The influence of processing methods on the dielectric properties of BaTi1-xGdxO3-x/2 - Based materials

In this study, the intermediate rare-earth oxide Gd₂O₃ (Gd) was substituted in different amounts (x = 0.2–2 mol%) for the formulation of BaTi_1-xGd_xO_3-x/2 (BTG_x) dielectric materials. The effect of B-site substitution was confirmed by the additional Raman active A_1g octahedral peak at ~835cm^-1 strengthened at x ≥ 0.4 mol%. Additionally, properties of 0.9BTG_0.007-0.1BA dielectric ceramics were analysed based on the influence of various processing methods as a function of sintering temperature. The focal samples were labelled Method-A (direct-mix) and Method-B (indirect-mix). As the sintering temperature (1075–1200 °C) increased, the 1 kHz response of the ε–T curves of Method-A samples transformed from a single peak to broad-narrow double peaks of high dielectric loss tangent (tan δ). Nonetheless, samples of Method-B possessed a clearly defined transmission electron microscopy (TEM) core-shell structure, flattened double-peak ε-T curves, optimised dielectric properties (ε = ~1563–1851 and tan δ < 1.5% at room temperature), and a wide-ranging temperature behaviour that meets the X8R dielectric standards (ΔC/C_25°C < ±15%). The maximum dielectric breakdown strength of Method-B samples reached ~131 kVcm, while the energy storage density was ~0.726 J/cm³ at a maximum efficiency of ~80% at 1100 °C. Thus, exhibiting good potentials for balancing temperature stability with energy storage applications.     

Superior temperature‐stable dielectrics for MLCCs based on Bi0.5Na0.5TiO3‐NaNbO3 system modified by CaZrO3

An ultra‐wide temperature stable ceramic system based on (1?x) [0.94(0.75Bi_0.5Na_0.5TiO₃?0.25NaNbO₃)?0.06BaTiO₃]?xCaZrO₃ (CZ100x) is developed for capacitor application in this study. All samples exhibit characteristics of pseudocubic structures in XRD patterns. With CaZrO₃ addition, the coupling effect of polar nanoregions (PNRs) is weakening, leading to greatly improved temperature stability of dielectric properties. Among all samples, the most attractive properties are obtained in the composition of CZ10 at <15% variation in dielectric permittivity spanning from ?55°C to 400°C and lower than 0.02 of dielectric loss of between ?60°C and 300°C, accompanied by high DC resistivity (10⁷ Ω m at 300°C, calculated by fitting Jonscher's power law). Furthermore, tentative multilayer ceramic capacitors (MLCCs) composed of CZ10 dielectric and Ag:Pd (70:30) internal electrode layers were fabricated by tape casting and cofiring processes. Temperature‐stable dielectric property in formation of MLCC was successfully realized, with small ΔC/C_25°C (<15%) and loss factor (≤ 0.02) between ?55°C and 340°C. Meanwhile, CZ10‐based MLCC showed temperature‐insensitive energy storage density of 0.31?0.35 J/cm³ and high‐energy efficiency of above 77% at 120 kV/cm in the range of ?55 to 175°C. All of these exhibit wonderful temperature‐stable dielectric properties and indicate the promising future of CZ10 dielectric as high‐temperature ceramic capacitors.     

Structural,thermal and dielectric properties of 2D layered Ti3C2Tx (MXene) filled poly (ethylene-co-methyl acrylate) (EMA) nanocomposites

