Perovskite Ceramics Research Articles

Research Progress of Ba(Zn1/3Nb2/3)O3 Microwave Dielectric Ceramics: A Review

Ba(Zn1/3Nb2/3)O3 (BZN) microwave dielectric ceramics have attracted great attention due to their high-quality factor (Q), near-zero temperature coefficient of resonant frequency (τf), and suitable dielectric constant (εr), making them promising materials for application in microwave devices. Due to their superior dielectric properties, composite perovskite ceramics are widely used in the field of microwave communication, base stations, navigation, radar, etc. This article summarized the latest research progress of BZN ceramics and discusses the main preparation methods and performance modifications. Furthermore, the problems faced by BZN ceramics and solutions to improve their performance, as well as their potential applications, are analyzed. This article provides a reference for the design and preparation of BZN ceramics.

The effects of double-site yttria-doping on the structures and dielectric properties of (Ca,Sr)z(Zr,Ti)O3−δ perovskite ceramics

Double-site yttria-doped (Ca,Sr)z(Zr,Ti)O3−δ (CSZTY) ceramics were synthesized using the solid-state reaction method.

Processing and electrical conductivity property of lithium-doped high-entropy pyrochlore and perovskite ceramics

Lithium-doped Li0.66La1.12(Ti0.2Zr0.2Hf0.2Sn0.2Nb0.2)2O7 (LLTNO), Li0.66La1.12(Ti0.2Zr0.2Hf0.2Sn0.2Ta0.2)2O7 (LLTTO) high-entropy pyrochlore and Li0.5Sr0.5(Ti0.2Zr0.2Hf0.2Sn0.2Ta0.2)O3 (LSTTO), Li0.5Ba0.5(Ti0.2Zr0.2Hf0.2Sn0.2Nb0.2)O3 (LBTNO) high-entropy perovskite ceramics were synthesized by solid state reaction method and sintered. Crystal structure, microstructure and electrical properties of these high entropy ceramics were studied. The LLTNO and LLTTO pellets sintered at 1300 ?C present a pyrochlore structure, while LSTTO and LBTNO pellets sintered at 1350 ?C present a perovskite structure. The LBTNO ceramics has a total conductivity of 1.25 ? 10?7 S?cm?1 at room temperature while the LSTTO sample exhibits the highest conductivity of 2.11 ? 10?7 S?cm?1 among all samples. Both LSTTO and LBTNO ceramics present negligible electronic conductivity. Relative densities of the LLTNO, LLTTO, LSTTO and LBTNO ceramics were 82, 88, 86 and 87%TD, respectively, which is the reason for low conductivity of these high entropy ceramics. The activation energies of the LSTTO and LBTNO samples were 0.39 and 0.38 eV, respectively, which is close to the traditional Li+-type conducting solid electrolytes.

Magneto-dielectric properties of B-site doped (Fe3+, Zr4+) BiMnO3 perovskite ceramic

A Zirconium (Zr4+) and Iron (Fe3+) doped perovskite compound i.e., BiMn1-x(TE)xO3 (x = 0.0, 0.1 and TE = Fe, Zr) were successfully prepared by mechanical alloying route. The X-ray diffraction pattern and HRTEM confirms the formation of single-phase perovskite in the proposed compositions. The lattice parameters were found to be reduced with Fe3+ and increased for Zr4+ ions entering in the crystal structure by substitution of Mn3+ ion. Scanning Electron micrographs (SEM) depicted the grain refinement of the oxidex. The XPS analysis exhibited the isovalent (Fe3+) and tetravalent (Zr4+) status of doping on the B-site Their effect on the oxygen vacancies, and the reduction of Mn3+ ions are reported. The dielectric study at 100 Hz and 400 °C(max.) indicate the decrement in dielectric constant to 12.76 × 103 in Fe+3 doped ceramic and 10.68 × 103 in the case of Zr+4 doped ceramic concerning that of 13.02 × 103 in pristine ceramic. M−H loop study exhibited ferromagnetic characteristics in doped and pristine ceramics. The Ms measured as 0.135emu, 0.114emu and 0.096emu in Fe doped, Zr doped and pristine ceramics respectively. The coexistence of magnetic and dielectricity exhibited the justified modifications of manganates perovskite ceramics and competently met the challenge of replacing conventional materials.

