Conventional Solid-state Sintering Research Articles

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.

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.

(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.

Enhanced energy storage properties of (Ba0.4Sr0.6)TiO3 ceramics with ultrahigh energy efficiency through doping of Bi0.2Sr0.7(Mg1/3Nb2/3)O3

Dielectric (Ba0.4Sr0.6)TiO3 (BST) ceramics are promising dielectric energy storage materials due to their moderate dielectric constant, low dielectric loss, and slight nonlinearity. However, their energy density is limited by their low breakdown strength (BDS). In this study, we aimed to address this limitation by incorporating various amounts of Bi0.2Sr0.7(Mg1/3Nb2/3)O3 (SBMN) into the BST matrix. The (1–x)BSTxSBMN ceramics were prepared by conventional solid-state sintering, resulting in single-phase solid solutions. Compared to pure BST ceramics, the (1–x)BST–xSBMN ceramics exhibited lower remnant polarization and significantly enhanced BDS. Furthermore, the relaxation of the ceramics enhanced with increasing doping concentration, with an efficiency of η = 94.0% achieved at x = 0.20. Among them, the breakdown field strength of 0.85BST–0.15SBMN ceramics was 597 kV cm−1, achieving a recoverable energy storage density of Wrec = 2.81 J cm−3 and an efficiency of η = 90.8% under an external electric field of 480 kV cm−1. Subsequent tests revealed that the introduction of SBMN not only increased the band gap and conduction activation energy of the material, leading to an increase in BDS, but also promoted the formation of polar nanoregions (PNRs) which contributed to boosted energy efficiency, resulting in a significant enhancement in the energy storage performance of BST ceramics.

Investigating Fe-doped Ba0.67Ni0.33Mn1-xFexO3 (x = 0, 0.2) ceramics: insights into electrical and dielectric behaviors.

This study investigates the characteristics of the Ba0.67Ni0.33Mn1-xFexO3 perovskite compound, focusing on its structural and electrical aspects under varying Fe doping levels at the Mn-site (x = 0, 0.2). X-ray diffraction patterns confirm the material's consistent structure, with Fe3+ ions substituting Mn3+ ions while maintaining their identical ionic radius. Nano-crystallinity studies reveal single-phase crystallization in the orthorhombic structure with space group Imma. Samples are prepared through conventional solid-state sintering. The Williamson-Hall method calculates crystallite sizes, averaging 37 nm for x = 0 and 33 nm for x = 0.2. Electrical properties are examined using complex impedance spectroscopy at different temperatures and frequencies. Techniques such as energy dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM) assess chemical composition. Activation energy values increase from 0.138 eV for x = 0 to 0.171 eV for x = 0.2, leading to reduced dc conductivity across the investigated temperature range. Dielectric permittivity enhances proportionally with increasing Fe doping. Variations in impedance profiles reveal a relaxation phenomenon. A circuit model, Rg + (Rgb//CPEgb), elucidates impedance data. This study illuminates the interplay between Fe doping, activation energy, and electrical conductivity in Ba0.67Ni0.33Mn1-xFexO3 perovskite, offering insights applicable to electronic and energy-related devices. Perovskite-based nanomaterials have diverse environmental applications, including solar cells, light-emitting devices, transistors, sensors, and energy storage.

Highly efficient preparation of 0.2ZrO2/ZrSiO4 bulk ceramics with high density and hardness by molten-salt method and hot-pressing sintering

Using conventional solid state sintering method to synthesize ZrSiO4 ceramics may result in high temperature and time consumption. Herein, a novel preparation route combining the advantages of molten-salt method and hot-pressing sintering (MH) was developed and used to efficiently prepare 0.2ZrO2/ZrSiO4 ceramics (Z/Z). The phase structure, micromorphology, compactness and hardness of the obtained ceramics affected by the salt to oxide ratio, sintering temperature and holding time were investigated and discussed. It was found that the obtained Z/Z ceramics with high density (95.44 % of theoretical density) and high hardness (12.77 GPa) were prepared by the MH at low temperature and short holding time. The discussion of the results revealed that the optimum ratio of salt to oxide was 10: 1, molten-salt sintering conditions were 1300 °C and 6 h, hot-pressing sintering conditions were 64 MPa, 1200 °C and 0.5 h. The results demonstrated that the novel preparation route could be extended to prepare other high-performance ceramics.

