BT Ceramics Research Articles

Investigation of electrocaloric effect and scaling behavior with correlation of structural, electrical, and impedance properties in Sn-substituted NBT–BT ceramics near MPB

Abstract Bismuth ferrite–barium titanate (BF–BT)‐based ceramics exhibit outstanding strain and piezoelectric properties, making them crucial for various applications. However, the simultaneous enhancement of the piezoelectric coefficient and electrostrain remains challenging, and the physical mechanisms underlying property enhancement remain unclear. To realize comprehensive property optimization and deepen the understanding of the physical mechanisms in BF–BT ceramics, this study incorporates a third component, bismuth sodium titanate, into BF–BT‐based ceramics. A large electrostrain (S = 0.34% @120 kV/cm) with a slightly reduced d33 can be obtained in ceramics with x = 0.03, breaking the conventional tradeoff between d33 and strain in relaxor ferroelectrics with nanodomains. The high d33 was attributed to the rhombohedral/pseudocubic phase coexistence and the enhanced intrinsic reversible contribution. The large strain originated from the extrinsic contribution of easier domain switching, as evidenced by the enhanced polarization and ferroelectric scaling behavior.

High-piezoelectric lead-free BiFeO3–BaTiO3 ceramics with enhanced temperature stability and mechanical properties

Advancing piezoelectricity and excellent thermal stability: <001>-textured 0.75BF–0.25BT lead-free ceramics for high temperature applications

Abstract In recent years, bismuth ferrite‐based (BiFeO3‒BaTiO3) lead‐free piezoelectric ceramics have garnered extensive research attention. This is attributed to their high Curie temperature, rendering them promising candidates for high‐temperature piezoelectric device applications. Nevertheless, attaining synergistic piezoelectric performance within BiFeO3‒BaTiO3 ceramics remains a formidable challenge. In this study, BiGaO3 was incorporated into the BiFeO3‒BaTiO3 matrix. A systematic investigation and discussion were carried out regarding the phase structures, microstructures, ferroelectric properties, piezoelectric properties, and dielectric properties of the fabricated materials. The synthesized ceramics were deliberately engineered to establish a rhombohedral and pseudo‐cubic phase boundary, which serves as a fundamental prerequisite for enhancing piezoelectric properties. Due to the synergistic impacts of appropriate BiGaO3 doping, the 0.69BFG0.025‒0.31BT ceramics achieved favorable piezoelectric performance characteristics, including a piezoelectric coefficient (d33) of 254 pC/N, a Curie temperature of 472°C, and a high depolarization temperature of 545°C. These results affirm that this material holds great potential for applications in high‐temperature piezoelectric devices.

Abstract The pursuit of environmentally sustainable, lead‐free ceramics with outstanding energy storage capabilities is crucial for the advancement of next‐generation high‐power capacitors. However, achieving this objective comes with significant hurdles. In this investigation, we have developed a highly effective method for inducing the relaxor ferroelectric phase (RFE) within super paraelectric (SPE) materials, specifically in Bi3+‐substituted NBT‐BT‐CLT ceramics. This innovation has resulted in an exceptional energy storage density of approximately 5.83 J cm−3 under an electric field of 320 kV/cm, coupled with an impressive efficiency rating of around 79%. The outstanding performance in energy storage can be largely attributed to the intentional manipulation of ultrasmall polar nanoregions, as confirmed through HRTEM analysis. This engineering approach not only reduces grain size but also significantly enhances polarization and raises the thresholds for the breakdown of electric fields. The SPE‐RFE strategy demonstrated in this study holds broad applicability in optimizing dielectric properties and other essential functionalities, thereby facilitating the conceptualization of advanced energy storage devices.

ABSTRACT Advancements in technology and the need for compact electronics have raised the demand for materials with both high energy-storage density and electric-field induced strain. In this study, lead-free (Bi0.465Na0.465Ba0.07)Nb x Ti(1–x)O3 piezoelectric ceramics, x = 0–0.05, were prepared by conventional solid-state reaction method. All samples exhibited single-phase perovskite structure, with Rietveld refinement revealing the coexistence of tetragonal (P4bm) and rhombohedral (R3c) phases. Increasing Nb content lowered T F-R below room temperature at x ≥0.02, indicating a transition from non-ergodic relaxor (NER) to ergodic relaxor (ER) phase. This phase shift resulted in a maximum strain of 0.27%, corresponding to normalized strain (d 33*= S max/E max) of 386 pm/V at 70 kV/cm, achieved at x = 0.01. Additionally, Nb doping significantly increased resistivity (~1 order of magnitude) and activation energy (E a) values, thereby enhancing electrical breakdown strength (E b). This, combined with decreasing P r to near-zero from ergodic relaxor, led to a remarkably high energy density (W rec) of 1.73 J/cm3 and an energy storage efficiency (η) of 82% under a relatively low electric field of 130 kV/cm at x = 0.04. These results demonstrated that optimal Nb doping can simultaneously improve the electro-strain and energy-storage performance of 0.93BNT–0.07BT ceramics, making them promising for actuator and energy-storage applications.

