Ergodic Relaxor Phase Research Articles

Ultrahigh Electrostrictive Effect in Lead-Free Sodium Bismuth Titanate-Based Relaxor Ferroelectric Thick Film.

In recent years, the development of environmentally friendly, lead-free ferroelectric films with prominent electrostrictive effects have been a key area of focus due to their potential applications in micro-actuators, sensors, and transducers for advanced microelectromechanical systems (MEMS). This work investigated the enhanced electrostrictive effect in lead-free sodium bismuth titanate-based relaxor ferroelectric films. The films, composed of (Bi0.5Na0.5)0.8-xBaxSr0.2TiO3 (BNBST, x = 0.02, 0.06, and 0.11), with thickness around 1 μm, were prepared using a sol-gel method on Pt/TiO2/SiO2/Si substrates. By varying the Ba2+ content, the crystal structure, morphology, and electrical properties, including dielectric, ferroelectric, strain, and electromechanical performance, were investigated. The films exhibited a single pseudocubic structure without preferred orientation. A remarkable strain response (S > 0.24%) was obtained in the films (x = 0.02, 0.06) with the coexistence of nonergodic and ergodic relaxor phases. Further, in the x = 0.11 thick films with an ergodic relaxor state, an ultrahigh electrostrictive coefficient Q of 0.32 m4/C2 was achieved. These findings highlight the potential of BNBST films as high-performance, environmentally friendly electrostrictive films for advanced microelectromechanical systems (MEMS) and electronic devices.

Innovative Design of BNKT-xSLZT Ceramics: Maximizing the Polarization Difference for Enhanced Energy Storage.

Lead-free relaxor ferroelectric ceramics with outstanding energy-storage (ES) density (Wrec) and high ES efficiency (η) are crucial for advanced pulse-power capacitors. This study introduces a strategic approach to maximizing the polarization difference (ΔP) by inducing a transition from the ferroelectric phase to the ergodic relaxor (ER) phase. By employing this strategy, a series of ceramics, (1 - x)(Bi0.5Na0.4K0.1)TiO3-x(Sr0.85La0.1)(Zr0.5Ti0.5)O3 (BNKT-xSLZT), with varying SLZT content (x = 0.05, 0.10, 0.15, and 0.20), were designed. The addition of SLZT enhances cationic disorder, induces vacancies at A sites, and disrupts long-range ferroelectric order, facilitating the formation of polar nanoregions and enhancing relaxor ferroelectric behavior. Furthermore, a viscous polymer process (VPP) technology is employed to optimize the ceramics' structure, aiming to increase the breakdown strength (Eb) and enhance ΔP. Ultimately, enhanced ES performance is demonstrated in BNKT-0.15SLZTVPP, achieving a remarkable Wrec of 6.85 J/cm3 and η of 84% under 470 kV/cm. This composition demonstrates excellent stability with minimal variations in Wrec (3.0%) and η (4.4%) over the temperature range of 20-110 °C. Additionally, BNKT-0.15SLZTVPP exhibits exceptional pulse charge-discharge properties, featuring a high discharge density of 3.72 J/cm3, a large power density of 164.2 MW/cm3, and a short discharge time (t0.9) of 193 ns under 300 kV/cm. The study validates the practicality of BNKT-0.15SLZTVPP for pulse capacitors and underscores the potential to enhance ES performance through A-site donor doping and VPP technology. This work provides a comprehensive understanding of the interplay among composition, structure, and ES properties in lead-free relaxor dielectric ceramics, laying the groundwork for innovative advancements in the field.

