Solid-state Sintering Method Research Articles

Advanced potassium ion batteries anode enhanced by Fe-doping strategy.

KVPO4F (KVPF) is a novel insertion-type anode for potassium ion batteries. For improving its electrochemical performance, the doping strategy was selected and a series of Fe-doped KVPF materials were synthesized by a facile solid-state sintering method to find out the suitable ratio. After comparation, KVPF sample with 5% Fe-doped ratio (KVPF/Fe-5) delivers the best performance, e.g. rate capacity (94.3mA h g-1 at 500mA g-1) and long-term discharge capacity (74.1 mA h g-1 after 1000 cycles at 200mA g-1, 0.03% capacity decay ratio per cycle), which is mainly attributed to its larger K+ diffusion rate. The in-situ X-ray diffraction analysis clarify the two-step K+ storage mechanism of KVPF/Fe-5 anode, and the density functional theory calculations verify that Fe-doping can reduce diffusion energy barrier of K+ and increase electronic conductivity of KVPF. When used as cathode, KVPF/Fe-5 delivers 51.8mA h g-1 at 100mA g-1 after cycling 200 cycles. In addition, the symmetric cell by employing KVPF/Fe-5 as anode and cathode simultaneously was also assembled successfully, pointing out a new research direction for potassium-ion batteries.

Improvement of microstructure and dielectric properties of Zn1.8SiO3.8 ceramics by doping with rare earth elements (La, Pr, Nd, Sm)

The current crucial focus is improving the performance of microwave dielectric ceramics, aiming for a low dielectric constant and minimal dielectric loss for millimeter-wave applications. In this study, we successfully synthesized Zn1.8SiO3.8-RO (R=La, Pr, Nd, Sm) microwave dielectric ceramics, namely ZLSO, ZPSO, ZNSO, and ZSSO, using the solid-state reaction sintering method. X-ray diffraction peaks indicated that the main phase matched the standard Zn2SiO4 diffraction peaks. As the dopant ion radius increases from Sm³⁺ to La³⁺, the diffraction peak shifts to a lower angle and the cell volume increases. Scanning electron microscopy revealed that the ZLSO, ZPSO, ZNSO, and ZSSO ceramics displayed denser and more uniform grain shape, along with a significant decrease in the densification temperature (1200°C-1250°C) compared to the Zn1.8SiO3.8 (1350°C-1400°C). Further research indicated that substituting rare earth ions maintained a low εr while effectively increasing the Q×f values. The specific properties are as follows: ZLSO: εr = 7.06, Q × f = 59,314GHz, τf = -25.00 ppm/℃; ZPSO: εr = 7.02, Q × f = 111,184GHz, τf = -17.77 ppm/℃; ZNSO: εr = 7.02, Q × f = 127,711GHz, τf = -33.52 ppm/℃; ZSSO: εr = 7.06, Q × f =108,435GHz, τf = -22.9 ppm/℃. Among them, ZNSO exhibited the best microwave dielectric performance. The research not only effectively produces microwave dielectric ceramics with outstanding performance but also systematically uncovers the distinct effects of rare earth elements doping on the dielectric properties of silicate systems. This provides the theoretical groundwork for utilizing 5G millimeter wave bands.

Magnetic properties and magnetocaloric effect of chromium-based high-entropy perovskite oxides

High-entropy oxides (HEOs) represent a significant advancement in the field of high-entropy ceramics and have received considerable attention in magnetism research. This study systematically investigated the magnetic and magnetocaloric properties of HEOs at low temperatures. To this end, three high-entropy perovskites metal oxides were designed using rare-earth transition metals ((R0.2Gd0.2Eu0.2Dy0.2Tb0.2)CrO3, R = Pr, Nd and Sm) because of their remarkable performance in magnetic refrigeration. The samples were prepared using solid-state sintering method and had a single-phase orthogonal distortion structure. All prepared samples exhibited weak antiferromagnetic properties and an antiferromagnetic–paramagnetic transition at lower temperatures. Further, the samples exhibited maximum magnetic entropy changes of 12.8, 13.1, and 13.6 J/kg K under a magnetic field intensity of 50 kOe with relative cooling powers of 153.05, 143.71, and 149.15 J/kg, respectively. An Arrott diagram indicated that all samples exhibited second-order phase transitions. The changes in the degree of spin ordering and the transition trends of the magnetic exchange interaction for each sample were analyzed at the phase transition temperature. The calculated magnetocaloric performance data indicate that these compounds exhibit excellent magnetocaloric properties and can be used as low-temperature magnetic refrigeration materials.