Microstructural and physical characterizations of (1-x)(0.67BiFeO3+ 0.33BaTiO3+ 1%MnO2)− x(CoFe2O4+ 3%ZnO) magnetoelectric composites

BiFeO3 (BFO) was mixed with BaTiO3 (BTO) to form a solid solution of large piezoelectric coefficient (d33) for the fabrication of magnetoelectric (ME) composites with the Zn-doped CoFeO4 (CFO). The 0.67BFO+0.33BTO solid solution, which was doped with 1 at% MnO2 for lowering leakage current, showed a high d33 of 121 pC/N. However, in the composites made with CFO, a much lower d33 (<42 pC/N) was retained. The microstructure of the composites was featured by the large CFO grains (∼5 μm) embedded in the 0.67BFO+0.33BTO matrix of much finer grains (∼0.5 μm). The CFO grains each had a well-defined morphology with clear boundary discriminating them from the neighboring piezoelectric phase. Both the CFO and piezoelectric grains showed a high crystallinity as indicated by the appearance of clear Kikuchi patterns in electron backscattered diffraction. After reducing DC conductivity of CFO by Zn-doping and the optimization of fractional ratio of the Zn-doped CFO in the composites, a ME voltage coefficient of 81.8 mV/cm-Oe was achieved, which was high among the lead-free particulate ME composites prepared by the conventional solid-state sintering.

Microstructure and nonlinear electrical properties in Na2CO3-ZnO varistor ceramics

Herein, (1-x)ZnO + xNa2CO3 (x = 0, 0.5, 1.0, and 1.5 mol%) varistor ceramics were prepared via conventional solid-state sintering at a low sintering temperature of 900 ℃. The microstructure and electrical properties of these varistor ceramics were systematically investigated as a function of Na2CO3 concentration. Results revealed that the prepared varistor ceramics exhibit the hexagonal structure without a secondary phase. The increase of Na2CO3 concentration promotes the ZnO grain growth. Owing to an increasement in the barrier height at the grain boundaries, the nonlinear electrical properties of the ceramics considerably improve with increasing Na2CO3 concentration. The optimal composition of 98.5 mol%ZnO + 1.5 mol%Na2CO3 corresponds to a nonlinear coefficient of 3.55, leakage current density of 450 μA/cm2, breakdown strength of 241.2 V/mm, and barrier height of 0.57 eV. Moreover, the dielectric properties of the varistor ceramics are considerably affected by Na2CO3 concentration.

Cracking behavior of Sm2O3 ceramics and enhanced microwave dielectric properties with MgO addition: Insights from chemical bond characteristics and microstructure

Monoclinic Sm2O3 ceramics were prepared using the conventional solid-state sintering method. The influences of sintering temperature on structure, morphology, and performance of Sm2O3 ceramics were studied systematically. The excellent microwave dielectric properties (εr = 21.95, Q × f = 47,000 GHz, and τf = +30.15 ppm/°C) were achieved in Sm2O3 ceramic sintered at 1550 °C for 4 h. Interestingly, varying degrees of cracking were observed after the sintered samples were placed for a short time, with the extent depending on the sintering temperatures. The reasons for cracking were analyzed through chemical bond characteristics and microstructure. The analysis of bond valence and microstructure revealed that Sm2O3 ceramics sintered at higher temperatures exhibited larger bond strain index, global instability index, and interplanar spacings. These results suggest that the cracking of Sm2O3 ceramics originates from inner stress resulting from structural variations caused by variations in sintering temperatures. The effect of MgO addition on microwave dielectric properties and stability of Sm2O3 ceramics was also investigated. Phase identification and elemental distribution indicated that MgO existed as a secondary phase. The Sm2O3 ceramic with 20 wt% MgO addition exhibited optimal microwave dielectric properties: εr = 17.72, Q × f = 61,100 GHz, and τf = +2.4 ppm/°C. Importantly, cracking was not observed when MgO addition amounts were 5 wt% or higher. The attractive microwave dielectric properties and favorable stability confirm the possibility of the 5G applications for Sm2O3/MgO composite ceramics.

