface cracks due to thermal stresses. Preannealing is proposed to reduce surface crack opening displacement compared to flash lamp annealed films. This supports the impact of remanent shrinkage during the first annealing cycle. While apparent challenges associated with the selective annealing of aerosol‐deposited films are discussed, flash lamp annealing remains a promising method for reducing annealing time and utilizing temperature‐sensitive substrates.

The origin of frequently observed ultrahigh electro-induced longitudinal strain, ranging from 1% to 26%, remains an open question. While recent studies have associated this phenomenon with bending deformation, the underlying mechanisms and the pronounced thickness dependence of the nominal strain have yet to be fully elucidated. Here, we demonstrate that the bending in piezoelectrics can be induced by a nonzero gradient of d_{31} across thickness direction. A scaling law (η_{3,nom}∝L^{2}E_{3}∇_{z}d_{31}/t) is derived to quantify the size dependence, thereby resolving longstanding ambiguities surrounding reported "giant" electrostrains. Simulations reveal that in standard perovskite piezoceramics, such as KNbO_{3}, a 0.69% concentration of oxygen vacancies can induce a 6.3 pC/N variation in d_{31} by suppressing polarization rotation, being sufficient to produce ultrahigh nominal strain in thin samples. Numerous factors, including gradients in defect concentration, composition, and stress, may lead to sufficient inhomogeneity in the distribution of d_{31}, suggesting electrobending may be a widespread phenomenon. This Letter presents a unified framework for understanding electrobending deformation, offering deeper insight into the mechanisms behind abnormally giant electrostrain responses in diverse piezoelectric systems and may encourage new engineering applications.

The macroscopic properties of ferroic materials are well-known to be influenced by their underlying domain dynamics. In ferroelectric ceramics, domain structures can be categorized into two main types: ferroelectric domains, associated with spontaneous polarization, and ferroelastic domains, linked to spontaneous strain. Currently, ferroelectric domains and their dynamic behaviors have been extensively studied, as they are recognized to directly influence the functionality of ferroelectric ceramics and determine the output performance of electronic devices. In contrast, the understanding of ferroelastic domain dynamics remains limited, primarily because ferroelastic deformation is only activated under mechanical loads of sufficient magnitude. Despite this, ferroelastic properties in ferroelectric ceramics must be considered in certain applications, such as piezoelectric multilayer actuators that are typically subjected to compressive preloads and high blocking forces. Under these loading conditions, ferroelastic deformation induces nonlinear behaviors and remanent strain, leading to degraded performance of ferroelectric ceramics and reduced stability and reliability of electronic devices. For this reason, deep understanding of ferroelasticity and deciphering mechanisms behind ferroelastic deformation in ferroelectric materials is essential for advancing material design and optimization to meet diverse application needs. This chapter explores the current understanding of ferroelastic properties and deformation mechanisms in representative ferroelectric materials under various loading conditions. Additionally, it highlights toughening effect related to ferroelasticity in ferroelectric materials that have been discovered in recent years. This knowledge could provide valuable insights for the development of the next generation of ferroic materials for a wide range of technological applications.

High‐entropy perovskite ferroelectric materials have attracted significant attention due to their remarkably low remnant polarizations and narrow hysteresis. Thus, these materials offer high‐energy density and efficiency, making them suitable for energy storage applications. Despite significant advancements in experimental research, understanding of the properties associated with structure remains incomplete. This study aims to study the structural, electric, and mechanical performances at various scales of the high‐entropy (Na _0.2 Bi _0.2 Ca _0.2 Sr _0.2 Ba _0.2 )TiO ₃ (NBCSB) material. The results of first‐principles calculations indicated that the pseudo‐intralayer distortion was obviously smaller compared to the interlayer distortion. Among the various bonds, Bi–O, Ca–O, and Na–O experienced the greatest displacement. Similarly, the hybridization between O 2p and Ti 3d states with Bi 6p states was particularly strong, affecting both the ferroelectric polarization and relaxor behavior. The NBCSB materials produced using a typical solid‐state process demonstrated exceptional performance in energy storage with a recoverable density of 1.53 J·cm ⁻³ and a high efficiency of 89% when subjected to a small electric field of 120 kV·cm ⁻¹ . In addition, these ceramics displayed a remarkable hardness of around 7.23 GPa. NBCSB ceramics exhibited exceptional relaxation characteristics with minimal hysteresis and low remanent polarization due to its nanoscale high dynamic polarization configuration with diverse symmetries (rhombohedral, tetragonal, and cubic) resulting from randomly dispersed A‐site ions. The excellent mechanical property is related to the dislocation‐blocking effect, solid solution strengthening effect, and domain boundary effect. The findings of this study offer a comprehensive and novel perspective on A‐site disordered high‐entropy relaxor ferroelectric ceramics.