In-Situ Constructing N,S-Codoped Carbon Heterointerface for High-Rate Cathode of Sodium-Ion Batteries.

Na3V2(PO4)3 (NVP) is considered one of the promising choices for cathodes of sodium-ion batteries, but the poor conductivity resulted inferior rate performance limited the practical development of NVP cathodes. In this study, we successfully synthesized N/S dual-atom doped carbon coatings in situ through a simple one-step solid-state sintering method. The uniformly coated carbon layer can inhibit the agglomeration and growth of active materials during the sintering process, shorten the Na+ migration path, and increase the contact area with the electrolyte, thus facilitating rapid Na+ migration. Notably, the doping of N elements can alter the electron distribution of carbon coating, enhancing electron conductivity. Furthermore, the introduction of S elements in the carbon layer can induce the formation of stable C-S-C bonds in the molecular layer, expanding the interlayer spacing, which is beneficial for Na+ transport and storage. Therefore, the modified NVP@NSC composite provides a high specific capacity of 90.3 mAh g-1 at a rate of 20 C, with a capacity retention rate of 94.4% after 8000 cycles, demonstrating excellent stability at high current densities. Moreover, the full cell exhibits remarkable electrochemical performance at 5 C. This research contributes to the practical development of NVP cathodes.

Mn-Doped NaNbO3/Na0.5Bi0.5TiO3 Lead-Free Ferroelectric Ceramics with Enhanced Energy Storage Performance

NaNbO3-based ferroelectric composites are regarded as a highly promising typical energy storage material. In this work, 0.02xMnO2−(1−x)NaNbO3−xBi0.5Na0.5TiO3 composites were prepared by the solid-state sintering method and their microstructure, energy storage performance, and temperature stability were analyzed. As observed by the SEM images, the addition of Bi0.5Na0.5TiO3 to NaNbO3 in appropriate amounts can effectively suppress grain growth, which is beneficial for improving the breakdown field strength. When x = 0.3, an optimal value of 210 kV/cm is achieved. Meanwhile, as 2θ = 33.2°, the most intense XRD peak can be observed, indicating excellent solid solubility between the phase components. Consequently, 0.006MnO2–0.7NaNbO3–0.3Bi0.5Na0.5TiO3 composites demonstrated an impressive discharging storage density of 2.464 J/cm3 and a considerable energy storage efficiency of 85.8%. In addition, within the temperature range of 30–80 °C, the fluctuation in energy storage density remains below 10%. All the above performances indicate that this type of material exhibits excellent practicality in the field of pulse power supply.

Transparency and energy-storage characteristics of potassium tantalate niobate relaxorferroelectric ceramics

Transparent relaxor-ferroelectric ceramics with high energy density and good transmittance are indispensable for multifunctional electronic components. These ceramics have been widely used in transparent energy-storage electronics, advanced pulsed power capacitors, and optoelectronic multifunctional devices, etc. In this study, a novel Bi5+ and Li + co-doped transparent energy-storage ceramic with a nominal composition of (1-x)KTN-xLiBiO3 was prepared using traditional solid-state sintering method. The phase structure, microstructure, energy-storage performance, and transmittance of the ceramics were systematically investigated. The results indicate that a small amount of Bi5+ doped into the KTN matrix does not alter the perovskite structure of KTN. This work reveals that KTN ceramic exhibits a new feature, namely energy storage capability, with an energy-storage density and efficiency of W = 2.10 J/cm3 and 83.56 %, respectively. Moreover, this ceramic also exhibits a high discharge energy density of Wd = 1.52 J/cm3 and rapid charge-discharge rate of t0.9 = 5.6 μs. The ferroelectric and energy storage properties of these KTN ceramics also display good temperature stability. Meanwhile, the KTN ceramic also obtains good transparency, with the maximum transmittance of 55.78 % under 1100 nm light irradiation. This work provides a pathway for developing multifunctional materials and devices that combine transparency, ferroelectricity, and energy storage performance.