In lead-free (Bi0.5Na0.5)TiO3–BaTiO3 (BNT–BT) ceramics, the BNT-rich side has R3c ferroelectric domains at room temperature, and modulated P4bm tetragonal nanodomains develop within the R3c rhombohedral phase at approximately the depolarization temperature Td. Such structural phase transitions have conventionally been modulated by doping with additives or by controlling the composition. However, it is considered that the coexistence region between the R3c and P4bm phases is important for enhancing the energy storage behavior because the phase reversal between them, caused by the electric field, can cause the BNT-based ceramics to exhibit an antiferroelectric-like pinched hysteresis loop. In this study, the structural phase transition of BNT–BT ceramics is promoted through process control, that is, by adjusting the cooling rate, and then the stabilization of the P4bm phase and the expansion of the coexistence region of the R3c and P4bm phases were examined, which results in enhanced energy storage behavior. Consequently, BNT–BT ceramics prepared at a slower cooling rate (0.01 °C s−1) than that of normal firing (0.05 °C s−1) demonstrate the stabilization of the P4bm phase and expansion of the coexistence region of the R3c and P4bm phases. Therefore, process control modulates the structural phase transition, which can cause enhanced energy storage behavior.

BiFeO3–BaTiO3 (BF–BT) is one of the lead-free piezoceramic materials with high Curie temperature (TC) and high polarization. Herein, the (Bi0.5Li0.5Ti)6+ group elements are introduced into the 0.75BiFeO3−0.25BaTiO3 (0.75BF–0.25BT) system to optimize comprehensive performances via optimizing the intrinsic piezoelectric contribution and the extrinsic piezoelectric contribution. For intrinsic piezoelectric contribution, the tetragonal phase ratio of the ceramics is increased. For extrinsic piezoelectric contribution, the grain structures and the domain structures of the ceramics are improved with a relaxor state in which small-sized domains and large-sized domains coexist. The best overall performances are obtained at x = 0.010 with piezoelectric constant d33 ∼ 130 pC/N at room temperature, d33 ∼ 231 pC/N at 313 °C, resistance ρ ∼ 1.49 × 106 Ω cm at 300 °C, and Curie temperature TC ∼ 632 °C that improved significantly. Moreover, when x = 0.010, the piezoelectric thermal stability is also significantly improved, with Δd33 being less than 15% before 200 °C and maintaining 60% of d33 at 400 °C. The present experiments provide a new strategy to investigate the origin of the enhanced piezoelectric response of BF–BT ceramics as well as their applications in the field of high-temperature lead-free piezoelectricity.

The BiFeO3-BaTiO3 (BF-BT) ceramics were here prepared through the solid-state reaction of Bi2O3, Fe2O3 and nano-sized BT powders. The crystal structures and piezoelectric properties were investigated in both quenched (AQ) and slowly cooled (SC) 0.7BF-0.3BT ceramics. Prior work has shown that rhombohedral and pseudo-cubic phases coexist in 0.7BF-0.3BT ceramics. In this work, the crystal structure of the pseudo-cubic phase was refined as a non-polar orthorhombic Pbnm phase in the SC sample and as a polar orthorhombic Pmc21 phase in the AQ sample. In addition to a sharp dielectric peak at about 620 °C, corresponding to the Curie temperature of the rhombohedral phase, a broad dielectric peak with strong frequency dispersion and a sharp frequency-independent dielectric peak were observed at around 500 °C in the SC and AQ samples, respectively. We determine that the dielectric anomalies around 500 °C were caused by a relaxor phase transition of the non-polar orthorhombic phase in the SC sample and a ferroelectric-paraelectric phase transition of the polar orthorhombic phase in the AQ sample. The AQ sample showed better ferroelectric and piezoelectric properties than the SC sample. The 0.7BF-0.3BT ceramic slowly cooled in a nitrogen atmosphere showed a well-saturated P-E curve and a similar temperature-dependent dielectric constant as the AQ sample. Our results indicate that large concentrations of oxygen vacancies produce a more distorted polar orthorhombic phase and better piezoelectric properties in the AQ sample than in the SC sample.

