Solid-state Reaction Sintering Research Articles

Strontium tantalate ceramics for dielectric resonator and antenna applications

Bulk SrTa2O6 ceramics were produced via solid-state reactive sintering, characterized by x-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy, and their dielectric properties determined via resonant cavity in the 5G frequency domain. Two polymorphs were obtained. Orthogonal β phase ceramics, obtaining much lower relative densities, achieved, at ∼5 GHz, an effective permittivity (εeff) of ∼22, dielectric losses (tanδ) around 1 × 10−2 and temperature coefficient of resonant frequency (τf) of around 250 ppm/°. Tetragonal tungsten bronze β’ phase ceramics achieved relative densities of ∼87%, and at ∼2.8 GHz a higher εeff between 79-85, lower ‘tanδ’ around 5 × 10−3, and a ‘τf’ of about 300 ppm/° at 90°C. Both phases are found to be Sr-deficient, which may have caused a liquid-phase sintering in the powder bed configuration used for these ceramics. The performance of a prototype dielectric resonator antenna incorporating a β’ ceramic was demonstrated to validate the measured dielectric properties.

High electrical conductivity and enhanced thermoelectric properties in La-Nb co-doped (Sr1/3Ba1/3Ca1/3)TiO3-based oxides

Here, we report a series of (Sr1/3Ba1/3Ca1/3)TiO3-based oxides with different La-Nb doping levels synthesized by solid-state reaction and graphite-burial sintering method. The results indicate that La-Nb co-doping significantly enhances the electrical conductivity by increasing carrier concentration, leading to a remarkable improvement in power factor (∼1665 μW/(m·K2) at 773 K). Additionally, the lattice thermal conductivity is reduced due to the enhanced phonon scattering caused by point defects and pores. As a result, a peak ZT value of 0.36 at 773 K is achieved for the 5% La-10% Nb co-doped sample, 200% higher compared to the un-doped sample. This work highlights the promising potential of the (Sr1/3Ba1/3Ca1/3)TiO3-based oxides as environmentally-friendly thermoelectric materials.

The effect of dual-sites high-entropy strategy on thermal conductivity of pyrochlore ceramics

The emergence of high-entropy materials has developed a new strategy for the design and optimization of ceramics with desired properties. In this work, the (Gd1/7La1/7Nd1/7Sm1/7Eu1/7Dy1/7Ho1/7)2(Ti1/4Zr1/4Sn1/4Hf1/4)2O7 pyrochlore ceramic with dual-sites high-entropy design has been successfully prepared by a solid-state reaction sintering method. The samples possess a single-phase of pyrochlore structure, and all introduced elements are distributed homogeneously at A and B sites, respectively. Based on the synergistic high-entropy design of A and B sites, the thermal conductivity value of high-entropy pyrochlore ceramic could be diminished to 1.37 W∙m−1∙K−1.

Enhanced thermoelectric properties of Mg2Si0.3Sn0.7 via Bi-doping under high pressure

A series of n-type Mg2(Si0.3Sn0.7)1-xBix compounds with 0≤x≤0.02 were successfully synthesized through a combined approach involving solid-state reaction, high-pressure synthesis, and spark plasma sintering techniques. The method yielded homogeneously distributed single-phase materials at the micron scale, although minor compositional variations were detected within nanoscale precipitates embedded in the grains. The sample with Bi content of 0.01 exhibited enhanced thermoelectric properties, reaching a peak thermoelectric figure of merit (ZT) of 1.45 at 700 K while maintaining an average ZT of about 1.1 over the temperature range of 300−773 K. The enhancement in thermoelectric performance is ascribed to the optimized carrier concentration, band convergence, and refined microstructure. The findings suggest a simplified approach to doping that could be beneficial in creating high-performance thermoelectric materials for energy conversion.

