O3 Ceramics Research Articles

Tailoring performance of Bi(Ni0.50Ti0.50)O3–BiFeO3–Pb(Zr0.50Ti0.50)O3 ceramics via composition designing and sintering process improvement

Tailoring performance of Bi(Ni0.50Ti0.50)O3–BiFeO3–Pb(Zr0.50Ti0.50)O3 ceramics via composition designing and sintering process improvement

Structure evolution and microwave dielectric characteristics of Hf1−xSnxO2 ceramics

AbstractHigh Q (Hf1−xSnx)O2 ceramics were prepared via a standard solid‐state reaction route, and the microwave dielectric characteristics were investigated systematically together with the structure evolution. With increasing x, the structure changed from HfO2 (monoclinic in space group P21/c, x = 0 and 0.03) to Hf0.77Sn0.23O2 (orthorhombic in space group Pbcn, x = 0.23), while the two‐phase structure: HfO2 major phase and Hf0.77Sn0.23O2 secondary phase, was determined for x = 0.05–0.21, and Hf0.77Sn0.23O2 major phase combined with SnO2 tetragonal secondary phase in space group P42/mnm was confirmed for x = 0.30–0.40. The Qf value was significantly increased from 24,500 to 167,650 GHz by Sn‐substitution, and the best combination of microwave dielectric characteristics was obtained in Hf0.77Sn0.23O2 ceramics: εr = 17.2, Qf = 167 650 GHz at 9.6 GHz and 230 710 GHz at 26.1 GHz, and τf = −52.6 ppm/°C. The dielectric loss was deeply linked with the structure stability and lattice‐distortion. Also, the phase composition, the bond strength, as well as the degree of covalency, had a tight connection with dielectric loss. The present ceramics were expected to be the promising candidates as low‐εr microwave dielectric ceramics.

Large electrocaloric effect across the non-hysteretic electrostructural phase transition in lead-free (Ba0.88Ca0.12)(Ti0.94Sn0.06)O3 ceramics

Structural, dielectric, and electrocaloric properties were investigated in Pb-free ceramic (Ba0.88Ca0.12)(Ti0.94Sn0.06)O3 (BCST), synthesized using solid-state sintering method. Rietveld refinement of room temperature XRD data revealed the existence of pure perovskite tetragonal (P4mm) phase. Temperature-dependent XRD analyses confirmed a structural transition from tetragonal to cubic phase near 380 K. Temperature-dependent dielectric constant (εr) and specific heat capacity (Cp) confirmed the presence of thermal hysteresis in two phase transitions near 233 ± 10 K and 254 ± 10 K, and a non-hysteretic behavior at the Curie temperature (TC∼373 ± 10 K). A comprehensive Raman study corroborated the existence of phase transitions. Electrocaloric properties were determined using indirect method utilizing the non-hysteretic nature across TC. A large adiabatic temperature change of |∆T| = 0.52 K, isotropic entropy change |∆S| = 0.68 J/kg.K, electrocaloric coefficients, |∆T/∆E |= 0.311 K.mm/kV and |∆S/∆E| = 0.41 J.mm/K.kg.kV were obtained at 380 K for an electric field of 16.7 kV/cm. Obtained value of |∆T/∆E| is relatively good, reported among other BaTiO3-based ceramics.

Ultrahigh strain and superior temperature stability in lead-free ceramics via synergetic texture technique and phase structure engineering

Lead-free piezoelectric ceramics with large strain response and good temperature stability are highly required for actuator applications. However, the search for lead-free ceramics with both enhanced strain and reduced thermal-dependent behavior is a great challenge. In this work, by employing templated grain growth technique and elaborately modulate the phase structure, large unipolar strain of 0.30 %, low strain hysteresis Hs ∼ 12 %, along with small strain variation 11.8 % between 20 and 100 °C are achieved in (001)C-oriented (Ba0.95Ca0.05)(Sn0.04Ti0.96)O3 ceramics, being the optimal level of BaTiO3 family. It is revealed the ceramics exhibit a coexistence of orthorhombic and tetragonal phases. The inherent piezoelectric anisotropy of orthorhombic phase, the reversible a→c domain switch, along with the refined non-180° domain structures contribute to the remarkable electrostrain characteristic. This study proposed a promising strategy to develop high performance piezoelectric materials for actuator applications.