VecMap: A Python-based Graphic User Interface Tool for Atomic Displacement Mapping in Perovskite Structures.

VecMap, a python-based graphic user interface tool was developed to help analyzing the atomic displacements in perovskite ceramics. With an input of a high-resolution STEM image in which the A-site, B-site, and/or O columns clearly resolved, VecMap outputs the displacement vector maps of either A-site or B-site cations, as well as the oxygen vector map if O columns are visible, in a highly automated fashion. A "Coupled HAADF-ABF" function was specially designed for easy atom finding in ABF images, in case the A-site and B-site atoms are too close in atomic numbers to show enough contrast. VecMap greatly simplifies the analysis of atomic displacement in perovskite structures.

Effect of MnO on the Dielectric Properties of Nb-SrTiO3 Ceramics for Capacitor Applications

Nb-SrTiO3 perovskite ceramics, without and with the addition of 3 mol % MnO, were synthesized by an organic gel-assisted process, sintered under argon/hydrogen, and annealed under oxygen. For both series, colossal permittivity (>104), low loss tangent (<0.1), and high resistivity (109 Ω cm) at 1 kHz were obtained. Furthermore, the dielectric measurements exhibit good frequency stability regardless of the grain size of the ceramics. Indeed, the Nb-SrTiO3 samples show a small grain size (2 μm), and the addition of MnO leads to a strong increase in grain size up to about 40 μm. The mechanism responsible for the colossal permittivity and low dielectric loss is discussed on the basis of analyses of impedance spectroscopy and EPR data. EPR measurements reveal the existence of oxygen vacancies and different oxidation states of Mn in the grains. The grain boundaries and grains resistance were deduced from a fit of an RC element model to the impedance spectroscopy data. From all of these results, it was shown that the grains are semiconducting and the grain boundaries are insulating. The correlation between permittivity as a function of grain size and grain boundary capacity validates the barrier layer model between the grains and grain boundaries. Thus, the electrical behavior of the grain boundaries is one of the key factors to obtain ceramic capacitors useful for industrial applications.

Effects of Ca3Co4O9 addition on physical and electrical properties of lead-free Bi0.5(Na0.80K0.20)0.5TiO3-0.005LiNbO3 ceramic

In the present work, highly dense complex perovskite oxide ceramics with the formula of (1-x)[Bi0.5(Na0.80K0.20)0.5TiO3-0.005LiNbO3]-x(Ca3Co4O9) or (1-x)[BNKT-0.005LN]-xCCO, where x = 0, 0.010, 0.015, 0.020 and 0.025 mol fraction were fabricated by a solid-state mixed oxide method. After sintering at 1125 °C for 2 h, all ceramics were characterized in terms of physical, phase evolution, microstructure, dielectric, ferroelectric, and piezoelectric properties. XRD patterns of all samples indicated single phase of perovskite structure with good relative density value of ∼ 97 − 98%. The SEM image indicated that cubic-like shaped grains were observed in all samples. The average grain size was found to increase with increasing the modifier content. Optimum electrical properties (i.e. εr = 1485, tanδ = 0.0460, Pr = 13.13 µC/cm2, Ec =14.92 kV/cm and d33 = 145 pC/N) were found in the sample with x = 0.010 mol fraction.

