BaZrO3 Ceramics Research Articles

Machine learning optimization for a novel process of acid-base chemical densification of BaZrO3 ceramics

Low-temperature ceramic fabrication techniques, which can reduce CO2 emissions and energy consumption, are important. BaZrO3 ceramics, which are conventionally sintered at over 1600 °C, were prepared at close to room temperature by a novel process called acid-base chemical densification (ABCD). BaZrO3 ceramics could be fabricated by reacting a compact of ZrO2 hydrous gel with a solution of Ba(OH)2·8H2O at less than 100 °C. The densities of BaZrO3 ceramics depended on the various ABCD process parameters. To obtain a higher density of BaZrO3 ceramics, all the parameters were optimized simultaneously using machine learning. Three algorithms, Linear Regressor (LR), Random Forest (RF) regressor, and Light Gradient Boost Machine (LGBM), were compared for the prediction of BaZrO3 density. The RF regressor predicted the relative densities of BaZrO3 ceramics using the process parameters with high accuracy. From the results of the important features obtained from the RF model, the water content in the zirconia hydrous gel used as a precursor is important for the densification of BaZrO3 in this process, although the reaction time and precursor density affected the densities in the ABCD process. In contrast, varying the reaction temperature in the chemical reaction between ZrO2 hydrous gel and Ba(OH)2·8H2O did not effectively improve the density in this study. By analyzing the top six important features in the RF model, we attempted to improve the accuracy of density prediction using the LR to predict the densities from the extrapolation data. Using an improved LR model, it was found that reducing the water content in the precursors is important for obtaining dense BaZrO3 ceramics by the ABCD process. The water in the gel disturbs the densification because the volume of water molecules remains as pores in the pellets.

Preparation, Structure, and Dielectric and Nonlinear Optical Properties of (K0.5Na0.5)NbO3–BaZrO3 Ceramics

Preparation, Structure, and Dielectric and Nonlinear Optical Properties of (K0.5Na0.5)NbO3–BaZrO3 Ceramics

Effect of Sr2+doping on the microwave dielectric properties of BaZrO3 ceramics

ABSTRACT In this study, undoped and Sr2+ doped BaZrO3 ceramics were prepared by solid-state reaction using 3 wt-% B2O3 as sintering aid. The phase composition and microstructure of BaZrO3 were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that introducing an appropriate amount of Sr2+ makes BaZrO3 ceramics Q × f value and density increase. In addition, the dielectric constant of BaZrO3 ceramics increases with the increase of Sr2+ addition. With excellent microwave dielectric properties, ϵ r = 34.17 and Q × f value of 39,070 GHz(@ 7.8 GHz) τf = + 140 ppm/°C were obtained in 6 at.-% Sr2+ doped BaZrO3 with 3 wt-% B2O3 sintering aid at 1275°C for 5 h. Using this material as the medium, the simulation of GPS antenna by HFSS software shows that this material has the potential to be used as the antenna medium material.

Effect of Sintering Conditions on the Electrical Properties of Lead-Free Piezoelectric Potassium Sodium Niobate-Based Ceramics

Lead-free piezoelectric 0.92(K0.445Na0.5Li0.05)NbO3-0.08BaZrO3 (KNLN-BZ) ceramics were prepared via conventional sintering. Single-step, 2-step and 3-step temperature-controlled conditions were designed. The structure and electrical properties of ceramics obtained using different temperature-controlled procedures were systematically studied. It was found that ceramic prepared using the 3-step method with a holding time of 20 h showed the highest electrical properties. The Curie temperature was approximately 286 °C, and the dielectric constant and dielectric loss at room temperature were 1350 and 4.5% at the frequency of 1 kHz, respectively. The highest remanent polarization, piezoelectric strain and piezoelectric coefficient, d33*, were obtained 60 °C, indicating a phase transition between ferroelectric phases. Although the ceramics did not show excellent piezoelectric properties, the 3-step sintering method can be considered an effective method to optimize the electrical performances of KNN-based ceramics. Combined with an appropriate composition, ceramics with excellent electrical properties could be obtained. This study provides a path to enhance the density and electrical properties for KNN-based ceramics with simple composition and potential for industry application.