Improvement of electrostrain properties of BNT-based piezoelectric ceramics by co-doping of Sr2+ and Ta5+ in A and B sites

Lead-free piezoelectric ceramics of the [0.852(Bi0.5-xSrxNa0.5)-0.11(Bi0.5K0.5)-0.038Ba]Ti(1-x)TaxO3 (designated as BNKT-BT-xTaSr) ternary system were prepared with co-doping of Ta5+ and Sr2+. The purpose of this study is to investigate the effects of co-doping of Ta and Sr element on the microstructure, phase structure electrical properties, and electrostrain behavior of BNKT-BT-xTaSr ceramics. With the increase of Ta5+ and Sr2+ doping, the transition temperature (TF-R) of the modified doped BNKT-BT-xTaSr ceramics from ferroelectric to relaxed phase decreases to below room temperature (RT). When x = 0.005, the BNKT-BT-xTaSr ceramics reached a large electrostrain of 0.46%(d*33 = 657 p.m./V) at RT under an electric field of 7 kV/mm, which is caused by the transition from ergodic relaxor phase to ferroelectric phase under a high applied electrical field. In addition, the electrostrain is increased to 0.48% (d*33 = 685 p.m./V) under the same electric field after the thermal aging process at 80 °C for two weeks. This study demonstrates that the A/B site co-doping could effectively improve the electrostrain properties of BNKT-BT-xTaSr ferroelectric ceramics.

High-Temperature Energy Storage Properties of Bi0.5Na0.5TiO3-0.06BaTiO3 Thin Films

Bi0.5Na0.5TiO3-0.06BaTiO3 (BNT-BT) thin films were prepared via both chemical solution (CSD) and pulsed laser deposition (PLD). The structural, dielectric, and ferroelectric properties were investigated. High stability of the dielectric permittivity or TCC (∆ε/ε (150 °C) ≤ ±15%) over a wide temperature range from room temperature to 300 °C was obtained. Distinctly, the CSD film showed high TCC stability with variation of ±5% up to 250 °C. Furthermore, the CSD film showed an unsaturated ferroelectric hysteresis loop characteristic of the ergodic relaxor phase. However, the PLD one exhibited an almost saturated loop characteristic of the coexistence of both ergodic and non-ergodic states. The energy storage properties of the prepared films were determined using P–E loops obtained at different temperatures. The results show that these films exhibited a stable and improved energy storage density comparable to ceramic capacitors. Moreover, the CSD film exhibited more rigidity and better energy storage density, which exceeded 1.3 J/cm3 under a weak applied field of 317 kV/cm, as well as interesting efficiency in a large temperature range. The obtained results are very promising for energy storage capacitors operating at high temperatures.

Electric field-temperature phase diagram and electrical properties of (1-x)Na0.5Bi0.5TiO3 - xK0.5Bi0.5TiO3 ceramics

Electrically and thermally induced transitions between ferroelectric and relaxor states are of great significance in Na1/2Bi1/2TiO3 (NBT)-based materials due to their remarkable similarity to electromechanical properties. However, an in-depth understanding of the family of this material remains challenging, primarily due to its structural complexity and diverse behaviour with or without the presence of an external electric field. For enhancing NBT-based ceramics and enabling the analysis of their electric field temperature (E-T) phase diagrams, it has been suggested that K0.5Bi0.5TiO3 (KBT) could be used as a dopant material. This study thoroughly examines the electrical, microstructural, and ferroelectric (FE) properties of (1-x)NBT-xKBT ceramics. The incorporation of KBT into NBT, inducing a change in structural symmetry, reveals the coexistence of rhombohedral and tetragonal phases (x ∼ 0.2), as confirmed by X-ray diffraction. Using a modified KWW function, electrical modulus (EM) analysis illustrates a non-Debye-type relaxation process. Moreover, it is observed that temperature influences the transition of the material among its ferroelectric (FE), ergodic (ER), and non-ergodic (NR) relaxor phases. This report proposes that the E-T phase diagram can serve as a valuable tool for determining optimal conditions and selecting materials for electromechanical and actuator-based applications.

Optimized Strain Response in (Co0.5Nb0.5)4+-Doped 76Bi0.5Na0.5TiO3-24SrTiO3 Relaxors