Effect of hetero-valence ions on structural and electrical properties of La2Ni(Mn0.5Ti0.5)O6 ceramics

The study of powder X-ray diffraction of La2Ni(Mn0.5Ti0.5)O6 (0.5LNMT) confirms a multi-phasic composition. The monoclinic P21/n phase content dominates. Occurrence of minor rhombohedral R3‾c phase and precipitates of MnO2 and La2MnO4 were detected. The morphology was analyzed using a SEM test and ceramics showed a porous structure and variation in the grain size below 4 μm. Dielectric permittivity of marked magnitude varies from ∼30 to ∼100 000 when temperature increases. Dielectric loss coefficient frequency dependence exhibits well-defined dielectric relaxation peaks, which were found to obey the Arrhenius law with the activation energy of 0.29 eV, below the presumed phase transition. Two sets of relaxation peaks in the imaginary part of electric modulus spectra relate to relaxations of different activation energies of 0.28 eV and 0.38 eV. An optical gap magnitude of 0.8 eV was determined from the diffuse reflectance spectrum in the Vis-NIR range. It compares with the band gap estimated from the X-ray photoelectron spectroscopy test. We also compare the influence of doping ions on the crystal lattice of the surface and the bulk ceramics. Electrical conductivity relaxation processes were attributed to the electron hopping mechanism between multi-valence Mnk+ and Nin+ ions’ states, which were determined from XPS analysis. The dc resistivity shows thermally generated dependence. Activation energy Edc magnitude varies between 0.27 and 0.37 eV which indicates the occurrence of defects and structural disorder. Such disorder correlates to the variable range hopping of small polarons involved in electrical conductivity. The density of states near Fermi energy was estimated N(EF) = 2.1 × 1025 eV−1 m−3. The 0.5LNMT application prospects were discussed.

Effect of Pr3+ doping on relaxation behavior and strain response of PHT-based piezoelectric ceramics

Heterovalent ion doping has influenced the further development of piezoelectric applications. Pr3+ doping in relaxor ferroelectrics is rarely focused on piezoelectric performance enhancement. 0.51 Pb(Ni1/3Nb2/3)O3-0.49 Pb(Hf0.3Ti0.7)O3 (PNN-49PHT) ceramics with Pr3+ doping ceramics were designed and fabricated by a two-step precursor method. Excellent dielectric diffusion coefficient (γ) of 1.96 was achieved at the low Pr3+ doping concentration of 0.2 %. Increased relaxation enhanced the nanoscale domains formation, resulting in a giant strain response (d*33) of 1400 pm/V at 10 kV/cm, and a total strain (Stol) of 0.27 % at 20 kV/cm. Structural refinement unveiled that the high piezoelectricity originated from the mainly substitution of Pr3+ for Pb2+ at the A-site, inducing lattice distortion and phase transitions. Local domain switching and long-range ordered destruction were investigated by piezoresponse force microscopy (PFM) and Scanning Electron Microscopy (SEM). These findings contribute to the advancement of piezoelectric devices and provide valuable insights for the design and optimization of high-performance piezoelectric ceramics.

Enhanced Thermoelectric Performance of Na0.55CoO2 Ceramics Doped by Transition and Heavy Metal Oxides

Using the solid-state reactions method Na0.55(Co,M)O2 (M = Cr, Ni, Zn, W, and Bi) ceramics were prepared and their crystal structure, microstructure, electrophysical, thermophysical, and thermoelectric properties were studied. Doping of Na0.55CoO2 by transition or heavy metal oxides led to the increase in the grain size of ceramics, a decrease in electrical resistivity and thermal diffusivity values, and a sharp increase in the Seebeck coefficient, which resulted in essential enhancement of their thermoelectric properties. The largest power factor (1.04 mW/(m·K2) at 1073 K) and figure of merit (0.702 at 1073 K) among the studied samples possessed the Na0.55Co0.9Bi0.1O2 compound, which also demonstrated the highest values of the Seebeck coefficient (666 μV/K at 1073 K). The obtained results show that the doping of layered sodium cobaltite by different metal oxides allows for improving its stability, microstructure, and functional properties, which proves the effectiveness of the doping strategy for developing new thermoelectric oxides with enhanced thermoelectric performance.