Synergistic modulation of SrTiO3-TiO2 colossal permittivity system by internal lattice defects and phase composition: Experimental and theoretical investigations

The SrTiO3–TiO2 composite ceramics with different contents of La doping were fabricated by traditional solid-state sintering methods. The performance of the colossal permittivity ceramics was enhanced by the synergistic design of the internal defect structure and phase composition. When the doping content is 2%, SrTiO3–TiO2 composite ceramics possessed a colossal permittivity (ԑr ∼ 1.1 × 105), low dielectric loss (tanδ ∼ 0.050) and favorable thermal stability (−70 °C-150 °C, ΔC/C25°C ≤ ±15%). Phase structure analysis suggested that a TiO2 secondary phase was induced at the grain boundaries of SrTiO3 phase with the addition of La3+ ions. XPS and dielectric behavior analyses revealed that oxygen vacancies and lattice defects formed by inhomogeneous ion-doping act to modulate the dielectric behavior in ceramics. The IBLC interfacial effects in relation to semiconductor grains and insulation grain boundaries are the main contributors to the colossal permittivity (CP) properties of ceramics, and the contribution of the IBLC effects becomes more prominent with increasing doping content. On the basis of first-principles analysis, the ceramic lattice undergoes severe deformation when the La content is increased, and the gathering of electrons at oxygen vacancies and defects is evident. As a result, it leads to enhanced grain semiconducting properties and interfacial effects, which facilitate colossal permittivity and low dielectric loss for ceramics. The results are prospective in the application of CP ceramics.

Significantly enhanced piezoelectric response in Aurivillius Bi3TiNbO9 ceramics simply by Ce doping

Bi3-xCexTiNbO9 (BTN-100xCe, x = 0, 0.01, 0.03, 0.05, 0.07, 0.09, 0.11) piezoelectric ceramics with ultra-high Curie temperature were fabricated by a solid-state sintering method, and the effect of Ce doping on the structure, dielectric and piezoelectric properties of the ceramics was investigated. All ceramic samples possess a single Aurivillius phase and Ce ions enter both A- and B-sites. Dense microscopic morphology with a remarkable decrease of grain size can be observed due to Ce doping. The resistivity markedly increases after Ce modification, and a significantly enhanced piezoelectric constant d33 of 17.1 pC/N can be achieved in the optimized BTN-7Ce ceramics, which is nearly 6 times that of pure Bi3TiNbO9 (d33 ≈ 3 pC/N). In addition to ultra-high Curie temperature (TC = 886.5 °C) and relatively high resistivity (ρ = 1.2 × 106 Ω cm @ 500 °C), the BTN-7Ce ceramics should be very promising for piezoelectric sensor under the application in high temperature conditions.

Codoping Pr3+ and Er3+ into NaLaTi2O6 to realize dual-mode FIR temperature sensing properties