Texture performance of lead-free Bi1/2Na1/2TiO3–BaZrO3 ceramics

The effect of Bi1/2Na1/2TiO3 (BNT) template on texture development of 0.94Bi1/2Na1/2TiO3-0.06BaZrO3 (BNT-BZ) ceramics was investigated. Employing plate-like BNT templates, textured BNT–BZ ceramics were developed through conventional solid-state reaction (CSSR) and reactive-templated grain growth following a tape-casting process. Structural results show that all compositions crystallized into simple perovskite phase. Introduction of BNT templates into BNT-BZ ceramics stabilized the ferroelectric state and enhance dielectric constant, field-induced strain, and piezoelectric coefficient. Enhancement in electromechanical properties of the textured ceramics were more pronounced in comparison with conventionally processed BNT-BZ ceramics and their composite counterparts. Direct comparison of the BNT-BZ ceramics developed by CSSR with their textured counterparts showed that the dielectric constant (ε) of textured samples increased 32%, piezoelectric constant (d33) 70% and field-induced strain (Smax) increased 141%. The results obtained from the structure and electromechanical properties confirm that texture engineering play an important role in improving the piezoelectric properties of ceramics.

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.

Characterization of Y and Mn co-substituted BaZrO3 ceramics: Material properties as a function of the substituent concentration

Innovations in materials science are the key element for solving technological challenges. Various energy and environmental applications require designing materials with tailored compositions, microstructures and specific target-oriented performance. Y and Mn co-substituted BaZrO3, e.g. BaZr0.85Y0.15Mn0.05O3-δ, has previously attracted attention as a membrane material for H2 separation from gas mixtures due to its mixed proton-electron conductivity leading to appreciable levels of H2-flux at elevated temperatures and its good thermo-chemical stability under reducing environments. In the present work, we developed ceramic materials within the BaZr0.8Y0.2-xMnxO3-δ series, where x = 0.02–0.15. The study of their functional properties in dependence of the Y-to-Mn ratio disclosed that thermal expansion and hydration decrease by increasing the Mn content as well as the total electrical conductivity. In addition to that, XPS analysis and near edge X-ray absorption fine structure spectra (NEXAFS) in the vicinity of O K-edge and Mn L2,3-edges indicated that the Mn atoms oxidation state in the surface and in the bulk range from Mn2+ to Mn4+ depending on the ambient conditions that can be encountered in MPEC electrodes, which it is suggested to be related with a hydration mechanism mediated by Mn oxidation and subsequent proton attachment to oxygen neighbors, similar to LSM.

Characterization of Y and Mn co-substituted BaZrO3 ceramics: Material properties as a function of the substituent concentration

Characterization of Y and Mn co-substituted BaZrO3 ceramics: Material properties as a function of the substituent concentration

Variation of citrate to metal cation ratio for dense and phase pure BaZrO3 via autocombustion synthesis

AbstractIn this work, we demonstrate how the metal–citrate complex structure formed in the gel reflects the true stoichiometry of the redox mixtures to yield a highly dense BaZrO3 ceramic obtained as a combustion product in the sol‐gel autocombustion technique. By systematically varying the citric acid to metal cation ratio (C/M) between 0.56, 1.0, 1.5, and 2, we show that the optimal synthesis parameters correspond to C/M ratio of 1.5, at which ratio complete chelation of citrates happen with nitrates. This was confirmed using TGA, which showed a single‐step weight loss peak corresponding to C/M =1.5 but multiple peaks in C/M ratios of 0.56 and 1. PXRD and FTIR measurements on all the burnt powders showed multiphase peaks for the C/M ratios 0.56 and 1 but only peaks corresponding to BaZrO3 for C/M = 1.5, apart from a very tiny BaCO peak. Combustion behavior of each sol‐gel corresponding to C/M ratios 0.56, 1.0, 1.5, and 2.0 is described in detail, wherein 0.56 and 1.0 sol‐gels were found to belong to the smouldering/less intense flame‐type combustion, while 1.5 and 2 belonged to the intense flame combustion, contradicting oxidant to reductant ratio (O/R) calculations that require a stoichiometric combustion for C/M ratio of 0.56 to result in an intense flame combustion. This discrepancy was explained by the optimal usage of NO ions in the gel structure corresponding to C/M ratio of 1.5 since a complete chelation of citrates to nitrates ions happen for C/M = 1.5. The observed combustion behavior, phase purity, and other characteristics of stoichiometric/ nonstoichiometric combustion products are illustrated by means of the extent of the 3D metal–citrate complex network formed as a function of C/M. The density of the sintered pellets that were sintered at a temperature of 1650C was found to be the best at 99.6 for the C/M ratio 1.5. This is the highest ever reported density for BaZrO3 ceramic demonstrating that C/M ratio of 1.5 represents that metal to cation ratio for which best chelation of citrates happen with nitrates resulting in the formation of dense BaZrO3 ceramics. A comparison of BaZrO pellet made by solid‐state synthesis technique yielded a low value of density of 97.5. Impedance spectroscopy measurements done on all BaZrO pellets yielded the lowest grain‐boundary resistance for the pellet made by the sol‐gel technique with C/M ratio of 1.5.