High strain with low hysteresis is crucial for commercial applications in high precision actuators. However, the clear conflict between the high strain and low hysteresis in BNT-based ceramics has long been an obstacle to actual precise actuating or positioning applications. To obtain piezoceramics with high strain and low hysteresis, it is necessary to enhance the electrostrictive effect and develop an ergodic relaxor (ER) and nonergodic relaxor (NR) phase boundary under ambient conditions. In this work, (Co0.5Nb0.5)4+ doped 76Bi0.5Na0.5TiO3-24SrTiO3 (BNST24) relaxors were fabricated using the conventional solid state reaction route. X-ray diffraction patterns revealed the B-site substitution in BNST24 ceramics. By adjusting the (Co0.5Nb0.5)4+ doping in BNST24, we effectively tuned the TNR-ER and Td close to ambient temperature, which contributed to the development of the ergodic relaxor phase and enhanced the electrostrictive effect at ambient temperature. The I-P-E loops and bipolar strain curves verified the gradual evolution from NR to ER states, while the enhanced electrostrictive effect was verified by the nearly linear S-P2 curves and improved electrostrictive coefficient of the BNST24-xCN relaxors. An enhanced strain of 0.34% (d*33 = 483 pm/V) with low hysteresis of 8.9% was simultaneously achieved in the BNST24-0.02CN relaxors. The enhanced strain was mainly attributed to the proximity effect at the ER and NR phase boundary of BNST24-0.02CN, while the improved electrostrictive effect contributed to the reduced strain hysteresis. Our work demonstrates an effective strategy for balancing the paradox of high strain and low hysteresis in piezoceramics.

Improved capacitive energy storage capability of P(VDF-HFP) nanocomposites enabled by cost-effective and ergodic relaxor phase dominant nanofillers

Polymer-based dielectrics with excellent processability are essential for dielectric capacitors applications in modern electronics and electrical power systems. Although significant advances in capacitive storage have been achieved by adding inorganic fillers that are synthesized primarily by liquid-phase technology, this method faces considerable challenges for the industrial production of scalable capacitor films that requires easy process conditions. Herein, P(VDF-HFP) nanocomposites with cost-effective inorganic 0.7[0.955(Bi0.5Na0.5)TiO3-0.045Ba(Al0.5Ta0.5)O3]-0.3CaTiO3 nanoparticles (BNT-BAT-CT nps) that are prepared by a combination of solid phase approach and sieving, are constructed via a scalable and practical mechanical process. Both experimental and simulation results verify that the appropriate BNT-BAT-CT nps can significantly suppress the leakage current density, improve the dielectric constant, and block the penetration of the electrical tree, thus generating substantial enhancements in the breakdown strength and capacitive performance. A large discharge energy density (∼10.82 J/cm3) is realized at 580 MV/m in 3 vol% BNT-BAT-CT/P(VDF-HFP) nanocomposites, which is approximately 2.17 times larger than that of pristine P(VDF-HFP). More significantly, unlike previous polymer nanocomposites incorporated with high-cost nanofillers, the designed nanocomposites contain low preparation cost of nanofillers. Combined with the merits of high energy-storage performance and simple and cost-effective preparation, this work offers a viable method towards the large-scale production of polymer-based high-performance dielectrics.

Enhanced electro-strain with high electrostrictive performances of Bi0.5Na0.4K0.1TiO3 based lead-free piezoelectric ceramics by Ba(Fe0.5Nb0.5)O3

Complex piezoelectric ceramics of (1-x)[0.97(Bi0.5Na0.4K0.1)TiO3–0.03(Ba0.7Sr0.3)TiO3]-xBa(Fe0.5Nb0.5)O3 or (1-x)[0.97BNKT-0.03BST]-xBFN were investigated, where the x value was between 0 and 0.03. All compositions were synthesized via a conventional mixed oxide method. X-ray diffraction and Raman spectroscopy techniques indicated that all ceramics exhibited a coexistence of rhombohedral (R) and tetragonal (T) phases without any impurity phase. However, the T phase became dominant at higher BFN contents. The maximum temperature (Tm), the ferroelectric to ergodic relaxor phase transition temperature (TF-R), and Burn’s temperature (TB) decreased with increasing BFN content, while the dielectric constant at Tm was enhanced for the x = 0.01 ceramic. The BFN additive interrupted ferroelectric ordering, which led to constriction in the hysteresis loops as well as large electric field-induced strains (Smax = 0.42%), a normalized strain coefficient (d*33 = Smax/Emax = 846 pm/V), and an electrostrictive coefficient (Q33 = 0.0432 m4/C2) for the x = 0.01 ceramic under a moderate applied electric field of 50 kV/cm. These results indicated that this ceramic had the potential for electromechanical applications.