Improved dielectric temperature stability and energy storage properties of BNT-BKT-based lead-free ceramics

The lead-free ceramics (1-x)(0.84Bi0.5Na0.5TiO3-0.16Bi0.5K0.5TiO3)-xBiMg2/3Nb1/3O3 (denoted as (1-x)BNKT-xBMN) and (1-y)(0.85BNKT-0.15BMN)-ySr0.7La0.2TiO3 with y = 0.3 (denoted as BNKMN-0.3SLT) were prepared by means of a conventional solid state sintering method. Effects of introduction of BiMg2/3Ni1/3O3 and Sr0.7La0.2TiO3 on phase structure, microstructure, and dielectric, ferroelectric and energy storage properties of the ceramics were studied in detail. The ceramics (1-x)BNKT-xBMN show pure perovskite structure, while BNKMN-0.3SLT appears a secondary phase. All ceramics exhibit dense microstructures with mean grain sizes between 0.56 μm and 1.36 μm. The introduction of SLT into BNKMN causes obvious decrease in dielectric constant around Curie temperature, inducing the widest temperature window of 263 °C from 29 °C to 292 °C for TCC≤±15 %. The ceramic BNKMN-0.3SLT shows high electric breakdown strength (Eb ∼ 300 kV/cm), large maximum polarization (Pm ∼ 36.48 μC/cm2), and low remanent polarization (Pr ∼ 1.70 μC/cm2), inducing high energy storage density of 4.03 J/cm3 as well as high energy storage efficiency of 85.2 %.

Enhanced electrocaloric effect in KNN-based ceramic via polymorphic phase transition

A large adiabatic temperature change (ΔT) in lead-free ceramics is highly desired to develop eco-friendly and high efficiency solid-state refrigeration device based on electrocaloric effect (ECE). However, a large ΔT is often obtained near high Curie temperature (Tc > 100 °C), which impedes the practical applications for electrocaloric refrigeration technology. Herein, the lead-free (1-x)(K0.48Na0.535)0.03Li0.07(Nb0.99Sb0.01)O3-xBaZrO3 (x = 0, 0.02, 0.04 and 0.06) ceramics were synthesized through a conventional solid-state sintering method. A polymorphic phase transition (PPT) region is constructed by composition engineering to achieve large ECE near the ambient temperature. A ΔT of 0.48 K under 50 kV/cm is obtained at 60 °C by using the direct measurement in KNLNS-0.02BZ ceramic with coexistence of R-O-T phase. This work suggests that building multi-phase coexistence is a feasible design scheme in order to achieve ECE near the room temperature.

Electrocaloric effect, pyroelectric response and energy storage performance of lanthanum-modified PZT relaxor ferroelectric ceramic

Pb0·85La0·10Zr0·60Ti0·40O3 ferroelectric ceramic system was synthesized via the conventional solid-state reaction sintering route. A systematic study on the pyroelectric response, electrocaloric effect and energy storage properties has been carried out in a wide temperature range, in order to explore its multifunctional features. The obtained results from X-ray diffraction technique, performed at room temperature, revealed the coexistence of two ferroelectric phases governed by the tetragonal (P4mm) and monoclinic (C1m1) symmetries. The pyroelectric behavior of the studied sample has been analyzed by the static method, from the temperature dependence of the pyroelectric current. The electrocaloric response as well as the energy storage performance have been investigated from the ferroelectric hysteresis loops (P−E curves), at 50 kV/cm, covering a wide temperature range. The obtained results revealed a ferroelectric ceramic composition with suitable properties and strong potential to be used in multifunctional electronic devices based on pyroelectric sensors combined with high efficiency energy storage performance and solid-state refrigeration technologies.

Significantly enhanced performance and conductivity mechanism in Nb/Mn co-doped CaBi4Ti4O15 ferroelectrics

With the rapid development of high-end industries, the demand for high-temperature piezoelectric materials is significantly increasing. However, realizing the ultra-high performance to meet more applications still faces major scientific and engineering challenges of our time. Here, a new Nb/Mn co-doped CaBi4Ti4O15 (CBT) high-temperature piezoelectric material system of CaBi4Ti4-x(Nb2/3Mn1/3)xO15 was synthesized by the conventional solid-state sintering method. The results show that the addition of the dopants tends to break the long-range ferroelectric chain and soften the flexibility of polarization, resulting in more distorted crystal structure and better ferroelectric properties of CBT ceramics. The ultra-high piezoelectric constant (d33 = 26.8 pC/N) is thus attained in CBT-based ceramics with x = 0.12, which is about several times larger than that of pure CBT ceramics. Moreover, numerous nano-sized layered domain structures that lie on the lateral plane of grains are observed in ceramics, with lower domain wall energy and better dynamic features under electric fields, mainly responsible for the origin of enhanced performance. Besides, excess dopants could make the conductivity mechanism of CBT ceramics transform from p-type to n-type, and also result in a shift of conduction relaxation mechanism from defect dipole rotation polarization to electron relaxation polarization. The work not only provides a promising candidate for high-temperature piezoelectric materials, but also opens a window for optimizing performance by tailoring domain structures using chemical modification.