Light-weight and flexible 2D MXene-based polymer materials with low dielectric loss and high dielectric constant have drawn great attention in the power systems and modern electronic field. A series of Ti₃C₂T_x/EMA composites were fabricated via simple solution casting followed by a compression molding method with various mass concentrations of Ti₃C₂T_x (0, 1, 3, 5, 8, 10, 12, and 15 wt%). Morphological and micro structural properties of the prepared composites were studied via X-ray diffraction (XRD) and field-emission scanning electron microscope (FESEM), where the distribution of Ti₃C₂T_x in the Ti₃C₂T_x/EMA composites was confirmed. Thermal behaviors were analyzed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) investigations. The DSC analysis reveals that the % of crystallinity decreases from 11.06 with 1 wt% to 5.68 with 15 wt%, where Ti₃C₂T_x acts as an efficient nucleating agent. TGA data confirm the enhancement of the thermal stability of the composites upon increasing in Ti₃C₂T_x loading. The room temperature electrical and dielectric behavior of the studied composites were examined in the frequency range of 100 Hz–5 MHz. In this work, the 10 wt% of Ti₃C₂T_x loaded poly (ethylene-co-methyl acrylate) composite (EMA) showed higher dielectric permittivity (ε′ = 124.22) with lower dissipation loss (tan δ = 0.051) at 100 Hz among all weight percentages. The behavior of charge carriers in the prepared composites was studied by utilizing the impedance spectroscopy technique. The electrical parameters were calculated from the fitted Nyquist plots with a corresponding circuit model. I–V curves confirmed the conduction mechanisms of the composites. This beneficial enhancement in electrical properties recommends the composite can be utilized in flexible electronic storage devices.     

Microstructure effect on dielectric Properties of MgO-doped BaTiO3–BiYO3 ceramics

MgO-doped 0.97BaTiO₃–0.03BiYO₃ (0.97BT–0.03BY) polycrystalline ceramics were prepared by the solid-state sintering method. Then the structural, dielectric and resistant properties were investigated as functions of MgO addition. Microstructure was studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectrometry (EDS). The results show that Bi³⁺, Y³⁺ and Mg²⁺ ions exhibit nonuniform distribution behavior in BT–BY ceramics, demonstrating the existence of a “core–shell” structure, which plays important roles in the capacitance-temperature characteristics, where 0.97BT–0.03BY with the addition 2.2–2.8 at% MgO meets the Electronic Industries Association (EIA) X8R (−55 to 150 °C, ΔC/C_25 °C=±15% or less) specification. Moreover, the fine-grained samples with core–shell structure show much higher bulk resistance than the coarse-grained samples over the studied temperature range, which is attributed to the higher proportion of grain boundaries and the lower concentration of the effective acceptor.     

Structural,electrical, and magnetic properties of Zn substituted magnesium ferrite

Zinc substituted magnesium (Mg–Zn) ferrites with the general formula Mg_1−xZn_xFe₂O₄ (x=0.00, 0.25, 0.50, 0.75, and 1.00) were prepared using the solution combustion route. The dried powder after calcination (700 °C for 2 h) was compacted and sintered at 1050 °C for 3 h. The structural, morphological, dielectric and magnetic properties of the sintered ferrites were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), impedance spectroscopy, and vibration sample magnetometry (VSM). The XRD analysis of sintered samples confirmed that the expected spinel cubic phase was formed for all samples. The crystallite sizes evaluated using Scherre's formula were found to be in the range of 47–80 nm. SEM analysis showed homogeneous grains with a polyhedral structure. The electrical conductivity increased with increasing frequency, which is normal dielectric behavior for such materials. The dielectric constant, dielectric loss tangent, and AC conductivity were found to be lowest for x=0.50. The VSM results showed that the zinc concentration had a significant influence on the saturation magnetization and coercivity.     

Preparation,thermal stability and magnetic properties of new AgY1−xGdx(WO4)2 ceramic materials

Polycrystalline samples of α-AgY_1−xGd_x(WO₄)₂ with x=0, 0.005, 0.01, 0.025, 0.05, 0.1, 0.2, and 1 have been prepared by a solid state reaction method and the influence of Gd³⁺ substitution for Y³⁺ on microstructure, thermal and magnetic properties was investigated. The X-ray diffraction analysis showed the phases to crystallize in the monoclinic symmetry, space group C2/m. A reversible monoclinic to tetragonal phase transition occurs in AgY_1−xGd_x(WO₄)₂ and strongly depends on Gd³⁺ ion concentration. Electron paramagnetic resonance (EPR) spectra of Gd³⁺ ions showed non-monotonous dependence of interaction strength on gadolinium concentration. Magnetic measurements showed paramagnetic behavior and strong increase of magnetic moment as the yttrium content decreases.     