Effect of Chemical Inhomogeneity on the Dielectric and Impedance Behaviors of Bismuth Sodium Titanate Based Relaxors

Different levels of Nb2O5 substitution in 0.66(Bi0.5Na0.5)TiO3−0.06BaTiO3−0.28(Bi0.2Sr0.7)TiO3 (BS-xNb) lead-free relaxors were prepared to investigate the effect of chemical heterogeneity on the dielectric and impedance behaviors. X-ray diffraction reveals that the secondary phase gradually increases in number and intensity as the dopant increases. The substitution of less Nb5+ for Ti4+ leads to reduced electronic conductivity and dielectric loss, which is attributed to the inhibition of oxygen vacancies and associated electron. It is found that more valence electron defects are generated to cause charge leakage by introducing excess Nb2O5. Moreover, the addition of Nb2O5 doping enhances the disorder and facilitates the transition of the nonergodic to ergodic relaxor phase. The ferroelectric ergodic long-range order is further disrupted and promotes the formation of local defect fields and high-temperature polar nanoregions. These effects enhance the relaxation behavior with decreased remnant polarization and form a broadly flat dielectric platform. Meanwhile, BS-2Nb exhibits attractively high recoverable energy storage density and efficiency at a relatively low electric field with stability against frequency and temperature. Combined with the complex impedance characteristics, the leakage contribution of the chemical inhomogeneity introduced by excess Nb2O5 is presented, demonstrating the significance of regulating the dielectric performance of bismuth sodium titanate-based relaxors.

Optimizing strain response in lead-free (Bi0.5Na0.5)TiO3-BaTiO3-NaNbO3 solid solutions via ferroelectric / (non-)ergodic relaxor phase boundary engineering

Lead-free bismuth sodium titanate (Bi0.5Na0.5)TiO3 (BNT) and related solid solutions are potential piezoelectric materials for such applications as actuators and transducers if their excellent strain responses and piezoelectric properties can be optimized. In this work, a large strain response of 0.61% is achieved in lead-free (0.94-x%)(Bi0.5Na0.5)TiO3-0.06BaTiO3-x%NaNbO3 (x = 0 –6, BNT-6BT-xNN) ceramics with the composition of x = 3.5 in a pseudo-cubic structure. Coexistence of ferroelectric (FE) and relaxor (RE) domain structures is observed in all the unpoled ceramics and the enhanced strain response is believed to be related to the evolution of the ergodic relaxor (ER) and non-ergodic (NR) states thanks to the substitution of antiferroelectric NN. BNT-6BT-3.5NN is a critical composition near the FE/NR/ER phase boundary close to room temperature (RT) and its high strain response arises from a synergistic combination of a reversible electric-field-induced phase transition and an active domain switching in the mixed NR/ER state. This work provides new insights into the dynamic interplay between mesoscopic domains and macroscopic electrical properties in the BNT-based piezoceramics.

Phase transition and energy storage properties of Bi0.5Na0.5TiO3–Bi(Mg2/3Nb1/3)O3 lead-free ceramics

Bi0.5Na0.5TiO3 (BNT) lead-free ceramics have been extensively studied due to their excellent dielectric, piezoelectric and ferroelectric properties. The phase structure and functionalities of BNT can be feasibly adjusted by doping/forming solid solutions with other elements/components. In this work, Bi(Mg2/3Nb1/3)O3 (BMN) was introduced into BNT by a conventional solid-state reaction to form a homogeneous solid solution of (1-x)(Bi0.5Na0.5)TiO3-xBi(Mg2/3Nb1/3)O3 (BNT-xBMN) with a perovskite structure. With the increase of BMN content, a phase transition from rhombohedral R3c to tetragonal P4bm has been confirmed by XRD, along with shifting the ferroelectric-paraelectric phase transition temperature to lower temperatures with broadening dielectric peaks. Furthermore, an optimized recoverable energy density of 1.405 J/cm3 was achieved for BNT-0.10BMN ceramics under a low applied electric field of 140 kV/cm, which is mainly attributed to the transformation from ferroelectric to ergodic relaxor phase.