In this report, a Pr3+/Er3+ doped NaLaTi2O6 phosphor was prepared as self-reference optical thermometer via a typical solid-state sintering method. The phase component, crystal structure and luminescence properties were elaborated in detail. A broad IVCT band along with several narrow 4f–4f excitation bands were readily found when monitored at 608 nm in Pr3+ singly doped NaLaTi2O6 material. In addition, the material showed typical 4f–4f transitions with two dominant bands around 495 nm and 609 nm originating from 3P0 → 3H4 and 1D2 → 3H4, respectively, upon ICVT or Pr3+ unique 4f–4f excitation. In Pr3+, Er3+ co-doped samples, the up-conversion (UC) emission bands around 522 nm, 548 nm and 661 nm, originating from characteristic transitions 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 of Er3+ ion was found, respectively, upon 980 nm radiation. Besides, the four main bands around 495 nm, 522 nm, 543 nm, 609 nm assigned to Pr3+ 3P0 → 3H4, Er3+ 2H11/2 → 4I15/2, Er3+ 4S3/2 → 4I15/2, Pr3+ 1D2 → 3H4, respectively, can be observed upon 379 nm co-excitation. By monitoring thermal responses emission intensities of versatile transitions under UC and down-shift (DS) excitation modes, good temperature sensitivity and signal discriminability based on FIR technique have been achieved in phosphor NaLaTi2O6:Pr3+, Er3+. Additionally, the maximal absolute temperature sensitivity Sa and relative temperature sensitivity Sr reach 0.0831 K−1 at 294 K and 1.15 % K−1 at 294 K under 980 nm excitation mode, and 0.01742 K−1 at 453 K and 1.826 % K−1 at 294 K under 379 nm excitation mode, respectively, indicating the prepared material in this work can be considered as a latent candidate for optical thermometry. More inspired, this work sets up a new pathway of codoping Pr3+ and Er3+ into suitable matrices to devise excellent FIR optical thermometry.

Enhancing response and thermal stability of PYN–PHT ceramics through design of "mixed-state" domain structures

Piezoceramics have long encountered difficulties in simultaneously attaining a high Curie temperature (TC) and extraordinary electrical characteristics due to the issue of thermal depolarization. To handle this, a novel 0.1 Pb(Yb0.5Nb0.5)O3 (PYN)–0.9 Pb(Hf1−xTix)O3 (PHT) + x mol%Ta2O5 piezoelectric ceramic was prepared using solid-state sintering method. We developed a synergistic strategy in introducing local heterogeneity into the tetragonal phase, where doping with heterovalent Ta5+ ions significantly reduces the temperature dependence of PYN–PHT piezoelectric ceramics. The structure and electrical behavior of obtained ceramics were methodically investigated using various analytical approaches. Our innovative composition, PYN–PHT–0.6Ta, showcases tetragonal phases. It exhibits impressive results, such as a piezoelectric coefficient d33 of 560 pC/N, an electromechanical coupling coefficient of 0.7 and a TC of 312.2 °C. Doping with Ta5+ ions unveils the formation of small size, mixed-state domain structure in enhancing piezoelectric and dielectric properties of ceramics. Additionally, the pinning effect of tetragonal phase contribute to the remarkable temperature stability (the variation in d33 is only 6.03 % from 25 °C to 300 °C) of the material. Overall, the exceptional performance and high quality of PYN–PHT–xTa ceramics hold great promise for high-temperature application in future microdevices.

Synthesis, Performance Measurement of Dy2EuSbO7/ZnBiDyO4 Heterojunction Composite Catalyst and Photocatalytic Degradation of Chlorpyrifos within Pesticide Wastewater under Visible Light Irradiation

For the first time, a novel catalyst named Dy2EuSbO7 was successfully synthesized via the high-temperature solid-state sintering method (HTSSM). Dy2EuSbO7/ZnBiDyO4 heterojunction photocatalyst (DZHP) was fabricated through the HTSSM for degrading chlorpyrifos (CPS) in the pesticide wastewater under visible light irradiation (VSLID). Under VSLID, DZHP could effectively degrade CPS in pesticide wastewater. The experimental outcomes suggested that the kinetic curve with the Dy2EuSbO7/ZnBiDyO4 heterojunction (DZH) as a photocatalyst for the reduction of CPS under VSLID conformed to the first-order kinetics (FOKT). After VSLID of 156 min, the photocatalytic degradation (PTD) removal rate of CPS using DZH as photocatalyst was 1.12 times, 1.21 times, or 2.96 times that using Dy2EuSbO7 as a photocatalyst, ZnBiDyO4 as a photocatalyst, or nitrogen-doped titanium dioxide as a photocatalyst. After VSLID of 156 min for four cycle degradation tests (FCDTS) with DZH as a photocatalyst, the removal rate of CPS reached 98.78%, 97.66%, 96.59%, and 95.69%, respectively. Above results indicated that the DZHP possessed high stability. Experiments with the addition of trapping agents showed that hydroxyl radicals (•OH) owned the strongest oxidative removal ability for degrading CPS compared with superoxide anions (•O2−) or holes (h+). The oxidation capacity of three oxidation radicals for eliminating CPS was ranked in the ascending order as follows: h+ < •OH < •O2−. Lastly, the possible degradation pathway and degradation mechanism of CPS were discussed in detail. A visible light responsive heterojunction catalyst with high catalytic activity and a photocatalytic reaction system which were capable of efficiently removing toxic organic pollutants from pesticide wastewater were obtained.