Dielectric capacitors are employed extensively due to their exceptional performance, including a rapid charge-discharge speed and superior power density. However, their practical implementation is hindered by constraints in energy-storage density (ESD), efficiency (ESE), and thermal stability. To achieve domain engineering and improved relaxor behavior in 0.67BiFeO₃-0.33BaTiO₃-based Pb-free ceramics, the concerns have been addressed here by employing a synergistic high-entropy strategy involving the design of the composition of Sr(Mg_1/6Zn_1/6Ta_1/3Nb_1/3)O₃ with B-site multielement coexistence and high configuration entropy. Remarkably, in (0.67-x)BiFeO₃-0.33BaTiO₃-xSr(Mg_1/6Zn_1/6Ta_1/3Nb_1/3)O₃ ceramics with x = 0.08, a good ESE (η) of 75% and a recoverable ESD (W_rec) of 2.4 J/cm³ at 190 kV/cm were attained together with an ultrahigh hardness of ∼7.2 GPa. The high-entropy strategy, which is tailored by an increase in configuration entropy, can be attributed to the superior mechanical and ES properties. It also explains the enhanced random field and relaxation behavior, the structural coexistence of ferroelectric rhombohedral (R3c) and nonpolar pseudocubic (Pm-3m) symmetries, the decreased domain size, and evenly distributed polar nanoregions (PNRs). Moreover, improved thermal stability and outstanding frequency stability are also obtained. By boosting the configuration entropy, BiFeO₃-BaTiO₃ materials dramatically improved their complete energy storage performance. This suggests that designing high-performance dielectrics with high entropy can be a convenient yet effective technique, leading to the development of advanced capacitors.

Bismuth titanate (BIT) is widely known as one of the most prospective lead‐free ferroelectric and piezoelectric materials in advanced high‐temperature sensing applications. Despite significant advances in developing BIT ferroelectrics, it still faces major scientific and engineering challenges in realizing super‐high performance to meet next‐generation high‐sensitivity and light‐weight applications. Here, a novel ferroelectric domain‐engineered BIT ceramic system is conceived that exhibits super‐high piezoelectric coefficient (d₃₃ = 38.5 pC N⁻¹) and inverse piezoelectric coefficient (d₃₃^* = 46.7 pm V⁻¹) at low electric field as well as excellent fatigue resistance (stable up to 10⁷ cycles). The results reveal that the introduction of high‐density layered (001)‐type 180° domain walls with flexible polarization rotation features and the formation of small‐size multi‐domain states with low energy barriers are mainly responsible for the excellent electrical performance. To the best of knowledge, it is the first time to reveal such intriguing domain structures in BIT ceramics in detail, especially from the atomic‐scale perspective by using atomic number (Z)‐contrast imaging in combination with atomic‐resolution polarization mapping. It is believed that this breakthrough conduces to comprehensively understand structural features of ferroelectric domains in BIT ceramics, and also opens a window for future developments of super‐high performance in bismuth layer‐structured ferroelectrics via domain engineering.

Taking Bismuth Titanate (Bi₄Ti₃O₁₂) as a Aurivillius-type compound with m = 3 for example, the ion (W⁶⁺/Cr³⁺) doping effect on the lattice distortion and interlayer mismatch of Bi₄Ti₃O₁₂ structure were investigated by stress analysis, based on an elastic model. Since oxygen-octahedron rotates in the ab-plane, and inclines away from the c-axis, a lattice model for describing the status change of oxygen-octahedron was built according to the substituting mechanism of W⁶⁺/Cr³⁺ for Ti⁴⁺, which was used to investigate the variation of orthorhombic distortion degree (a/b) of Bi₄Ti₃O₁₂ with the doping content. The analysis shows that the incorporation of W⁶⁺/Cr³⁺ into Bi₄Ti₃O₁₂ tends to relieve the distortion of pseudo-perovskite layer, which also helps it to become more stiff. Since the bismuth-oxide layer expands while the pseudo-perovskite layer tightens, an analytic model for the plane stress distribution in the crystal lattice of Bi₄Ti₃O₁₂ was developed from the constitutive relationship of alternating layer structure. The calculations reveal that the structural mismatch of Bi₄Ti₃O₁₂ is constrained in the ab-plane of a unit cell, since both the interlayer mismatch degree and the total strain energy vary with the doping content in a similar trend to the lattice parameters of ab-plane.

A sort of tungsten/chromium(W/Cr) co-doped bismuth titanate (BIT) ceramics (Bi₄Ti_2.95W_0.05O_12.05 + 0.2 wt % Cr₂O₃, abbreviate to BTWC) are ordinarily sintered between 1050 and 1150 °C, and the indentation behavior and mechanical properties of ceramics sintered at different temperatures have been investigated by both nanoindentation and microindentation technology. Firstly, more or less Bi₂Ti₂O₇ grains as the second phase were found in BTWC ceramics, and the grain size of ceramics increased with increase of sintering temperatures. A nanoindentation test for BTWC ceramics reveals that the testing hardness of ceramics decreased with increase of sintering temperatures, which could be explained by the Hall–Petch equation, and the true hardness could be calculated according to the pressure-state-response (PSR) model considering the indentation size effect, where the value of hardness depends on the magnitude of load. While, under the application of microsized Vickers, the sample sintered at a lower temperature (1050 °C) gained four linearly propagating cracks, however, they were observed to shorten in the sample sintered at a higher temperature (1125 °C). Moreover, both the crack deflection and the crack branching existed in the latter. The hardness and the fracture toughness of BTWC ceramics presented a contrary variational tendency with increase of sintering temperatures. A high sintering tends to get a lower hardness and a higher fracture toughness, which could be attributed to the easier plastic deformation and the stronger crack inhibition of coarse grains, respectively, as well as the toughening effect coming from the second phase.