Structural Evolution and Enhanced Piezoelectric Activity in Novel Lead-Free BaTiO3-Ca(Sn1/2Zr1/2)O3 Solid Solutions

In this study, a series of solid solutions of (1−x)BaTiO3-xCa(Sn1/2Zr1/2)O3 (abbreviated as (1−x)BT-xCSZ, x = 0.00–0.15) ceramics have been prepared by the conventional solid-state reaction method to search for high performance lead-free piezoelectric materials. The structural evolution, microstructure, and piezoelectric properties are investigated. X-ray diffraction (XRD) results indicate that the phase symmetry strongly depends on the CSZ content. A tetragonal phase is well-maintained in the compositions of 0 ≤ x ≤ 0.03, and coexistence of tetragonal and cubic phases is obtained in the range of x = 0.06–0.09, beyond which a pure cubic phase becomes stable. More importantly, a significantly enhanced piezoelectric coefficient of d33 = 388 ± 9 pC/N is attained in the composition of x = 0.06 in the MPB region, where a tetragonal ferroelectric phase and an ergodic relaxor phase with average cubic symmetry coexist. Based on the analysis of crystal structure and dielectric properties, a temperature-composition phase diagram consisting of four phase regions is established. This study indicates that the lead-free BT-CSZ binary system has great potential for use in electromechanical transducer applications.

Large electrostrictive coefficient with optimized Electro-Strain in BNT-based ceramics with ergodic state

Electric field-induced high strain with low hysteresis and large electrostrictive coefficient are necessary for high-precision displacement actuators. Many works focused on achieve large strain through electric field-induced nonergodic-ergodic phase transition, while the accompanied large hysteresis hinders their practical application. Here, (1-x)(Bi0.54Na0.46)0.94Ba0.06TiO3-xSrTiO3 (BNBT-xST, x = 0.1, 0.2, 0.3, 0.4 and 0.5) ceramics are fabricated by a conventional solid state reaction method. The ergodic relaxor phase in BNBT ceramics was effectively regulated by doping SrTiO3. Finally, we achieve a high electro-strain of 0.17% with ultra-low hysteresis of 7.2% (@70 kV/cm) for × = 0.3 ceramics, and a large electrostrictive coefficient Q33 of 0.0251 m4/C2 (@70 kV/cm) with low strain hysteresis of 8.3% for × = 0.4 ceramics. This work provides a method for optimizing the strain-hysteresis trade-off and improving electrostrictive coefficient Q33 of BNT-based ceramics.

Composition dependent phase structure, dielectric and electrostrain properties in (Sr0.7Bi0.2□0.1)TiO3–PbTiO3–Bi(Mg0.5Ti0.5)O3 systems

Composition dependent transitions from normal ferroelectrics to nonergodic and finally to ergodic relaxor phase are observed in 0.7(Sr0.7Bi0.2□0.1)TiO3–(0.3 − x)PbTiO3–xBi(Mg0.5Ti0.5)O3 system (SBT–PT–xBMT, □ represents A–site vacancy). Rietveld refinement results show that with increasing BMT content, the system experiences a gradual transition from coexistence of pseudocubic and tetragonal (P c + T) to P c phase. The ferroelectric–relaxor phase transition and freezing temperature gradually decreases with addition of BMT content accompanied by an enhanced relaxor degree, which produces local disorder and polar nanodomains. This is also verified by Raman spectra and piezoelectric force microscopic analysis. The P–E loops transform from square to slant and finally to slim shape with increasing BMT component and an electric field-induced strain of ∼0.21% with ultralow hysteresis of ∼3.7% is obtained for x = 0.04 composition. The underlying mechanism for the large strain with low hysteresis lies in the existence of nonergodic and ergodic relaxor phase boundary and polar nanodomains at room temperature. Additionally, the multiphase coexistence contributes to a flatten free energy profile and thus contributing to such superior performances, as explained by a modified phenomenological model. High electrostrain with ultralow hysteresis in SBT–PT–xBMT systems are promising candidates in high–precision actuator applications.