(Ag0.80Bi0.04Sr0.04)(Nb1-xTax)O3 ceramics with enhanced energy storage for high-temperature application via synergic optimization

Dielectric capacitors with high power density are essential components in advanced electronic and micro-electronic products. Nevertheless, the limited energy storage density and efficiency, coupled with poor performance at elevated temperatures, severely restrict their usefulness. In this work, Ta was introduced to the (Ag0.80Bi0.04Sr0.04)NbO3 ceramic prepared via the hydrothermal-synthesized powders to improve the room- and high-temperature energy storage performance. A large breakdown strength of 729kV/cm, a high recoverable energy storage density of 8.5J/cm3 and a benign energy efficiency of 75.6% were simultaneously achieved in (Ag0.80Bi0.04Sr0.04)(Nb0.85Ta0.15)O3 ceramics. Moreover, the larger energy storage efficiency (83.5%) at elevated temperatures than room temperature, the benign frequency and cycle stability foreshow great potential in realizing the application of capacitors at high-temperatures.

Achieving high energy-storage density and high temperature and frequency stability in 0.88BT-0.12BMT lead-free relaxor ferroelectric ceramics via NaNbO3 doping

In this work, 0.88BaTiO3-0.12Bi(Mg1/2Ti1/2)O3-xmol% NaNbO3 (x = 0, 0.5, 1, 1.5, 2) ceramics have been synthesized by using the traditional solid-state route. The effects of NaNbO3 on the phase structure, microstructure, dielectric, ferroelectric, and energy storage properties of the 0.88BaTiO3-0.12Bi(Mg1/2Ti1/2)O3 ceramics have been studied in detail. The ceramic doped with 1.5 mol% NaNbO3 exhibited a releasable energy storage density of 2.287 J/cm3, significantly higher than the undoped sample (1.194 J/cm3). The breakdown strength increases from 130 kV/cm for the undoped sample to 210 kV/cm for the sample doped with 1.5mol% NaNbO3. The enhanced breakdown strength of the 0.88BaTiO3-0.12Bi(Mg1/2Ti1/2)O3-xmol% NaNbO3 ceramics is primarily due to NaNbO3 doping, which produces a wider bandgap, smaller grain size, and higher specific resistance. The 0.88BaTiO3-0.12Bi(Mg1/2Ti1/2)O3-xmol% NaNbO3 ceramic's energy storage performance exhibits great temperature stability, frequency stability, and cycle stability at 120 kV/cm.

Excellent energy storage properties and multi-scale regulation mechanism of Sr(Zr0.5Ti0.5)O3-(Na0.5Bi0.5)0.94Ba0.06TiO3 ceramics

With the rapid advancement of energy storage technologies, dielectric capacitor materials with the outstanding recoverable energy density and power density have garnered significant attention from researchers in the past decades. In this study, (1-x) (Na0.5Bi0.5)0.94Ba0.06TiO3-xSr(Zr0.5Ti0.5)O3 ceramics were prepared via a solid-state reaction method, and the impact of composition on their structure, energy storage performance and stability were investigated. The results revealed that the introduction of Sr(Zr0.5Ti0.5)O3 induced the ferroelectric-relaxor transformation of (Na0.5Bi0.5)0.94Ba0.06TiO3 ceramics, leading to the destruction of the long-range ferroelectric order and the formation of polar nanoregions. In addition, the 0.7(Na0.5Bi0.5)0.94Ba0.06TiO3–0.3Sr(Zr0.5Ti0.5)O3 ceramic exhibited the optimal comprehensive energy storage performance: its recoverable energy storage Wrec attained 8.19 J/cm3 at 650 kV/cm, while the energy storage efficiency η was 85.6 %. Meanwhile, it displayed exceptionally high power density (315.7 MW/cm3) and charge-discharge rate (t0.9 = 50.4 ns). Moreover, this ceramic demonstrated the impressive energy storage performance, in particular, good temperature stability across a wide range of temperatures (20–140 °C), frequency stability (1–200 Hz), and fatigue resistance (1–106 cycles). Finite element analysis showed an enhancement in the breakdown field strength of the ceramics was attributed to the reduction in grain size. First-principles calculations revealed that the band gap increased after adding Sr and Zr elements, and the interactions between the states of O 2p and Ti 3d, Zr 3d, Bi 6p may serve as the microscopic origin of electron energy level polarization and enhanced dielectric performance. Thus, the ceramics have great potential for the application in high-power pulsed electronic systems.