Phase Formation, Microstructure and Electric Properties of Vanadium Doped Lead-Free BaTi0.91Sn0.09O3 Ceramics

Lead-free Ba(Ti0.91Sn0.09)1-xVxO3 (BTSV, x = 0, 0.005,0.010, 0.015, and 0.020) ceramics were prepared by the conventional solid-state sintering method with a calcination temperature of 1200 °C for 2 h and a sintering temperature between 1350 °C and 1400 °C for 4 h. The effect of vanadium (V) doping on the phase formation, microstructure and electrical properties of the ceramics was investigated. X-ray diffraction (XRD) measurements revealed that the ceramics with x = 0 and 0.005 had pure perovskite structures with no detectable impurity, while the ceramics with x ≥ 0.010 exhibited perovskite structures and had secondary impurity phases. Coexisting orthorhombic and tetragonal phases were observed and the Rietveld refinement analysis suggested that the tetragonal phase increased with increased V5+ substitution. When x increased from 0 to 0.010, the average grain size increased from 47 to 62 µm and then dropped, while the density (ρ) decreased from 5.98 to 5.64 g/cm3 when x increased. Furthermore, the BTSV ceramics exhibited increased porosity, Curie temperatures (T C ∼ 42 °C to 52 °C) and coercive field (E c), while the dielectric constant at the Curie temperature (εC) and the remnant polarization (P r) of the ceramics decreased (∼18023 to 6110 and ∼7.42 to 4.88 µC/cm2, respectively) when V5+ doping increased.

Visualizing sintering process and electrical properties of SnO2 doped K0.48Na0.52NbO3 piezoelectric ceramics

In this study, the conventional solid-state sintering of lead-free (1−x)K0.48Na0.52NbO3-xSnO2 piezoelectric green bodies was analysed using thermal imaging and longitudinal/transverse shrinking. The phase structure, fracture morphology, densification, permittivity, ferroelectricity, piezoelectricity, and domain-switching activation energy were investigated with increasing SnO2 content (x). Sn4+ first occupied the A site in the ABO3 structure and then substituted the B site with increasing x. This resulted in various contents of defect dipoles and oxygen vacancies, which were mainly responsible for the different ferroelectricity and piezoelectricity values. The permittivity and domain-switching activation energy were significantly affected by the local compositional disorder or fluctuation. Moreover, the influences of phase, densification, fine grain size, and domain wall on the electrical properties are also discussed. The optimum electrical properties, with Pr = 34.7 μC/cm2, d33 = 294 pC/N, and TC = 337 °C were determined for x = 0.30 mol%. This study provides a specific explanation and reference for the various electrical properties of lead-free piezoelectric ceramics.

A novel thermally-stable single-phase phosphor Ca2InTaO6:Dy3+ for NUV-excited white LEDs

The work focuses on the utilization of the conventional solid-state sintering procedure to synthesize white phosphors Ca2InTaO6:xDy3+ (0.02 ≤ x ≤ 0.12). Utilizing X-ray diffraction, the phase structure of samples was examined, and the crystal structure was refined using the Rietveld method. A scanning electron microscope was used to analyze the microstructure of sample. First-principles calculations confirm that the indirect bandgap of Ca2InTaO6 is 3.786 eV. The luminous properties and energy transfer mechanism of Ca2InTaO6:xDy3+ were studied using photoluminescence spectroscopy. The 4F9/2 → 6H13/2 transition of Dy3+ ions is responsible for the greatest emission peak, which was measured at 575 nm. According to research, the lifespan falls as the concentration of Dy3+ doping amount rises because of frequent interaction and energy transfer between Dy3+ ions. The correlated color temperature of the W-LEDs packaged with Ca2InTaO6:0.08Dy3+ is 4677 K and CIE 1931 chromaticity coordinates are (0.3578, 0.3831). Meantime, the phosphor also shows outstanding temperature stability property, which maintains 83.8% of its initial emission intensity at 450 K (activation energy of 0.1467 eV). The W-LEDs retain their performance for 100 min when powered at 3.4 V voltage and 600 mA current, demonstrating the packed W-LEDs' sustained operation at high temperatures.