Improved electric-field-induced strain and strong photoluminescence properties in novel Er3+-modified 0.93Bi0.5Na0.5TiO3-0.07BaTiO3 multifunctional ceramics

Recently, the progress of electronic devices toward miniaturization has strongly promoted development of multifunctional materials possessing multiple desirable properties. In this study, we develop and fabricate 0.93Bi0.5Na0.5TiO3-0.07BaTiO3-xEr multifunctional ceramics which show simultaneously considerable electric-field-induced strain and bright green light emission properties. With the introduction of Er3+, the ceramics gradually transform from non-ergodic relaxor phase to ergodic relaxor phase which could reversibly transform to ferroelectric phase under the electric field. As a result, with improving Er3+ content, the shape of the polarization-electric field loops of the ceramics become pinched, and it is obvious that the negative strain disappears while the positive strain gradually increases and reaches a maximum value 0.46% at x = 1.2 mol%. Besides, After the ceramics are poled, the light emission peak are greatly enhanced attributed to the decreased crystal symmetry and increased domain size, and is the strongest at x = 1.2 mol%. These results indicate that 0.93Bi0.5Na0.5TiO3-0.07BaTiO3-xEr ceramics are good candidates for developing multifunctional optoelectronic devices.

Crystal Structure, Electrical Properties, and Energy Storage Capacity of STCN Modified BNT-BKT Based Lead-Free Dielectrics

Perovskite solid solutions of SrTi(Cu1/3Nb2/3)O3 (STCN) modified 0.8Bi0.5Na0.5TiO3−0.2Bi0.5K0.5TiO3 (BNT-BKT) in the vicinity of morphotropic phase boundary composition were prepared. The dielectric and impedance properties associated with their structural evolution were investigated. Strong unsteadiness and large hysteresis (dielectric loss) under elevated temperature and variational frequency restrict the development of BNT-BKT based ceramics. Here we show a distinct phase transition from ferroelectric to ergodic relaxor phase that occurs with increasing STCN. Incremental chemical defects resulted from the substitution of the A/B site facilitate the distributions of polar nanoregions. The flatter and smoother dielectric curves between T s and T m illustrate good temperature stability. The complex impedance spectrums demonstrate that the compositions possess a mixed electronic and ionic conduction mechanism. More oxygen vacancies can be introduced into the lattice, contributing to a decremental impedance as the increased dopant. Meanwhile, will suppress p-type conduction and reduce dielectric loss. Favorable stabilities of dielectric permittivity, energy storage, and electrostrictive strain were achieved, attributed to the existence of nanodomains.

Enhanced electric field-induced strain and electrostrictive response of lead-free BaTiO3-modified Bi0.5(Na0.80K0.20)0.5TiO3 piezoelectric ceramics

ABSTRACT Lead-free (1-x)Bi0.5(Na0.80K0.20)0.5TiO3-xBaTiO3 or (1-x)BNKT-xBT (x = 0 – 0.15 mol fraction) piezoelectric ceramics have been investigated. The optimum density was found for the ceramic sintered at 1125°C, corresponding 98 – 99% of their theoretical values. All ceramics had a single perovskite structure. The coexisting mixed tetragonal-rhombohedral phases all over the entire compositional range with tetragonal phase becoming superior at higher BT. The diffuse phase transition was promoted by the addition of BT. With increasing BT content, the Tm and Td values were found to decrease. Phase transition from ferroelectric (FE) phase to ergodic relaxor (ER) phase was also induced by the changes in BT content. These changes significantly suspended long-range ferroelectric order, then correspondingly reducing the Pr and Ec , resulting in an improvement of electrostrictive and electric field-induced strain responses. A significant increasing of electric field-induced strain response (Smax = 0.37% and d*33 = 630 pm/V) is noted for the x = 0.05 ceramic. Furthermore, high electrostrictive coefficient (Q33 ) of 0.0421 m4/C2 is observed for this composition, which was more than ~ 2 times (~108%) as compared to the pure BNKT ceramic. The studied results indicated these ceramics can be considered promising candidates for actuator applications.