Structural evolution,dielectric and energy storage properties of Na(Nb1−xTax)O3 ceramics prepared by spark plasma sintering

Phase pure NaNb_1−xTaxO₃ ceramics have been successfully prepared by spark plasma sintering (SPS) process at 950–1150 °C. The structural evolution, dielectric and energy storage properties as a function of Ta-doping level were studied by X-ray diffraction (XRD) Rietveld refinement, X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), Raman spectroscopy, scan electron microscopy (SEM) and ferroelectric analyzer. It was found that small level of Ta-doping induced the stabilization of ferroelectric phase from antiferroelectric NaNbO₃, while high level of doping induced further transition from ferroelectric to paraelectric phase. The doping of Ta led to the decrease in Tc and dielectric loss. The NTN4 and NTN6 composition exhibited enhanced dielectric response due to the coexistence of ferroelectric/antiferroelectric or paraelectric phases. The presence of oxygen vacancies in the sintered body were confirmed, which gave rise to the loss at high temperature. The doping of Ta decreased the concentration of oxygen vacancies. Maximum energy density of ∼0.9 J/cm³ could be obtained for x = 0.6 composition with the BDS of ∼160 kV/cm and efficiency of ∼87%.     

Some features of thermophysical properties of γ‐Gd2S3 ceramics based on real structure

The heat capacity C_p, thermal diffusivity χ_T, and lattice thermal conductivity κ_latt of ceramic solid solutions of sesquisulfides Gd_3‐xV_Gd,xS₄ (0 < x < 0.33) in the temperature range 300‐700 K has been studied. Changing the real structure, namely the concentrations of vacancies (N_V) and deformation (N_Dc) centers of polycrystals, significantly decreases κ_latt. A deviation of composition from the stoichiometry 2:3 is accompanied by an increase in the specific area of the crystallite boundaries per unit volume, and, hence, the concentration of deformation centers D_C increases. This observation was confirmed by examining the short‐range order disturbance of the lattice and symmetry environment of the Gd³⁺ and S^2? environment by Raman spectroscopy and the magnetic susceptibility Faraday method. Therefore the thermal diffusivity of gadolinium sesquisulfide is reduced because of the mean free path of phonons decrease. As a result, the thermal conductivity of the polycrystalline samples is reduced by 10%.     

High‐Performance Small‐Amount Fe2O3‐Doped (K,Na)NbO3‐Based Lead‐Free Piezoceramics with Irregular Phase Evolution

[(K_0.43Na_0.57)_0.94Li_0.06][(Nb_0.94Sb_0.06)_0.95Ta_0.05]O₃ + x mol% Fe₂O₃ (KNLNST + x Fe, x = 0~0.60) lead‐free piezoelectric ceramics were prepared by conventional solid‐state reaction processing. The effects of small‐amount Fe₂O₃ doping on the microstructure and electrical properties of the KNLNST ceramics were systematically investigated. With increasing Fe³⁺ content, the orthorhombic‐tetragonal polymorphic phase transition temperature (T_O‐T) of KNLNST + x Fe ceramics presented an obvious “V” type variation trend, and T_O‐T was successfully shifted to near room temperature without changing T_C (T_C = 315°C) via doping Fe₂O₃ around 0.25 mol%. Electrical properties were significantly enhanced due to the coexistence of both orthorhombic and tetragonal ferroelectric phases at room temperature. The ceramics doped with 0.20 mol% Fe₂O₃ possessed optimal piezoelectric and dielectric properties of d₃₃ = 306 pC/N, k_p = 47.0%, = 1483 and tan δ = 0.023. It was revealed that the strong internal stress in the KNLNST + x Fe ceramics with higher Fe³⁺ contents (x = 0.40, 0.60) stabilized the orthorhombic phase, leading to the irregular “V” type rather than the usually observed monotonic phase transition with composition change in the ceramics.     