Structural, Microstructural, and Electrical Properties Study of Pb(Sn0.45Ti0.55)O3 Ceramics

We undertook a comprehensive investigation of the the structural, dielectric, and electrical characteristics of Pb(Sn0.45Ti0.55)O3 ceramics prepared using the conventional solid-state route. A meticulous preparation protocol, involving solvating various precursors, was followed by extensive characterization employing X-ray diffraction, scanning electron microscopy, and dielectric studies. The synthesized sample features a single-phase tetragonal structure with P4mm symmetry. Using impedance spectroscopy, electrical transport properties of the polycrystalline Pb(Sn0.45Ti0.55)O3(PST) ceramic were studied in detail. Relaxation and conduction mechanisms of the material were inferred using complex impedance, complex electric modulus, and frequency dependent ac conductivity analysis. Impedance spectroscopy results reveal the range of frequencies in which the grain, grain boundary, and electrode effects are dominant. Above certain temperatures, the imaginary component of impedance (Z//) exhibits some resonant type peaks at different frequencies indicating relaxor nature of the sample. The activation energy obtained for both the relaxation and conduction process indicates the role of doubly-ionized oxygen vacancy in the conduction mechanism of the sample. The dielectric relaxation occurring at low frequency and high temperatures is related to the space charges associated with the ionized oxygen vacancies being trapped at the grain boundaries. The Cole-Cole plots confirm the poly-dispersive nature of dielectric relaxation in the sample.

The radiation resistance and chemical stability optimization of analog actinide nuclides incorporated Gd2Zr2O7 ceramics via grain size control

Gd2Zr2O7 is considered a promising host material for immobilizing high-level radioactive waste. However, its interplay between grain sizes, radiation resistance and chemical stability is not well understood yet. Herein, Gd1.7Nd0.3Zr0.5Ce1.5O7 ceramics with defect-fluorite phase and three different grain sizes (96, 390 and 1959 nm) were successfully fabricated and irradiated by 140 keV He ion beam up to a fluence of 8 × 1017 ions/cm2. Phase evolutions, microstructure changes and chemical stabilities were investigated. The nano-grained ceramic exhibits the lowest degree of amorphization and a delayed irradiation-induced lattice expansion and damage evolution process, demonstrating an enhanced ability in suppressing the coalescence of He bubbles inside the grain. Grain boundaries parallel to the surface were found to be more favorable sinks for irradiation-induced defects. Chemical stability tests showed that the 42 days leaching rates of all elements were between 10−7∼10−5 g/m2·d. All samples have maintained this superior chemical stability even after irradiation. Interestingly, the leaching test results also suggested that grain size may be not the primary factor influencing the long-term leaching rate.

Investigation of the Positive Temperature Coefficient Resistivity of Nb-Doped Ba0.55Sr0.45TiO3 Ceramics

The demands of low-Curie-temperature (~−10 °C) positive temperature coefficient (PTC) thermistors are increasing in advanced precision integrated circuits and other industries. In this paper, the Nb-doped Ba0.55Sr0.45TiO3(BST)-based PTC resistivity materials are reported. The effects of the sintering process, especially the cooling rate on the PTC properties of the material, are investigated. The results indicate that the Ba0.55Sr0.45Ti0.9985Nb0.0015O3 composition of the prepared PTC ceramics demonstrates promising PTC characteristics. These include a Curie temperature as low as −13 °C, a high temperature coefficient of 0.296 at −3.4 °C, a large enough resistivity change of 3.1 over a narrow phase transition temperature range of approximately 38 °C, and moderate resistivity below the Curie temperature. Such properties suggest that the Ba0.55Sr0.45Ti0.9985Nb0.0015O3 ceramics are likely suitable for use in thermal management systems designed for low-temperature control.