Comparing the electromechanical properties of CaTiO3‐ and BaZrO3‐modified Bi0.5Na0.5TiO3–SrTiO3 ceramics

The effects of CaTiO3 (CT) and BaZrO3 (BZ) modification upon the crystal structure and electromechanical properties of lead‐free Bi0.5Na0.5TiO3–SrTiO3 piezoelectric ceramics were compared within a doping range of 0–4 mol%. The different effects of CT and BZ modification upon the phase transition are clearly observed in the polarization and strain hysteresis loops. The CT‐modified specimens maintain strong ferroelectricity without any abnormal enhancement in the electric field‐induced strain. However, the addition of as little as 1 mol% BZ induces a transition from a nonergodic relaxor phase to an ergodic relaxor phase, thus resulting in disruption of the ferroelectric order and the generation of a high field‐induced strain. The present authors believe that the substitution of large ions (such as Zr4+) into the B‐sites, rather than the A‐sites, of the Bi0.5Na0.5TiO3‐based ceramics plays a significant role in the phase transition behavior.

The Effect of Cu2+ Substitution on the Properties of BNKLT Lead-Free Ceramics Fabricated by the Solid-State Combustion Technique

This article reports the effect of Cu2+ substitution on the phase formation, morphology and electrical behavior of Bi0.5Na0.34K0.11Li0.05Ti(1-x)CuxO3 with 0 ≤ x ≤ 0.020 (BNKLT-xCu) ceramics prepared by the solid state combustion technique with glycine used as the fuel. All samples were prepared with a calcination temperature and a sintering temperature of 750 °C and 1025 °C, respectively for 2 h. The XRD results of all compositions revealed a single perovskite structure and that Cu2+ diffused efficiently into B-sites of the lattice, producing a BNKLT-xCu solid solution. The phase formation of the BNKLT-xCu ceramics showed coexisting rhombohedral (R) and tetragonal (T) phases in all samples. The highest measured density of the BNKLT ceramics was 5.99 g/cm3 and good dielectric properties measured at the temperature of the maximum dielectric constant (ε m = 4723 and tanδ = 0.054), were obtained by the sample with Cu2+ substituted at x = 0.010. The BNKLT-xCu ceramics with Cu2+ ≥ 0.005 showed pinched P-E loops, and the negative strain of the S-E loops started to disappear, owing to the Cu2+ induced transformation from the ferroelectric (FE) phase to the ergodic relaxor (ER) phase. With Cu2+ levels of 0.010, the d*33 value increased to 705 pm/V, indicating that this sample was near the FE–ER phase boundary with induced high strain. Substituting an appropriate amount of Cu2+ improved the densification of BNKLT-xCu ceramics as capillary forces in the liquid phase during sintering pulled the grains together, which increased the εm values.

Energy storage density and piezoelectric performances of barium strontium titanate modified bimuth sodium lanthanum titanate lead-free ceramics

Lead-free (1-x)(Bi0.487Na0.487La0.017)TiO3-x(Ba0.7Sr0.3)TiO3 or (1-x)BNLT-xBSrT ceramics were fabricated by a solid state reaction and sintered at 1050–1200 °C for 2 h. All sintered samples had a relative density > 97% of their theoretical values. With increasing BSrT, the transition from BNLT rhombohedral to BSrT tetragonal was observed. The addition of BSrT inhibited grain growth which resulted in the improvement of the densification of the BNLT ceramic. The changes in the BSrT content also induced a phase transition from the ferroelectric (FE) phase to the ergodic relaxor (ER) phase. These changes significantly disrupted long-range ferroelectric order, thereby correspondingly reducing the Pr and Ec values and resulting in the enhancement of the electric field-induced strain and electrostrictive response. A large Smax = 0.41%, d*33 = 788 pm/V and electrostrictive coefficient (Q33 = 0.04119 m4/C2) were observed for the x = 0.08 sample. In addition, the x = 0.15 sample showed good energy storage density (W = 0.66 J/cm3) and energy storage efficiency (η = 82.7%) @ 150 °C. Overall, these results indicated that these ceramics had the potential of becoming one of the promising lead-free piezoelectric candidates for piezoelectric applications.