Low temperature sintering and enhanced piezoelectric properties of BiFeO3–BaTiO3 ceramics by homogeneous calcination

Abstract Dielectric capacitors, which can achieve tremendous power density and ultrafast charge/discharge speed, are crucial components for high power equipment. Yet, the synchronous achievement in high recoverable energy density (Wrec) and high efficiency (η) is a long‐term difficulty for dielectric ceramics. Herein, the (0.85 − x)NaNbO3–0.15BaTiO3–xBi(Mg1/3Ta2/3)O3 (NN–BT–xBMT) relaxor ferroelectric ceramics were proposed and studied. The doping of BMT was conducive to promoting the microstructure and bandgap and improving the dielectric relaxation properties of NN–BT ceramics. Finally, the sample of x = 0.10 presented a high Wrec of 5.9 J/cm3 and a high η of 90% simultaneously. In addition, the sample also exhibited superb charge/discharge performances with large power density (PD = 137 MW/cm3) and fast charge/discharge speed (t0.9 = 39 ns). The above results reveal that the NaNbO3‐based ceramics could serve as potential alternatives for advanced dielectric capacitors.

Tuning the electrical conductivity and Maxwell-Wagner relaxation in BiFeO3–BaTiO3 piezoceramics

BiFeO3–BaTiO3 (BF–BT) ceramics with high Curie temperature and excellent piezoelectric coefficient are expected to be applied in high-temperature piezoelectric sensors and actuators. However, its resistivity decreases rapidly with temperature and impedes its further applications. Moreover, normal methods such as doping modification cannot address this issue. In the present work, bismuth layered Bi4Ti2.93(Zn1/3Nb2/3)0.07O12 (BIT) and perovskite 0.36BiScO3-0.64PbTiO3 (BSPT) ceramics were selected as insulating layers and were, respectively, sintered with 0.7BF–0.3BT ceramics to form laminated ceramics. The heterojunction structures effectively prevent carrier migration, and both resistivities of BIT and BSPT laminated ceramics were increased from 106 to 108−9 Ω cm at 300 °C. In addition, piezoelectric properties of the BSPT-type laminated ceramics are much higher than that of BF–BT ceramics, in which the bipolar strain was increased from 0.04% to 0.1% (4 kV/mm), and d33 was increased from 140 to 237 pC/N. Therefore, designing the insulating layer may be an effective method to realize the high-temperature application for BF–BT ceramics.

Synthesis and performance of tetragonal Ca2+ doped BaTiO3 fine powders

Abstract The electrostrain properties of bismuth ferrite–barium titanate (BF–BT)‐based ceramics can be well regulated; however, this often occurs at the cost of piezoelectricity, and their electrostrain‐temperature stability is poor. To address these problems, defect engineering has been utilized to enhance the comprehensive properties via the unequal substitution of Na+. In this study, 0.69BiFeO3–0.3BaTiO3–0.01NaxNbO3 (BF–BT–NxN) (x = 0.8, 0.9, 1, 1.1, and 1.2) ceramics with different defect concentrations were prepared. Enhanced piezoelectricity and electrostrain (d33 = 165 pC/N and S = ∼0.22%, respectively) were obtained for the BF–BT–N0.9N ceramic. In particular, excellent temperature stability with a strain variation of only 12% from room temperature to 180°C was achieved. The introduction of NaxNbO3 reduced the degree of distortion of the oxygen octahedron, and the defects altered the local structure and heightened its disorder, leading to an enhancement in both the electrostrain and piezoelectric properties. In addition, the temperature‐dependent evolution of the oxygen octahedron structure was altered by defect engineering. A mutual compensation mechanism for the contribution of structural evolution and domain wall motion to electrostrain has been proposed to explain the excellent temperature stability.