Enhanced energy storage properties of Bi0.5Na0.5TiO3-based ceramics via regulating the doping content and sintering temperature

Eco-friendly lead-free energy-storage ceramics featuring high energy storage properties and ultra-high stability have been regarded to be one of the most potential materials in the field of energy storage. In this work, a new element system, (1-x)(0.6Bi0.5Na0.5TiO3-0.4SrTiO3)-xBi[Zn2/3(Nb0.5Ta0.5)1/3]O3 ((1-x)BNST-xBZNT) lead-free ceramics, were synthesized via a conventional solid-state sintering technology. And the phase structure, microstructure and energy storage properties of the (1-x)BNST-xBZNT ceramics were comprehensively studied. After the introduction of BZNT, the average grain size of the materials is greatly decreased, thereby enhancing the dielectric breakdown strength (DBS). Additionally, the thermal stability of the ceramics is significantly improved via regulating the doping content and sintering temperature. Furthermore, the ferroelectric long-range order of the ceramics is decomposed into randomly-oriented polar nano-domains (PNRs) after introducing BZNT, leading to strong relaxor behavior and significantly reducing remanent polarization (Pr). As a result, even under a relatively low electric field of 139 kV/cm, the 0.98BNST-0.02BZNT ceramic sintered at 1150 °C possesses high values of energy storage efficiency (η) value of 92.78% and total energy storage density (Wtot) of 1.67 J/cm3 as well as remarkable thermal stability (25–175 °C), frequency stability (20–70 Hz) and fatigue resistant stability (100-105 cycles). This investigation provides a useful reference for developing advanced energy storage ceramics by regulating the doping content and sintering temperature.

Figures of merit of PLZT ferroelectric ceramics for practical applications

Structural, microstructural and pyroelectric properties were investigated in PZT-based ferroelectric ceramics for a composition close to the morphotropic phase boundary (Zr/Ti = 53/47), as a function of the lanthanum content. The samples were prepared via the conventional solid-state reaction sintering method. Three compositions were synthetized and studied following the PbZr0.53Ti0.47O3 + x mole% La nominal formula, where x = 0.0, 2.5 and 5.0. The structural characterization confirmed the presence of both tetragonal and rhombohedral phases for all the studied compositions, showing a decrease in the tetragonality factor (c/a) with the increase of the lanthanum concentration. The observed decrease in the stability of the ferroelectric phase (in favor of the paraelectric one) have been discussed in light of the solubility of the doping cation into the studied PZT perovskite structure. Microstructural properties revealed low pores concentration micrographs, showing homogeneous microstructures and uniform grain-sizes. The pyroelectric response of the as-prepared PLZT samples was also investigated in a wide temperature interval. The lower lanthanum content composition exhibited the best properties, characterized by a high pyroelectric coefficient and enhanced figures of merit. These characteristics make such a composition a promising material for practical applications.

Crystal structures, lattice vibrational characteristics, and dielectric response of Mg3(VO4)2 microwave dielectric ceramics sintered at different temperatures

Mg3(VO4)2 (MVO) microwave dielectric ceramics were fabricated by a conventional solid-state sintering method at different sintering temperatures (Ts) between 1000 °C and 1100 °C. The effects of Ts on the phase evolution, the crystal structures, the dielectric responses, and the lattice vibrational characteristics of MVO were investigated. XRD patterns after Rietveld refinement were applied to analyze the phase evolution and the crystal structures of the samples, which shows the orthorhombic structure with the space group of Cmca for the MVO ceramics. Micrograph from scanning electron microscopy shows a uniform and dense crystal structure with the highest bulk density for the MVO sample sintered at 1050 °C. Raman scattering spectroscopy and infrared reflectance spectroscopy were used to dissect the lattice vibrational characteristics of the MVO ceramics. There are two types of vibrational modes of the MVO samples, i.e., the external modes caused by the deformation of [VO4]3- and the rotational and translational vibrations of the lattices, the internal modes attributed to the asymmetric stretching vibrations of V-O bonds. The intrinsic dielectric properties were determined by fitting the data with a four-parameter semi-quantum (FPSQ) model. Modes 1, 2, and 4, associated with the external modes, have the greatest contribution coefficient of 65.58% to the dielectric constant, and Mode 1 has the greatest contribution coefficient of 51.40% to the dielectric loss. The structure-property relationships were semi-quantitatively mathematically established according to the Raman modes. The MVO sample sintered at 1050 °C has the best dielectric properties of εr = 9.59 and Q × f = 41,193 GHz (f = 13.69 GHz).