Investigation the effect of Sb on phase boundary variation of 0.965(Na0.5K0.5)(Nb1-x Sb x )-0.035BaZrO3 ceramics and the corresponding piezoelectric properties

ABSTRACT CuO-added 0.965(Na0.5K0.5)(Nb1-x Sb x )-0.035BaZrO3 ceramics (0.00 ≤ x ≤ 0.10) were well prepared at 1070°C for 8 hours. And the effect of Sb5+ ions on the phase boundary variation and the corresponding piezoelectric properties were studied. It was found that the crystal structures varied from orthorhombic-tetragonal, orthorhombic-tetragonal-rhombohedral, orthorhombic-rhombohedral PPB and finally to rhombohedral structures of 0.965(Na0.5K0.5)(Nb1-x Sb x )-0.035BaZrO3 with x value increasing, and the corresponding piezoelectric properties varied according to the variation of crystal structures. Particularly, the specimen with an Amm2 orthorhombic (11.1%) – R3m rhombohedral (88.9%) dominant PPB structure (x = 0.08) showed the highest d33 value of 415 pC/N and strain of 0.12% at 4.5 kV/mm.

Structural refinement, morphological and electrical properties of BaZrO3:Bi(Zn1/2Ti1/2)O3 lead-free ceramics

In this work, barium zirconate (BaZrO3) ceramics were synthesized by solid state reaction method together with bismuth zinc titanate [Bi(Zn1/2Ti1/2)O3] and sintered at 1200 °C for 5 h. These materials were characterized by X-ray diffraction (XRD), Rietveld refinement, Scanning spectroscopic measurements (SEM) and Impedance spectroscopy, in order to produce a novel material lead-free due to environmental concern. XRD measurements with the Rietveld refinement technique confirmed that BaZrO3 ceramics have a perovskite-type cubic structure for all different molar ratio studied. In the higher composition of BaZrO3, the perovskite phase symmetry was refined with a single cubic structural based on BaZrO3 code ICSD-27048. For other compositions it was possible to add a second structure regarding the BaO cubic element, which seems to be a remnant phase in the matrices. Impedance Spectroscopy (IS) measurements revealed that BaZrO3:Bi(Zn1/2Ti1/2)O3 content increased the materials’ conductivity. Two conduction mechanisms occur on the matrices: grain and grain boundaries regarding high and low frequencies, respectively. SEM was carried out and confirmed the density of the ceramic materials.

Structural, paramagnetic centres and luminescence investigations of the UV radiation-emitting BaZrO3:Gd3+ perovskite ceramic prepared via sol-gel route

Perovskite-type ceramic materials have been widely studied due to their potential use in such applications as electrical, thermal, optical, and immobilizing host materials in nuclear waste. In this work, Gd3+-doped BaZrO3 perovskite samples were prepared by sol-gel method and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), electron paramagnetic resonance (EPR) spectroscopy, and photoluminescence (PL) analysis. Our XRD analysis confirmed the formation of the sol-gel products, and the SEM data implicated the prepared porous compound as the cause of the gases that evolved during the preparation. Upon excitation at 275 nm, the ceramic material displayed UVB emission at 315 nm (6P7/2 → 8S7/2). The EPR technique was used to study the undoped and gadolinium-doped perovskite BaZrO3 ceramics. The lines in the undoped system were caused by two defect centers. Center I displayed an isotropic line with a g-factor of 1.973 and a linewidth of 48 Gauss, and the center was assigned to an F+ center. Center II exhibited an axially symmetric g-tensor with principal values g|| = 1.895 and g⊥ = 1.978. This center was identified as the Zr3+ ion. The single dominant EPR line with an effective g-value of 1.976 that was observed in the Gd-doped system was attributed to the Gd3+ ion experiencing a weak cubic symmetry crystal field.

Microstructure and Piezoelectricity of (Na,K,Li)(Nb,Sb)O3–(Bi,Na)(Sr)ZrO3–BaZrO3 Ceramics

In this paper, (Na,K)1−xLi.x(Nb,Sb)O3–(Bi,Na)(Sr)ZrO3–BaZrO3 ceramics were fabricated with x(= Li) substitution by two-step sintering method, and their physical characteristics were investigated. When Li substitution was added to the ceramics, piezoelectric constant (d33) and electromechanical coupling factor (kp) were rapidly reduced. However, mechanical quality factor (Qm) was enhanced. For the KNN-BNZ((K,Na)(Nb)O3–(Bi,Na)(Sr)ZrO3) ceramics with Li(x) = 0 substitution, the best physical properties of d33 = 300 [pC/N], kp = 0.40, Qm = 33 and dialectic constant (εr) = 2430 were shown, respectively. Additionally, the KNN-BNZ ceramics with Li(x) = 0.02, the d33 of 246[pC/N], the kp of 0.37, the Qm of 42 and the εr of 2090 appeared, which were suitable for the low-loss piezoelectric actuator.