Effect of Gd3+ and Al3+ on optical and dielectric properties of ZnO nanoparticle prepared by two-step hydrothermal method

Gd³⁺ and Al³⁺ co-doped ZnO nanoparticles were prepared by hydrothermal method. The effects of dopants on the microstructural, morphological, optical and dielectric properties of host ZnO system were investigated in the present report. The microstructural and morphological investigations of all the samples were carried out by X-ray diffraction (XRD) and Field emission scanning electron microscopy (FESEM). To investigate the presence of various intrinsic defects inside the undoped and doped ZnO samples, the Raman spectroscopy and photoluminescence spectroscopy measurements were recorded. The dielectric spectroscopy was carried out as a function of frequency and temperature. The consequences of dielectric measurements suggest that the dielectric response of the 3% Gd³⁺ and Al³⁺ co-doped ZnO sample is significantly enhanced compared to that of undoped ZnO sample. The dielectric response enhances due to the presence of large amount of oxygen vacancies and grain boundaries in the nanostructure of the doped material. All the dielectric parameters confirm the presence of dielectric dispersion inside the doped ZnO samples. The values of dielectric constant as well as ac conductivities were found to decrease at higher concentration of Gd³⁺ and Al³⁺ in the doped ZnO sample and it occurs due to predominating acceptor effect of Al³⁺ at the interstitial site of ZnO nanostructure.     

Role of (La,Gd) co-doping on the enhanced dielectric and magnetic properties of BiFeO3 ceramics

The effect of the La³⁺ and Gd³⁺ co-doping on the structure, electric and magnetic properties of BiFeO₃ (BFO) ceramics are investigated. For the compositions (x=0 and 0≤y≤0.15) in the perovskite structured La_xGd_yBi_1−(x+y)FeO₃ system, a tiny residual phase of Bi₂Fe₄O₉ is noticed. Such a secondary phase is suppressed with the incorporation of ‘La’ content (x). The magnitude of dielectric constant (ε_r) increases progressively by increasing the ‘La’ content from x=0 to 0.15 with a remarkable decrease of dielectric loss. For x=0.15, the system La_xGd_yBi_1−(x+y)FeO₃ exhibits highest remanent magnetization (M_r) of 0.18 emu/g and coercive magnetic field (H_C) of ~1 T in the presence of external magnetic field of 9 T at 300 K. The origin of enhanced dielectric and magnetic properties of La_xGd_yBi_1−(x+y)FeO₃ and the role of doping elements, La³⁺, Gd³⁺ has been discussed.     

Enhanced Curie temperature and superior temperature stability by site selected doping in BCZT based lead-free ceramics

In this work, Bi³⁺ doped Ba_0.98-3x/2Bi_xCa_0.02Zr_0.02Ti_0.976Cu_0.008O₃ [0 ≤ x ≤ 0.03] lead free ceramics, to be employed for structural, dielectric and ferroelectric studies, have been synthesized via conventional solid state reaction method. Rietveld refinement of the X-ray diffraction (XRD) data evidences the existence of a pure perovskite phase with tetragonal symmetry for all ceramics. The Scanning Electron Microscopy (SEM) reveals that the grain size, which is 16.14 μm for x = 0 reduced to 2.11 μm for x = 0.03. Dielectric studies demonstrate excellent dielectric behavior with high Curie temperature (T_C ～159 °C), high dielectric constant (ε_r ～834, ε_max ～ 3146), and a low dielectric loss (tanδ ～ 0.019), for an optimum value of x = 0.02. The analysis of temperature coefficient of the dielectric permittivity indicates the applicability of these materials in multilayer ceramic capacitors. Impedance studies, conducted to understand the underlying physical mechanisms, are found to be in good agreement with the results of structural and dielectric studies. Furthermore, the ferroelectric measurement confirms the ferroelectric nature for all samples with an energy storage efficiency (η) of ～42% for x = 0.02 composition.     