Improved microwave dielectric characteristics in CaHf1−xTixO3 ceramics

AbstractIn the present work, effects of Ti‐substitution for Hf upon microwave dielectric characteristics for CaHfO3 ceramics were investigated. CaHf1−xTixO3 solid solution in space group Pnma was determined in the present ceramics with x = 0–0.075, and only minor amount of secondary phases of CaHfO3 (R, 1.3 wt%) and Ca2Hf7O16 (R, 0.8 wt%) was detected. The significantly improved microwave dielectric characteristics were achieved with Ti‐substitution in CaHfO3 ceramics. With increasing x, the temperature coefficient of resonant frequency τf was substantially tuned from negative to positive through zero, which was caused by the decrease of oxygen octahedral tilting, and the Qf value was apparently improved simultaneously and reached the maximum of 43670 GHz at x = 0.025, while the dielectric constant εr increased monotonously. The remarkable improvement of Qf was attributed to the enhancement of octahedral framework rigidity and the decreased nonuniform distribution of inner chemical bonding in crystal based on the change of chemical bond parameters calculated by the Phillips–Van Vechten–Levine bond theory, which was further confirmed by the higher frequency and narrower width of stretch mode of octahedron (i.e., A1g(O) near 730 cm−1) in Raman spectra. An interesting phenomenon was found in titanium‐containing perovskite ceramics that they had consistent trend of τf changing with tolerance factor, which was helpful to design temperature‐stable perovskite microwave dielectric ceramics. The best combination of microwave dielectric characteristics was achieved at x = 0.035: εr = 27.2, Qf = 42 870, and τf = +3 ppm/°C. For practical applications of the present ceramics, further improvement of Qf is required, and it is expected to be achieved through microstructure optimization.

Exaggerated grain growth and the development of coarse-grained microstructures in lithium lanthanum titanate perovskite ceramics

Li3xLa2/3−x⎕1/3–2xTiO3 (LLTO) ceramics is recognized as one of the most promising solid electrolytes for applications in all-solid-state batteries. The total ionic conductivity is usually diminished by the contribution of grain boundaries, therefore microstructures with larger grain sizes are desirable. In this work we prepared compositions with slightly decreased TiO2 additions, i.e. increased La:Ti ratio, and triggered the formation of Ruddlesden-Popper type sequences with structural elements of the Li2La2Ti3O10 phase within the matrix perovskite LLTO grains as revealed by HAADF-STEM. These grains exhibit exaggerated grain growth (EGG), which initially results in the development of bimodal microstructures. At higher sintering temperatures, grain growth continues by enhanced coarsening via Ostwald ripening and the RP-type sequences recrystallize to perovskite LLTO. This results in the development of dense microstructures with LLTO grains measuring up to 100 µm in diameter. The findings represent a novel and straightforward approach for the preparation of coarse-grained LLTO ceramics.

Colossal dielectric properties of Li- and Sm- based perovskite ceramics: A combination of first-principles calculations and experiments

The Li1/2Sm1/2Cu3Ti4O12 ceramic, which is in the ACu3Ti4O12 class, was investigated by means of both experimental and theoretical approaches. In our experiments, it was made via a solid-state reaction. Our XRD measurements revealed that the crystal structure of this sintered ceramic possesses a body-centered cubic system with an Im3 space group. Moreover, CuO and Sm4Ti3O12 impurity phases were observed. At 1 kHz and 20 °C, a high dielectric constant of approximately 3615–3838 and a rather low loss tangent of 0.119–0.185 were achieved for Li1/2Sm1/2Cu3Ti4O12 ceramics. According to our density functional theory calculations, we found that Li and Sm ions preferably occupy Cu and Ca sites, respectively. From our electron density analysis, there is a charge transfer from Li to Sm in this ceramic, although the valence states of Cu and Ti are constant. Cu+ and Ti3+ ions were detected by incorporating an oxygen vacancy into this structure. Based on our results, an internal barrier layer capacitor is a significant contributor to the enormous dielectric characteristics of this ceramic.

Influence of Sintering Parameters on Spectroscopic Properties of BMW: Eu3+ Ceramic Materials Prepared by HPLT Technique.