Effect of Dy2O3 doping on microstructure and electrical characteristics of ZnO linear resistors

ZnO linear resistors, due to its excellent performance, are widely used in numerous industries and gradually replacing traditional conductive resistors, presenting a broad prospect for application. To study the effects of lanthanide oxides on the microstructure and electrical properties of ZnO-based linear resistors, this paper prepared Dy2O3-doped ZnO-Al2O3-TiO2-NiO based linear resistors using a solid-state sintering method. The results showed that proper doping of Dy2O3 could inhibit the growth of ZnO grains, leading to more uniform grain growth. Additionally, doped with appropriate amount of Dy2O3 could enhance the linear performance of ZnO linear resistors, reduce the grain boundary barrier height (φb), and decrease dielectric loss. Linear resistors with nonlinearity coefficient (α) of 1.07, grain boundary barrier height (φb) of 0.0934 eV and resistance-temperature coefficient (αT) of −5.39 × 10−3/°C were obtained. The doping of Dy2O3 could improve the comprehensive performance of ZnO linear resistors, making the fabricated ZnO linear resistors are more suitable for working in high frequency electric fields. The study and analysis of Dy2O3 doped ZnO linear resistors are of significant importance for the preparation of high performance ZnO linear resistors.

Beneficial role of manganese dioxide for reducing surface resistivity to increase surface flashover voltage of vacuum insulating ceramics

Electric vacuum insulated devices generate surface flashover and breakdown under instantaneous high voltage. Flashover voltage can be increased through coating without changing the structure of the ceramic device. Herein, multiphase coatings with different manganese dioxide contents are prepared on α-Al2O3 insulating ceramic surface by screen printing and solid-state sintering methods to yield an average film thickness of about 12.38 μm with good bonding strength. X-ray diffraction shows that the crystal phases of the coating are (Al0.9Cr0.1)2O3 and MnAl2O4. Scanning electron micrographs and atomic force microscopy reveal that greater surface height difference and deeper surface depth are more conducive to increasing the surface roughness and the formation of "pores", and decreasing the surface potential decay rate. When MnO2 content is 0.0069 mol, the deep trap center energy level on the material surface reaches its maximum, increasing from 1.506 eV to 1.550 eV, and the surface resistivity of ceramics decreases from 1016 Ω to 1013 Ω. The formation of deep trap centers on the surface makes it difficult for surface charges to detach, which reduces the charge mobility and surface potential decay rate, and leads to decrease in surface resistivity and increase in surface flashover voltage.

Significantly improved energy storage performance of Na0.5Bi0.5TiO3–BaTiO3 ferroelectric ceramics with a wide temperature range via high-entropy doping