Dielectric relaxation behavior of BaZrO3 ceramics at low temperature

Dielectric behavior of nominally pure BaZrO3, Sc-doped BaZrO3 and Sc + Nb-co-doped BaZrO3 ceramics is reported in this paper. Several dielectric anomalies are detected in the pure and Sc-doped BaZrO3 in temperature interval of 2–700 K. The Arrhenius-type dielectric relaxation has activation energies ranging from ca. 10 meV–800 meV. Annealing in Ar atmosphere at 1200 °C alters the intensity of the dielectric loss peaks especially in the Sc-doped BaZrO3. In contrast, none of the dielectric relaxation anomalies were found in Sc + Nb-co-doped BaZrO3. It is proposed that at least some of the dielectric peaks originate from the proton dynamics which includes high temperature migration, intermediate-temperature rotation and low-temperature phonon-assisted proton tunneling.

Enhanced storage energy density and fatigue free properties for 0.94Bi0.50(Na0.78K0.22)0.50Ti1-x(Al0.50Nb0.50)xO3-0.06BaZrO3 ceramics

The high storage energy density (Wrec) and conversion efficiency (η) for lead-free ceramics have been attained significant interest in recent times for electronic devices. Enhanced Wrec and stable fatigue properties are examined for lead-free 0.94Bi0·50(Na0·78K0.22)0.50Ti1-x (Al0·50Nb0.50)xO3-0.06BaZrO3 (for 0 ≤ x ≤ 0.05) ceramics, synthesized using the solid-state reaction method. Crystal structure and lattice dynamics are revealed by the X-ray diffraction and Raman scattering techniques. Highly compact ceramics is obtained with decreasing average grain size from 0.94 ± 0.23 μm (for x = 0) to 0.76 ± 0.31 μm (for x = 0.05) as a function of composition. A high Wrec ~1.32 J/cm3 and η ~76.60% is achieved for x = 0.04 ceramic at room temperature with applied 95 kV/cm. In addition, Wrec ~1.40 J/cm3 and η ~86% are perceived with a 90 kV/cm at 80 °C. Also, it is obtained as a fatigue-free property for x = 0.04 composition ceramic up to 105 cycles. Hence, this improvement in energy density performance and stable fatigue resistance for x = 0.04 dielectric ceramic is expected for practical applications in many electronic appliances.

A Promising Proton Conducting Electrolyte BaZr1-xHoxO3-\u03b4 (0.05 \u2264 x \u2264 0.20) Ceramics for Intermediate Temperature Solid Oxide Fuel Cells

In this study, the Ho-substituted BaZrO3 electrolyte ceramics (BaZr1-xHoxO3-δ, 0.05 ≤ x ≤ 0.20) were synthesized through a low-cost flash pyrolysis process followed by conventional sintering. The effects of Ho-substitution in BaZrO3 studied in terms of the structural phase relationship, microstructure and electrical conductivity to substantiate augmented total electrical conductivity for intermediate temperature solid oxide fuel cells (IT-SOFCs). The Rietveld refined X-ray diffraction (XRD) patterns revealed that pure phase with Pmbar{3}m space group symmetry of cubic crystal system as originated in all samples sintered at 1600 °C for 8 h. The Raman spectroscopic investigations also approved that Ho incorporation in BaZrO3 ceramics. Field Emission Scanning Microscopic (FESEM) study informed a mixture of fine and coarse grains in the fracture surface of Ho-substituted BaZrO3 sintered samples. The relative density and average grain size of samples were observed to decrease as per the addition of Ho-substitution in BaZrO3 ceramics. The electrical conductivity study was accomplished by Electrical Impedance Spectroscopy (EIS) under 3% humidified O2 atmosphere from 300 to 800 °C. Furthermore, the total electrical conductivity of BaZr0.8Ho0.2O3-δ ceramic was found to be 5.8 × 10−3S-cm−1 at 600 °C under 3% humidified atmosphere, which may be a promising electrolyte for IT-SOFCs.