In this work, Ba2MgWO6: Eu3+ (BMW: Eu3+) ceramic materials with a double perovskite structure were sintered using the High-Pressure Low-Temperature sintering (HPLT) technique. As part of the research, the influence of pressure (CP), sintering temperature (CT), and sintering time (CTS) on the structure and luminescence of the doped BMW were determined. Structural analysis via XRD and SEM + EDS and spectroscopic analysis via emission and excitation spectra, decay time, and absorption spectra of the obtained ceramics were performed. Dense double perovskite ceramics were obtained with a cubic structure with optimal sintering parameters: T = 500 °C, p = 8 GPa, and t = 1 min. The increase in temperature caused an increased extinction of the luminescence due to the diffusion of carbon into the ceramics. The increase in pressure led to the formation of the amorphous phase, which increased the speed of non-radiative transitions and also led to the extinction of the luminescence. The increase in sintering time from 1 to 3 min enhanced the luminescence output, but when the ceramic was sintered for 5 min, the luminescence was quenched, most likely by increasing the rate of the non-radiative process, as evidenced by reduced decay time.

Fabrication of a lead-free ternary ceramic system for high energy storage applications in dielectric capacitors.

The importance of electroceramics is well-recognized in applications of high energy storage density of dielectric ceramic capacitors. Despite the excellent properties, lead-free alternatives are highly desirous owing to their environmental friendliness for energy storage applications. Herein, we provide a facile synthesis of lead-free ferroelectric ceramic perovskite material demonstrating enhanced energy storage density. The ceramic material with a series of composition (1-z) (0.94Na0.5Bi0.5TiO3-0.06BaTiO3)-zNd0.33NbO3, denoted as NBT-BT-zNN, where, z = 0.00, 0.02, 0.04, 0.06, and 0.08 are synthesized by the conventional solid-state mix oxide route. Microphases, microstructures, and energy storage characteristics of the as-synthesized ceramic compositions were determined by advanced ceramic techniques. Powder X-ray diffraction analysis reveals pure single perovskite phases for z = 0 and 0.02, and secondary phases of Bi2Ti2O7 appeared for z = 0.04 and 0.08. Furthermore, scanning electron microscopy analysis demonstrates packed-shaped microstructures with a reduced grain size for these ceramic compositions. The coercive field (Ec) and remnant polarization (Pr) deduced from polarization vs. electric field hysteresis loops determined using an LCR meter demonstrate decreasing trends with the increasing z content for each composition. Consequently, the maximum energy storage density of 3.2J/cm3, the recoverable stored energy of 2.01J/cm3, and the efficiency of 62.5% were obtained for the z content of 2mol% at an applied electric field of 250kV/cm. This work demonstrates important development in ceramic perovskite for high power energy storage density and efficiency in dielectric capacitors in high-temperature environments. The aforementioned method makes it feasible to modify a binary ceramic composition into a ternary system with highly enhanced energy storage characteristics by incorporating rare earth metals with transition metal oxides in appropriate proportions.

Synthesis and densification of BaZrO3 ceramics by reactive cold sintering of Ba(OH)2⋅8H2O-Zr(OH)4 powders

Reactive cold sintering (RCS) is a combination of a low-temperature reaction and the cold sintering process, and it is used for the direct synthesis and simultaneous consolidation of ceramic powders. Here, we investigated RCS of BaZrO3 through the reaction between Ba(OH)2⋅8H2O and Zr(OH)4, and obtained pure BaZrO3 compacts with a relative density of ∼92% under the conditions of Zr(OH)4 ball-milling for 30 min, Ba/Zr ratio of 1.15, and holding a temperature of 350 °C for 60 min. The effects of processing parameters on the phase structure, relative density, microstructure evolution, and dielectric property of the BaZrO3 bulk were studied in detail. The results suggest that the synthesis and densification of BaZrO3 bulk in the RCS process involved the steps of dissolution, reaction, agglomeration, collapse, and densification. The present study extends the applicability of RCS to the preparation of high-density perovskite ceramics with nanograins.