Structures and electrical conductivities of Gd3+ and Fe3+ co-doped cerium oxide electrolytes sintered at low temperature for ILT-SOFCs

Gd³⁺ and Fe³⁺ co-doped cerium oxide electrolytes, Ce_0.9Gd_0.1‐xFe_xO_2-δ (x?=?0.00, 0.01, 0.03, 0.05, 0.07, 0.10), were prepared by co-precipitation for ultrafine precursor powders and sintering for densified ceramic pellets. The crystal and microscopic structures were characterized by XRD, FESEM and Raman spectroscopy and their electrical properties were studied by AC impedance spectroscopy and the measurement of single cell's outputs. In comparison with Ce_0.9Gd_0.1O_1.95, the ceramic pellets of Ce_0.9Gd_0.1‐xFe_xO_2-δ with a relative density of 95% can be obtained after sintered at 1000?°C for 5?h, showing a remarkably enhanced sintering performance with a sintering temperature reduction of 500?°C, which might be ascribed to the highly activated migration of constituent species in the cerium oxide lattice doped with Gd³⁺ and Fe³⁺ions. Moreover, the electrical conductivity of Ce_0.9Gd_0.1‐xFe_xO_2-δ can be significantly enhanced depending on the mole fraction x, with Ce_0.9Gd_0.07Fe_0.03O_1.95 exhibiting the highest electrical conductivity of 38 mS/cm at 800?°C, about 36% higher than that of Ce_0.9Gd_0.1O_1.95 electrolyte sintered at 1500?°C for 5?h. So, The Gd³⁺ and Fe³⁺ co-doped cerium oxide would be an excellent candidate electrolyte for ILT SOFCs due to its prominent sintering performance and enhanced electrical conductivity.     

Enhanced insulation and piezoelectric properties of 0.57(Bi0.8La0.2)FeO3-0.43PbTiO3 solid solutions with Fe addition

0.57(Bi_0.8La_0.2)FeO₃-0.43PbTiO₃-x mol%Fe₂O₃ ceramics (BLF-PT-xFe, x = 0, 0.025, 0.05, 0.125, and 0.25) were prepared by the conventional solid-state reaction method. X-ray diffraction (XRD) reveals that all samples display the perovskite structure with a coexistence of tetragonal (T) phase and rhombohedral (R) phase, while the incorporation of Fe promotes the phase transition from T to R. Scanning electron microscopy (SEM) images show that all samples are well crystallized and their grain size increases noticeably with the increase of Fe content. X-ray photoelectron spectroscopy (XPS) results indicate that Fe doping significantly inhibits the formation of oxygen vacancies, thereby improving insulation of BLF-PT-xFe ceramics. Interestingly, the Curie temperature of BLF-PT-xFe is around 330°C, little changing with the variation of Fe content. However, the depolarization temperatures of BLF-PT ceramics with Fe are 50°C higher than that of the sample without Fe doping. The hopping of second ionized oxygen vacancies are the major carriers in the temperature range of 200°C–500°C. The optimal component of BLF-PT-xFe ceramics appear at x = 0.05, where the dielectric loss tanδ, AC resistivity (200°C), and piezoelectric coefficient d₃₃ could be 0.015, 7 × 10⁶ Ω cm, and 245 pC/N, respectively. All these results indicate that the Fe addition is an effective method to enhance dielectric and piezoelectric properties.     

Remarkable piezoelectricity and stable high‐temperature dielectric properties of quenched BiFeO3–BaTiO3 ceramics