Abstract In many studies, the properties of BiFeO3–BaTiO3 (BF–BT) ceramics vary greatly using different raw reagents, which makes it challenging to obtain reliable and repeatable properties of BF–BT‐based devices. In this work, 0.7BiFeO3–0.3BaTiO3 (0.7BF–0.3BT) ceramics were fabricated by a conventional solid‐phase synthesis using TiO2 reagents with varied purities of 98%, 99%, 99.9%, and 99.99%, respectively. The phase structure, microstructure, ferroelectric, and piezoelectric properties were comprehensively studied. All compositions of the ceramics exhibit a pseudo‐cubic phase perovskite structure, and the fraction of the rhombohedral phase increases with increasing the TiO2 purity. Additionally, backscattered electron images and energy‐dispersive spectroscopy revealed an obvious core–shell structure within grains. In particular, the 0.7BF–0.3BT ceramics prepared with 98% purity TiO2 exhibited superior ferroelectric and piezoelectric properties, d33 ∼ 220 pC/N and ∼ 230 pm/V. The ceramics prepared with higher purity TiO2 suffered from severe leakage conduction, which can be well addressed by adding excess TiO2. Our work reveals the importance of different grades of purity TiO2 on the electrical properties of BF–BT ceramics.

Phase diagrams of BiFeO3-BaTiO3 (BF–BT) thin films were constructed via thermodynamic model calculation, as well as their electrical properties. The calculated morphotropic phase boundary (MPB) of BF–BT thin films without strain is located near the composition of 0.663BF–0.337BT, which agrees well with the experimental results of reported BF–BT ceramics (between 0.66BF–0.34BT and 0.71BF–0.29BT). The permittivity, tunability and [Formula: see text]of BF–BT thin films on Si substrates are higher than those on SrTiO3(ST) plates, which are also in accordance with the measured data in the literature. Further calculation indicates that 0.7BF–0.3BT and 0.6BF–0.4BT thin films can achieve enormous piezoelectric coefficient [Formula: see text] ([Formula: see text]1200 and [Formula: see text]1000 pm/V, respectively) by selecting the substrates with the TEC respectively of 0.3 and 3.1 × 10[Formula: see text]/[Formula: see text]C, because of the phase transition from aa phase to rhombohedral phase. Such results help to clarify the phase diagrams of BF–BT thin films, implying that huge [Formula: see text]can be achieved by choosing the composition near MPB on the substrates with small TEC.

Among the lead-free piezoceramics, ([Formula: see text])BiFeO[Formula: see text]BaTiO3 (BF-BT) is considered a promising candidate for high-temperature piezoelectric materials owing to its high Curie temperature ([Formula: see text]C) and good electromechanical properties. In this work, the hydrothermal synthesis method was used to prepare the precursor powders of BiFeO3 and BaTiO3, and then the mixed powder compacts with the chemical composition of 0.7BF–0.3BT were sintered under pressureless conditions. The influence of the hydrothermal reaction times (12–24[Formula: see text]h) of BiFeO3 on the structures and electric properties of the sintered ceramics was instigated. First, all the samples synthesized with the tetragonal BaTiO3 and BiFeO3 powders were identified with relatively stable dielectric properties. As the hydrothermal reaction time to synthesize BiFeO3 increased, the dielectric properties as well as the temperature stability of the 0.7BiFeO3–0.3BaTiO3 ceramics also improved. At the condition of a hydrothermal reaction time of 24[Formula: see text]h, the sample obtained possesses both the lowest temperature coefficient of dielectric constant ([Formula: see text]C between RT and [Formula: see text]C) and the highest Curie temperature ([Formula: see text]C at 100[Formula: see text]kHz). Moreover, at high temperatures, it exhibits a higher AC impedance than others. The calculating result based on the resistive constant-phase-element model (R-CPE) circuit model showed that the grain boundary of the 0.7BF–0.3BT ceramics contributes more resistance to the conductivity at high temperatures. In summary, the hydrothermal reaction proved to be a useful way that achieves the preparation of single-phase 0.7BF–0.3BT ceramics with improved electrical properties.

Lead-free ceramics based on bismuth sodium lanthanum titanate (Bi0.4871Na0.4871La0.0172TiO3: BNLT) and barium titanate (BaTiO3: BT) were prepared by a modified two-step mixed-oxide method. Effects of BT content on the phase transition, thermal expansion behavior, mechanical and electrical properties of lead-free BNLT-BT ceramics were studied. The Burn’s temperature and local polarizations were estimated from the thermal expansion data. Various aspects of understanding the polarization behavior and other effects in this system have also been investigated and discussed. The 0.96BNLT-0.04BT ceramics have shown the d33 value of 135 pC/N. The coercive field (E c) and remanent polarization (P r) were found to be 24 kV/cm and 9.0 µC/cm2, respectively. This may be useful in the future development of multifunctional lead-free materials in electronic applications.