Structure, vacancy, and physical properties of non-stoichiometric MnWO4 ceramics

Non-stoichiometric ceramic samples of Mn0.97WO4 and MnW0.97O4 were prepared by a solid-state reaction to study the effects of vacancies at different lattice positions on the structure and properties of MnWO4 materials caused by non-stoichiometric. Positron annihilation technology was introduced to study the vacancy characteristics of the MnWO4, Mn0.97WO4, and MnW0.97O4 ceramics. The results indicated that non-stoichiometric did not affect the monoclinic lattice structure of any of the MnWO4 samples, and had no obvious effect on the lattice parameters of the samples. The analysis of positron annihilation lifetime spectroscopy showed that W vacancies were the main defects in MnW0.97O4 samples, and Mn vacancies were favored in Mn0.97WO4 samples, the vacancies concentration for non-stoichiometric MnWO4 samples was higher than that of stoichiometric MnWO4. It was observed that the magnetization and transition temperatures of the non-stoichiometric MnWO4 system were increased, and the temperature range in which AF2 phase existed was enlarged. This study demonstrated that non-stoichiometric could enhance the magnetic properties of MnWO4, the effect of Mn vacancy on the properties of MnWO4 is higher than that of W vacancy. The intimate correlation between the vacancy defects and magnetic properties provides us strong evidence that the magnetic properties of MnWO4 can be enhanced by regulating vacancy defects.

Achieving high energy storage performance in PbHfO3-based antiferroelectric ceramics by Sr element doping

Antiferroelectric (AFE) ceramics are the most promising material system for energy storage in dielectric capacitors due to their fast charging-discharging rate, good chemical stability, and high energy storage density. However, it is exceedingly challenging to simultaneously achieve the excellent recoverable energy density (Wre) and high energy storage efficiency (η) at present. In this work, (Pb0.925-xSrxLa0.05)(Hf0.95Ti0.05)O3 AFE ceramics with various Sr contents are fabricated by solid-state sintering processing. It has been found that Sr-doping in the A-site can significantly affect the microstructure, including reducing grain size and modulation period, effectively strengthening the antiferroelectricity, which is responsible for the improved energy storage performance. The high recoverable energy storage density of 10.2 J/cm3 is obtained at 560 kV/cm with an ultra-high efficiency of 93.0% in (Pb0.875Sr0.05La0.05)(Hf0.95Ti0.05)O3 ceramics. These features suggest that Sr-doped PbHfO3-based AFE ceramics can serve as promising candidates for capacitor materials, offering significant potential in the realm of energy storage applications.

Microstructure of the spark-plasma sintered pyrochlore ceramics based on Bi2O3-ZnO-Nb2O5 system

The spark-plasma sintering of ceramics based on the cubic pyrochlore phase in the system Bi2O3-ZnO-Nb2O5 is reported for the first time. It is shown that the use of spark-plasma sintering in the manufacture of (Bi1.5Zn0.5)2(Zn0.5Nb1.5)2O7 ceramics makes it possible to obtain a high density, a homogeneous microstructure, and high dielectric parameters (almost 30% higher compared to conventional ceramic technology). The paper discusses the features of microstructure formation and the optimization of spark plasma sintering regimes.

3D printing of CaBi4Ti3.925(Nb2/3Mn1/3)0.075O15 ceramics for high temperature ultrasound transducer

Bismuth layer-structured CaBi4Ti3.925(Nb2/3Mn1/3)0.075O15 (CBTNM) piezoelectric ceramics have been prepared using stereolithography (SL) technology. The effects of various solid contents (76–82 wt%) of CBTNM ceramics on the slurry viscosity, phase structure, microstructure, and electric performance were studied in detail. At a solid content of 82 wt%, the ceramic exhibits good piezoelectric properties. The piezoelectric constant d 33, thickness-mode electromechanical coupling coefficient k t, and Curie temperature Tc were 21 pC/N, 47%, and 790 °C, respectively. The piezoelectric constant of the ceramic has a good stability up to 500 °C. Furthermore, a high-temperature ultrasound transducer was designed and fabricated based on the CBTNM ceramic, and its pulse-echo performance was characterized from room temperature to 250 °C. The pulse-echo performance indicates that the −6 dB bandwidth and echo amplitude of the transducer decrease slightly, but still work normally up to 250 °C. These results indicate that the transducer fabricated based on CBTNM ceramics has potential in high-temperature testing applications.