Effects of quenching process on dielectric, ferroelectric, and piezoelectric properties of 0.71BiFeO₃?0.29BaTiO₃ ceramics with Mn modification (BF–BT?xmol%Mn) were investigated. The dielectric, ferroelectric, and piezoelectric properties of BF–BT?xmol%Mn were improved by quenching, especially to the BF–BT?0.3 mol%Mn ceramics. The dielectric loss tanδ of quenched BF–BT?0.3 mol%Mn ceramics was only 0.28 at 500°C, which was half of the slow cooling one. Meanwhile, the remnant polarization P_r of quenched BF–BT?0.3 mol%Mn ceramics increased to 21 μC/cm². It was notable that the piezoelectric constant d₃₃ of quenched BF–BT?0.3 mol%Mn ceramics reached up to 191 pC/N, while the T_C was 530°C, showing excellent compatible properties. The BF–BT?xmol%Mn system ceramics showed to obey the Rayleigh law within suitable field regions. The Rayleigh law results indicated that the extrinsic contributions to the dielectric and piezoelectric responses of quenched BF–BT?xmol%Mn ceramics were larger than the unquenched ceramics. These results presented that the quenched BF–BT?xmol%Mn ceramics were promising candidates for high‐temperature piezoelectric devices.     

The role of Pb and annealing temperature on the structural,magnetic, optical and dielectric properties of W-type hexaferrite nanostructures

In this paper, W-type Sr_1-xPb_xCo₂Fe₁₆O₂₇ nanostructures were synthesized by auto-combustion sol-gel method. Then, the effects of annealing temperature and Pb contents on the structural, magnetic, optical, and dielectric properties of Sr_1-xPb_xCo₂Fe₁₆O₂₇ nanostructure were investigated. First, a gel of metal nitrates with a specific molar ratio with x different was prepared and then the gel was annealed at different temperatures for 4?h. To determine the annealing temperature of the samples, the prepared gel was examined by thermogravimetric analysis and differential thermal analysis. The morphology and crystal structure of the prepared samples were characterized by field emission scanning electron microscopy (FESEM) and X-ray diffraction pattern (XRD). The results of XRD patterns indicated that the annealing temperature of synthesized Sr_1-xPb_xCo₂Fe₁₆O₂₇ was reduced by increasing Pb contents. In addition, FESEM images showed that the microstructure of the samples was homogeneous and uniform, but since the samples have a magnetic property, the particles were aggregated. Fourier transform infrared analysis (FT-IR) was used to confirm the phase formation. The FT-IR results of the samples indicated that the tetrahedral and octahedral sites, which are the important attributes of hexaferrites, were formed. The magnetic properties of the samples were measured by vibrating sample magnetometer (VSM). The VSM results of the samples showed that because of increasing Pb content, the amount of saturation magnetization and that of magnetic coercivity decreased from 81.29 to 10.23?emu/g and 2285–477?Oe, respectively. The optical properties of the samples were investigated by ultraviolet–visible spectroscopy, which revealed that the energy gap decreases and the absorption peaks move towards longer wavelengths by increasing Pb content. The dielectric properties of the samples were investigated by the LCR meter. It was found that by increasing frequency, the dielectric constant (ε^′) and the dielectric loss (?) of the samples were decreased.     

Broadband electromagnetic absorption of Ti3C2Tx MXene/WS2 composite via constructing two-dimensional heterostructure

Ti₃C₂T_x MXene, an emerging two-dimensional (2D) ceramic material, has rich interfaces and strong conductive networks. Herein, we have successfully built a heterostructure between Ti₃C₂T_x MXene and WS₂ to improve electromagnetic absorption performance. X-ray diffraction and X-ray photoelectron spectroscopy were used to determine the successful synthesis of Ti₃C₂T_x/WS₂ composite. Field emission scanning electron microscopy and transmission electron microscopy images show that WS₂ nanosheets are evenly dispersed on the accordion-like Ti₃C₂T_x MXene. Importantly, Ti₃C₂T_x MXene/WS₂ composite has sufficiently high dielectric loss and impedance matching due to self-adjusting conductivity and 2D heterostructure interfaces. As a result, the Ti₃C₂T_x/WS₂ composite has a minimum reflection loss (RL_min) of −61.06 dB at 13.28 GHz. Besides, it has a broad effective absorption bandwidth (EAB) of 6.5 GHz, with EAB >5.0 GHz covering a wide range of thickness. Such impressive results may provide experience for the application of Ti₃C₂T_x ceramics and 2D materials.     