The emergence of high-entropy perovskite materials provides a new research idea to solve the problem of high remnant polarization and low recoverable energy storage density (Wrec) of relaxor ferroelectrics. In this study, barium-based high-entropy perovskite oxides Ba(Zr0.2Sn0.2Hf0.2Nb0.2Ti0.2)O3 (BZSHNT) were introduced into the 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 (BNT-6BT) ceramic by the conventional solid state sintering method. The 0.2BZSHNT doped BNT-6BT ceramic demonstrates significantly improved Wrec of 3.57 J/cm3 and a high efficiency of 81.6 % compared to those of the BNT-6BT ceramic, which is only 0.5 J/cm3 and 60 % respectively. The doped BZSHNT refines the hysteresis loops and drastically reduces the remnant polarization, which lead to the increase of the polarization difference. The 0.8(BNT-6BT)-0.2BZSHNT ceramics show high discharge energy density, good temperature stability (25–200 °C), excellent frequency stability (10–300 Hz) and superior discharge rate (t0.9 = 83 ns) because of its increased TiO6 lattice distortion, atomic disorder, relaxation degree and band gap, as well as the disruption of the long-range ordered ferroelectric domains. Our findings make BNT-6BT doped BZSHNT based ceramics one of the most promising lead-free dielectric energy storage candidates.

Crystal structures, dielectric properties, and lattice vibrational characteristics of Zn1-xCaxWO4 (x = 0–0.25) composite ceramics

In this work, Zn1-xCaxWO4 (x=0–0.25, ZCWO) composite ceramics were prepared by using the conventional solid-state sintering method at 1070 ℃. The impact of Ca2+ substitution on the lattice vibrational characteristics and dielectric responses of the ZCWO composite ceramics was investigated in detail. The formation of composite ceramics was verified by the Rietveld refined X-ray diffraction data of the ZCWO samples. The lattice vibrational characteristics were also identified and analyzed by the Raman and infrared reflection spectra combined with the theoretical simulations. The vibrational modes analysis of the Raman spectra showed that the internal modes of the ZCWO ceramics correspond to the vibrations of the W-O octahedrons. From the Fourier transform infrared reflectance spectra, the existence of three new vibrational modes of Au (315 cm−1), Au (834 cm−1), and Eu (885 cm−1) at x = 0.15–0.25 was observed, which belong to the modes of the CaWO4 ceramic. In addition, the intrinsic dielectric properties fitted by the four-parameter semiquantum model were in direct agreement with the theoretical values obtained from the Clausius-Mossotti & damping equations and the measured values. Besides, the contribution of each lattice vibrational mode to the intrinsic properties of the ZCWO ceramics was thoroughly studied, which shows that external mode 1 contributes the most to the intrinsic properties. The structure-property relationships of the ZCWO ceramics were established using the Raman modes as a media. The optimum dielectric properties of the ZCWO ceramics were obtained when x = 0.25: εr =13.98 (10.48 GHz), Q × f = 32,188 GHz.

Quaternary piezoelectric ceramics with ultra-high mechanical quality factor

The development of piezoelectric ceramics with large piezoelectric coefficient (d33), high Curie temperature (TC) and high mechanical quality factor (Qm) is still a key challenge for practical application for high-power device. Herein, a novel quaternary piezoelectric ceramics of (0.125-x) Pb0.98Sr0.02(Mg1/3Nb2/3)O3–0.445PbTiO3–0.43PbZrO3-xPb(Mn1/3Nb2/3)O3 (abbreviated as xPMnN-PSMN-PZT) were prepared by the solid-state sintering method. The hard dopant PMnN induced the morphotropic phase boundary (MPB) of PSMN-PZT into a tetragonal-rich region. In addition, the XPS and EPR analysis proved the existence of a large amount of oxygen vacancies (Vo••) in PMnN-PSMN-PZT ceramic system. The composition near tetragonal-rich MPB region and the appearance of defect dipoles formed a strong coupling effect on the domain wall motion and leaded to an ultra Qm value. The optimum piezoelectric properties were achieved at x = 9 mol% with d33 = 260 pC/N, Qm = 3880, tanδ = 0.009 and TC = 332 °C. A significant internal bias field (Ebias) of 8.83 kV/cm was also observed in 0.09PMnN-PSMN-PZT ceramics. The origin of this excellent piezoelectric properties was explained by the phase structure, piezoelectric and dielectric analysis. This work demonstrated a rational strategy to obtain ultra Qm value for high-power piezoceramics.