Influence of hydration and dopant ionic radius on the elastic properties of BaZrO3

The influence of point defects (acceptor dopants, oxygen vacancies, protonic defects) on the macroscopic elastic properties of acceptor-doped BaZrO3 ceramics is investigated. Ultrasonic pulsed echo time of flight measurements are used to study the impact of dopant size, concentration and degree of hydration. Ceramics of BaXxZr1-xO3-x/2+δH2δ with X = Y, Sc and 0.05 ≤ x ≤ 0.2 were prepared by solid state reactive sintering with NiO sintering aid, added to achieve mechanical robustness sufficient for high-degree (58–71%) hydration without disintegration. Introduction of the dopants causes linear decrease in the Young's and shear moduli. By comparing the rate of decrease upon doping with Y3+ and Sc3+, the contribution of the lattice expansion was separated from the contribution of vacancy formation. Dissociative water incorporation also decreases the elastic moduli, however, for the case of Sc-doping the effect of hydration on the elastic moduli is much larger. All experimental data agree well with predictions by ab initio calculations.

Remarkably strong piezoelectricity, rhombohedral-orthorhombic-tetragonal phase coexistence and domain structure of (K,Na)(Nb,Sb)O3–(Bi,Na)ZrO3–BaZrO3 ceramics

Demands for lead-free piezoelectric ceramics increase rapidly owing to environmental concerns. Strong piezoelectricity in (K,Na)Nb-based ceramics was usually realized by taking the advantage of rhombohedral-tetragonal (R-T) phase coexistence associating with the R-T phase transition. In this paper, we report the study results on a series of dense (0.96-x)(K0.48Na0.52)(Nb0.96Sb0.04)O3−0.04(Bi0.50Na0.50)ZrO3−xBaZrO3 ceramics (abbreviated as KNNS-BNZ-xBZ ceramics), in which the one with x = 0.01 shows a giant piezoelectric coefficient d33 of 610 pC/N with quite large electromechanical coupling coefficients of kp = 0.58 and k33 = 0.69. Dielectric measurement indicated that the rhombohedral-orthorhombic (R–O) phase transition temperature TR-O, orthorhombic-tetragonal (O-T) phase transition temperature TO-T and Curie temperature TC of this ceramic are −29 °C, 43 °C and 241 °C, respectively. Meanwhile, XRD analysis unveiled that this ceramic is in rhombohedral-orthorhombic-tetragonal (R-O-T) phase coexistence at room temperature. Acid etching revealed that domain structure inside the polycrystalline grains consists of lamellar domain stacks with a large amount of hierarchical nanodomain structure existing in part of the lamellar domains. The observed strong piezoelectricity is ascribed to the R-O-T phase coexistence and the corresponding characteristic domain structure.

Giant suppression of dielectric loss in BaZrO3

We report the effect of precursor's purity and heterovalent substitution on the microstructure and dielectric properties of BaZrO3 ceramics. We find that independent of the purity or raw materials, the dielectric loss of BaZrO3 at microwave frequencies is rather high with a Q factor in the range of 1000–3000 at 10 GHz. All stoichiometric ceramics studied show up to three types of low-T dielectric relaxations in the 2–250 K range. All these dielectric anomalies can be suppressed by partial substitution of Zr for Nb. By alloying of BaZrO3 with a hypothetical BaGa1/2Nb1/2O3 phase the Q × f value of ceramics at microwave frequency can be improved significantly. The origin of this remarkable improvement is attributed to the effect of the donor ions on the random electric fields and antiferrodistortive instability. Ceramic with a chemical composition of BaZr0.96Ga0.02Nb0.02O3 sintered at 1600 °C shows dielectric constant, ε′ = 36.7, temperature coefficient of the resonance frequency, τf = +110 ppm/°C and Q × f = 172 THz.

High-temperature dielectric relaxations in (Ce, Y) codoped BaZrO3 ceramics

(Ce, Y) codoped BaZrO3 ceramics, BaZr0.1Ce0.7Y0.2O3-δ and BaZr0.4Ce0.4Y0.2O3-δ ceramics were synthesized via solution combustion based on the glycine nitrate process. The dielectric properties of the samples have been investigated in the temperature range from 300 to 1000 K and frequency range from 102 Hz to 106 Hz. It is observed that the samples exhibit colossal dielectric behavior in the temperature below ∼600 K. The colossal dielectric behavior is composed of two sets of relaxations with the low- and high-temperature relaxations being caused by the dipole pairs of -Y and -Y, respectively. In the temperature higher than ∼600 K, the samples show two dielectric anomalies with extremely large dielectric permittivity over 106. It is argued that the low-temperature dielectric anomaly is the typical pseudo-relaxor behavior caused by ion-hopping-motion. While the high-temperature dielectric anomaly results from the negative capacitance effect.