High energy density in Ag0.5Na0.5(Nb1-xTax)O3 antiferroelectric ceramics

There has been significant interest in AgNbO3-based antiferroelectric ceramics, recently, due to their ability to achieve high energy storage density (Wrec). However, fabricating their commercial products faces challenges due to chemically unstable and expensive Ag2O. To reduce Ag2O contents, we fabricated (Ag0.5Na0.5)(Nb1-xTax)O3 (ANNT100x) ceramics. The results reveal that Ta-substitution plays a dual role: inducing chemical pressure to compress the unit cell along spontaneous polarization direction, enhancing antiferroelectric stability; and increasing the band gap (Eg), boosting intrinsic breakdown strength (Eb). These crucial factors contribute to the enhanced Wrec achieved in ANNT50. Notably, ANNT50 ceramics fabricated by the rolling process exhibit higher Eb (=578 kV/cm) than the conventional process, favoring the complete triggering of “double” polarization with significantly enhanced Wrec (= 6.5 J/cm3). Discharge results indicate that the ceramic displays high power density (Pavg = 78 MW/cm3) and discharge energy (Wdis = 5.86 J/cm3), which can rival currently reported Ag(Nb, Ta)O3 ceramics.

Enhanced energy-storage properties in (Bi0.5Na0.5)TiO3 ceramics by doping linear perovskite materials Ca0.85Bi0.1(Sn0.5Ti0.5)O3

For energy storage applications in Bi0.5Na0.5TiO3 (BNT)-based materials, the key challenges are the premature polarization saturation and low breakdown electric field (Eb), which confine the energy storage capacity of BNT and significantly restrict progress in advancing pulsed power capacitors. Hence, the cooperative optimization strategy of band structure and defect engineering was proposed, which successfully obtained a high recoverable energy density of 3.83 J/cm3 and an energy efficiency of 77.9 % in the Bi0.5Na0.5TiO3-0.12Ca0.85Bi0.1(Sn0.5Ti0.5)O3 (BNT-0.12CBST) ceramics. Doping the BNT matrix with CBST has been shown to not only reduce grain size but also enhance relaxor behavior, which collectively improves breakdown strength and delays polarization saturation. Furthermore, the x = 0.12 ceramic also exhibits a commendable discharge power density of 91.9 MW/cm3 and a transient discharge time of 40 ns. The higher resistivity and lower oxygen vacancy concentration are conductive to acquire superior breakdown electric field and energy storage performance. We determine the crystal structure, dielectric and ferroelectric properties of the studied ceramics in a wide range of temperatures and concentrations, and a phase diagram is constructed, which illustrates the complex phases present and their transformation behavior. Our work provides an effective strategy to optimize the energy-storage of dielectric ceramics, and shows great potential for practical applications in pulse power systems.

Enhanced dielectric, ferroelectric and piezoelectric properties of lead-free (Ba,Ca)(Sn,Ti)O3 ceramics by optimisation of sintering temperature

Lead-zirconate-titanate [Pb(Zr,Ti)O3 PZT] crystals possess superior ferroelectric, dielectric and piezoelectric properties. However, due to the toxicity of lead there is a demand for lead-free alternatives. In the present work, we focus on the production of the lead-free (Ba,Ca)(Sn,Ti)O3 (BCST) ceramics via solid-state synthesis method. BCST ceramics calcined at 1050°C, 1100°C, 1150°C, 1200°C and 1250°C were characterized using XRD analysis which showed that at temperatures above 1150°C the structure was free from impurities. Rietveld refinements confirmed a tetragonal structure with P4mm space group for the material calcined at 1150°C. Scanning electron microscopy image analysis of samples sintered at 1200°C, 1250°C and 1300°C showed an increase in grain size and density with temperature. The material sintered at 1300°C had a higher dielectric constant compared to other ceramics. A larger grain size facilitated high ferroelectric polarisation (3.38 μC/cm2), dielectric constant (6100) and d33 piezoelectric coefficient (236 pC/N) for the ceramics. This study demonstrates the potential for using lead-free BCST ceramics for device applications, such as piezoelectric actuators, transducers and ultrasonic motors.