Microstructure, dielectric, ferroelectric and piezoelectric properties of K0.45Na0.45Li0.1NbO3 lead-free ceramics prepared via cold sintering with post-annealing

Via the method of cold sintering with post-annealing, the lead-free ceramics [Formula: see text][Formula: see text][Formula: see text]NbO3 were prepared. The cold sintered pellet without post-annealing shows a relative density ([Formula: see text] of 77.9%, which is larger than [Formula: see text] of the green pellet via the conventional solid-state sintering (SSS) method ([Formula: see text]). The cold sintered pellets were post-annealed at temperatures between [Formula: see text]C and [Formula: see text]C. The effect of post-annealing temperatures on microstructure, dielectric, ferroelectric and piezoelectric properties of the ceramics was studied in detail. After being post-annealed, the relative densities and grain sizes of the ceramics were increased. The ceramics post-annealed at [Formula: see text]C show excellent dielectric, ferroelectric and piezoelectric properties. Compared to the conventional SSS method, the method of cold sintering with post-annealing is successful in preparing dense [Formula: see text][Formula: see text][Formula: see text]NbO3 lead-free ceramics in a wide temperature range and at relatively low temperatures.

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.

(Sb0.5Li0.5)TiO3-Doping Effect and Sintering Condition Tailoring in BaTiO3-Based Ceramics.

(1-x)(Ba0.75Sr0.1Bi0.1)(Ti0.9Zr0.1)O3-x(Sb0.5Li0.5)TiO3 (abbreviated as BSBiTZ-xSLT, x = 0.025, 0.05, 0.075, 0.1) ceramics were prepared via a conventional solid-state sintering method under different sintering temperatures. All BSBiTZ-xSLT ceramics have predominantly perovskite phase structures with the coexistence of tetragonal, rhombohedral and orthogonal phases, and present mainly spherical-like shaped grains relating to a liquid-phase sintering mechanism due to adding SLT and Bi2O3. By adjusting the sintering temperature, all compositions obtain the highest relative density and present densified micro-morphology, and doping SLT tends to promote the growth of grain size and the grain size distribution becomes nonuniform gradually. Due to the addition of heterovalent ions and SLT, typical relaxor ferroelectric characteristic is realized, dielectric performance stability is broadened to ~120 °C with variation less than 10%, and very long and slim hysteresis loops are obtained, which is especially beneficial for energy storage application. All samples show extremely fast discharge performance where the discharge time t0.9 (time for 90% discharge energy density) is less than 160 ns and the largest discharge current occurs at around 30 ns. The 1155 °C sintered BSBiTZ-0.025SLT ceramics exhibit rather large energy storage density, very high energy storage efficiency and excellent pulse charge-discharge performance, providing the possibility to develop novel BT-based dielectric ceramics for pulse energy storage applications.

Microwave dielectric properties and LTCC applications of new glass-free molybdate ceramics Li3Ba2Ln3(MoO4)8 (Ln=Gd, Tm)

The traditional solid-state sintering method was employed to prepare Li3Ba2Ln3(MoO4)8 (Ln = Gd, Tm) ceramics, and the impact of firing temperature on the structure, microstructure and microwave dielectric properties of the novel molybdate Li3Ba2Ln3(MoO4)8 (Ln = Gd, Tm) ceramics was examined. XRD and Rietveld refinement outcomes validate the monoclinic system with the C2/c space group for Li3Ba2Ln3(MoO4)8 (Ln = Gd, Tm). For the Li3Ba2Gd3(MoO4)8 ceramic sintered at 800 °C, a εr is 9.42, a Q × f is 16,988 GHz, and a τf is 4.57 ppm/°C. The Li3Ba2Tm3(MoO4)8 ceramic sintered at 800 °C has a εr of 9.74, a Q × f of 25,401 GHz, and a τf of 1.08 ppm/°C. XRD and EDS analyses prove the good chemical compatibility of the co-sintered Li3Ba2Gd3(MoO4)8 ceramic with the Ag electrode. Therefore, the Li3Ba2Gd3(MoO4)8 ceramic is suitable candidate material for LTCC applications.