Relaxor ferroelectric behaviour observed in (Ca0.5Sr0.5Ba0.5Pb0.5)Nb2O7 perovskite layered structure ceramics

Relaxor ferroelectric behaviour was observed in perovskite layered structure (PLS) (Ca0.5Sr0.5Ba0.5Pb0.5)Nb2O7 (CSBPN) ceramics engineered using the high entropy approach. The CSBPN ceramics were sintered at 1350 °C and are single-phase with an orthorhombic structure (Cmcm space group) at room temperature. Their relaxor ferroelectric behaviour is characterized by a broad and frequency-dependent permittivity maximum and a current peak around zero electric field in the hysteresis loop. The presence of polar nanoregions is supported by piezoresponse force microscopy images. The value of the relative permittivity ɛ′ = 130 at 1 kHz and room temperature is much larger than that for conventional PLS ceramics Sr2Nb2O7 (ɛ′ = 42) and Ca2Nb2O7 (ɛ′ = 38). This can be attributed to the presence of polar nanoregions and the lattice distortion effect in high entropy materials. The appealing dielectric and relaxor behaviour of CSBPN ceramics confirms the efficacy of the high entropy approach to obtain improved properties.

Design of superior electrostriction in BaTiO3‐based lead‐free relaxors via the formation of polarization nanoclusters

AbstractElectrostrictive materials have wide applications in modern high‐precision electronic devices. Driven by growing environmental concerns, there is demand for lead‐free materials with superior electrostriction behaviors. In this study, we demonstrate a record‐high electrostrictive coefficient of ~0.0712 m4 C−2 in perovskite ferroelectric ceramics, along with hysteresis‐free strain as well as excellent frequency and thermal stabilities, in lead‐free BaTiO3‐based ceramics through a polarization nanocluster design. By appropriately introducing Li+ and Bi3+ into the BaTiO3 lattice matrix, the long‐range ferroelectric ordering can be broken, and polarization nanoclusters can be formed, resulting in a relaxor state with concurrently suppressed polarization and maintained electro‐strain. A three‐dimensional atomic model constructed using advanced neutron total‐scattering data combined with the reverse Monte Carlo method indicates the existence of Bi and Li segregations at the subnanometer scale, which confirms the prediction made by density functional theory calculations. Such a short‐range chemical order destroys the long‐range ferroelectric order of the off‐centered Ti polar displacements and leads to the embedding of Li+/Bi3+‐rich polar nanoregions in the Ba2+‐rich polarization disorder matrix. Further, a completely reversible electric‐field‐induced lattice strain is observed, giving rise to pure electrostriction without hysteresis behavior. This work provides a novel strategy for developing lead‐free relaxor ferroelectrics with high electrostriction performance.image

Effects of yttrium doping on structural, electrical and optical properties of barium titanate ceramics

In this report, we study the Yttrium-doped Barium Titanate (Y-BT) Ba1 − xYxTiO3 (with x = 0.00, 0.01, 0.03, 0.05, 0.07 mmol) perovskite ceramics synthesized by sol-gel method. The as-made powder samples were pressed into a pellet shape and subsequently sintered at 1300 °C for 5 h in air. The structural, morphological, electrical, and optical properties of the synthesized samples were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), impedance analyzer, and UV-Vis-NIR Spectroscopy respectively. The XRD study revealed the formations of single phase tetragonal structure of Barium Titanate (BT) with ∼23–33 nm mean crystallite size. The crystallite size increases initially with Y-doping, found at about 33 nm for x = 0.01, and reduces for increase in Y3+ concentration further. The microstructural study from FESEM depicts the uniform distribution of compact and well-faceted grain growth for Y-BT in contrast with undoped barium titanate. The average grain size (∼0.29–0.78 μm) of the Y-BT decreases with increasing doping concentration. Frequency-dependent impedance analyses show enhanced dielectric properties like dielectric constant, quality factor, and conductivity with low dielectric loss in the presence of Yttrium. The optical bandgap energy (∼2.63–3.72 eV) estimated from UV-Vis-NIR diffuse reflection data shows an increasing trend with a higher concentration of yttrium doping.