Effect of neodymium ion on the structural,electrical and magnetic properties of nanocrystalline nickel ferrites

NiNd_xFe_2-xO₄ nanoferrites with different compositions of x?=?0.01, 0.03, 0.05, 0.07 and 0.09 were prepared using the sonochemical method. The structural, optical and morphological properties of the prepared nanoferrites were characterized by X-ray diffraction, ultra violet-diffuse reflectance spectroscopy, scanning electron microscopy and X-ray fluorescence techniques. The X-ray diffraction analysis of the prepared nanoferrites confirmed the presence of a cubic spinel structure. The average crystallite sizes of the prepared nanoferrites were 52, 49, 46, 44 and 40?nm for x?=?0.01, 0.03, 0.05, 0.07 and 0.09, respectively. The particle size of the prepared NiNd_xFe_2-xO₄ nanoferrites was in the range 60–40?nm. The dielectric parameters ranged from 2.9?GHz to 5.6?GHz. Decrease in the dielectric constant was observed with an increase in Nd³⁺ ions in the prepared NiNd_xFe_2-xO₄ nanoferrites. However, a reverse trend was observed in the dielectric loss. An impedance analysis of the prepared nanoferrites was carried out to explore the pseudo-capacitance behavior. The saturation magnetization and remnant magnetization values of the prepared nanoferrites decreased with an increase in the concentration of Nd³⁺ ions in NiNd_xFe_2-xO₄ nanoferrites.     

New Antiferroelectric Solid Solution of Pb(Mg1/2W1/2)O3–Pb(Zn1/2W1/2)O3 as Dielectric Ceramics

A new solid solution of (1?x)Pb(Mg_1/2W_1/2)O₃–xPb(Zn_1/2W_1/2)O₃ has been prepared in the form of ceramics by solid‐state reaction with composition x up to 30%. It is found that with the substitution of Zn²⁺ for Mg²⁺ on the B site of the of complex perovskite structure the antiferroelectric (AFE) Curie temperature T_C of PMW increases from 40°C (x = 0) to 67°C (x = 30%), indicating an enhancement of antiferroelectric order, whereas, at the same time, the phase transition becomes more diffuse due to a higher degree of chemical inhomogeneity. X‐ray diffraction analysis indicates that the crystal structure adopts an orthorhombic space group (Pmcn) with a decrease in lattice parameter a, but an increase in b and c as the Zn²⁺ concentration increases. The low dielectric constant (~ 10²), low dielectric loss (tanδ ≈ 10^?3), linear‐field‐induced polarization, and significantly high breakdown field (~ 125 kV/cm) at room temperature make this family of dielectric materials a promising candidate for ceramic insulators.     

Structural and thermoelectric properties of GdxSr2-xCoO4 layered perovskites

Gd_xSr_2-xCoO₄-layered perovskites with varying gadolinium content (x = 0.5, 0.6, 0.7, 0.8, 0.9, 1.0) were synthesised using a conventional solid-state reaction method in air. X-ray diffraction (XRD) analysis indicated that all samples were single phase with a tetragonal I4/mmm K₂NiF₄-type structure. Rietveld refinements showed that the lattice parameters and the in-plane Co–O bond length decreased with increasing Gd³⁺ content, suggesting stronger structural distortion. The X-ray photoelectron spectroscopy (XPS) analysis indicated that cobalt ions on the surface of Gd_xSr_2-xCoO₄ had Co³⁺ and Co⁴⁺mixed valence states and many oxygen vacancies. The thermoelectric properties of Gd_xSr_2-xCoO₄ (x = 0.7, 0.8) were also investigated. The temperature dependencies of the electrical conductivity (σ) and Seebeck coefficient (S) up to 750 °C for Gd_0.7Sr_1.3CoO₄ showed maximum and minimum values at approximately 550 °C. Below 550 °C with increasing Gd³⁺ content, S increased, whereas σ and the thermal conductivity (κ) decreased, leading to an increase in the figure of merit (ZT). A maximum ZT value of 0.0039 for Gd_0.8Sr_1.2CoO₄ was obtained at 400 °C. The variations of σ, S and κ with x and temperature are discussed.