Dielectric and energy storage properties of (La,Li) [(Bi,Na)BaSrCa]1-TiO3 high-entropy perovskite ceramics

A series of single-phase (La 0.5 Li 0.5 ) x [(Bi 0.5 Na 0.5 ) 0.25 Ba 0.25 Sr 0.25 Ca 0.25 ] 1- x TiO 3 high-entropy perovskite ceramics were designed and successfully synthesized via conventional solid state reaction method. The results of dielectric properties indicate that all samples in different proportions exhibit excellent frequency stability at a wide frequency range (10 2 –10 6 Hz) and quintessential relaxation phenomenon. An optimal dielectric constant ( ε r = 920) with low dielectric loss (tanδ = 0.015) was achieved for x = 0.20, which is represented as equimolar high-entropy ceramic. It can be demonstrated that an amazing energy storage efficiency of 95.3% and a discharge density of 1.23 × 10 −2 J/cm 3 can be simultaneously achieved in x = 0.24 ceramics. Furthermore, it is confirmed by X-ray photoelectron spectroscopy that the charge compensation mechanism and the oxygen vacancies synergistically cause more Ti 4+ to be reduced, which rationalizes the elevated dielectric properties. We believe that entropy engineering is a credible strategy for tailoring material properties.

Improvement of electrical and magnetic properties in La0.67Ca0.33Mn0.97Co0.03O3 ceramic by Ag doping

For the perovskite manganite La1-xCaxMnO3, achieving high temperature coefficient of resistance (TCR) and magnetoresistance (MR) is the key to realize its potential applications. In this study, high-quality La0.67Ca0.33Mn0.97Co0.03O3:Agx polycrystalline ceramics were prepared by the sol-gel method. The results show that Ag doping has important impact on metal-insulator and ferromagnetic-paramagnetic transitions. A Ag doping amount increases, the grain size of the samples increases at x = 0.05 and then decreases. The doping of Ag can improve the crystalline quality of the samples and enhance the connectivity between grains, thereby improving the metallicity of the system. Additionally, with Ag doping amount increases, the resistivity of the samples gradually decreased, while the Curie temperature and the metal-insulator transition temperature gradually increased. Especially after Ag doping, both the TCR peak (TCRpeak) and the MR peak (MRpeak) values are significantly improved. The TCRpeak reaches 65.2%·K−1 at x = 0.1, while the MRpeak is as high as 82.6% at x = 0.05 under 1 T magnetic field. Doping perovskite manganite ceramics with Co and Ag can greatly optimize their TCR and MR, favoring the potential applications of these materials.

Large piezoelectricity in BiScO3-PbTiO3 based perovskite ceramics for high-temperature energy harvesting

Advanced high-temperature piezoceramic energy harvesters (HT-PEHs) highly rely on perovskite ceramics with large high-temperature piezoelectricity. However, it remains a great challenge to achieve high piezoelectric coefficient (d33) at elevated temperatures, which severely limits the development of piezoelectric materials in cutting-edge energy harvesting applications. Here, yBiScO3-xPbTiO3-0.05Pb(Zn1/3Nb2/3)O3 (yBS-xPT-PZN) ternary perovskite piezoceramics are prepared, in which the morphotropic phase boundary (MPB) composition (x/y = 0.60/0.35) exhibits a large d33 of 655 pC/N at 300 °C, outperforming many reported other perovskite piezoceramics. The excellent high-temperature piezoelectricity should benefit from the lattice softening effect and the stable ferroelectric domain state associated with the high tetragonal phase content. In addition, the HT-PEH assembled from the MPB sample exhibits good power generation performance (e.g., a giant power density of 418 μW/cm3) at 300 °C, and can charge a 10 μF commercial capacitor to 7 V within 40 s. Such a large piezoelectric coefficient and power density of yBS-xPT-PZN system at a high temperature of 300 °C is a promising candidate for fabricating high-performance HT-PEHs to meet the urgent requirements of advanced high-temperature energy harvesting applications.

Rainer Waser – A Pioneer of Fundamentals of Resistive Switching Memories

Rainer Waser – A Pioneer of Fundamentals of Resistive Switching Memories