Research electrical properties of Cu doped FeTe2 prepared by solid state reaction

The present study successfully prepared CuxFeTe2 (x=0.01, 0.05, 0.1, 0.15, and 0.2) compounds using a high-temperature solid state reaction sintering technique under preparation conditions ranging from 623 K to 823 K. The phase structure and microstructure of CuxFeTe2 were determined using X-ray diffraction and scanning electron microscopy. Simultaneously, we studied the Seebeck coefficient and electrical resistivity of the sample. It was found that the samples prepared at 673 K had a purer phase, and the thermal power coefficient was better for samples with a Cu doping concentration below 0.1.

Lithium Dendrite Propagation in Ta-Doped Li7La3Zr2O12 (LLZTO): Comparison of Reactively Sintered Pyrochlore-to-Garnet vs LLZTO by Solid-State Reaction and Conventional Sintering.

Ta-doped Li7La3Zr2O12 (LLZTO) garnet is a promising Li-ion-conducting ceramic electrolyte for solid-state batteries. However, it is still challenging to use LLZTO in Li metal batteries operating at high current densities because of the tendency for Li metal to nucleate and propagate along the grain boundaries. In this study, we carry out a detailed investigation to elucidate the effect of microstructure and grain size on the electrochemical properties and short circuit behavior in LLZTO. Pellets were prepared using reactive sintering from pyrochlore precursors (a method called pyrochlore-to-garnet, P2G) and compared with LLZTO synthesized using solid-state reaction (SSR) followed by conventional pressureless sintering. Both preparation methods were controlled to keep the phase and elemental composition, ionic and electronic conductivity, relative density, and area-specific resistance of the pellets constant. Reflection electron energy loss spectroscopy and X-ray photoelectron spectroscopy confirm that both types of LLZTO have similar band gaps and chemical states. Microstructure analysis shows that the P2G method results in LLZTO with an average grain size of around 3 μm, which is much smaller than the grain sizes (as large as 20 μm) seen in SSR LLZTO. Galvanostatic Li stripping/plating and linear sweep voltammetry measurements show that P2G LLZTO can withstand higher critical current densities (up to 0.4 mA/cm2 in bidirectional cycling and >1 mA/cm2 for unidirectional) than those seen in SSR LLZTO. Post-mortem examination reveals much less Li deposition along the grain boundaries of P2G LLZTO, particularly in the bulk of the pellet, compared to SSR LLZTO after cycling. The improved cycling behavior in P2G LLZTO despite the higher grain boundary area could be from more homogeneous current density at the interfaces and different grain boundary properties arising from the liquid-phase, reactive sintering method. These results suggest that the effect of grain size on Li dendrite propagation in LLZO may be highly dependent on the synthesis and sintering method employed.

Photostriction in CaTiO3 ceramics under the illumination of a light emitting diode

CaTiO3 ceramic, prepared by solid state reaction and spark plasma sintering, is investigated for a significant photostriction in the illumination of a light emitting diode.

Positive effect of co-addition of Dy2O3/Ag and Dy2O3/WO3 nanoparticles on the physical critical parameters and electrical transport properties of YBCO ceramic

In this study, YBa2Cu3O7−δ (YBCO) polycrystalline samples with co-addition of nanostructure materials (NSMs) of 0.1 wt% Dy2O3/Ag and 0.1 wt% Dy2O3/WO3 were synthesized via solid-state reaction sintering. Herein, the considered NSMs are of two shapes: nanoparticles (NPs) of dysprosium oxide and silver and nanowires of tungsten oxide. X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) were used to examine the structure and morphology of samples. Resistivity versus temperature (ρ(T)), ac susceptibility (χ(T)), and dc magnetization (M(H)) measurements have been carried out on superconducting YBCO to deduce critical superconducting parameters like Bc1 and Jc. Using the Aslamazov-Larkin approach, the induced excess conductivity analysis was performed to complete values of critical lengths such as ξco, λo, critical magnetic fields (Bc1, Bc2), and critical current density Jc at 0 K. The combined addition of Dy2O3/Ag and Dy2O3/WO3 conserves the orthorhombic structure, the grain size of about some micrometers, and the volume fraction of superconductor grain (Vsg%). NSMs co-addition ameliorates the assembly of grains and their connectivity to empower the carriers' charge transportation between the grains. Dy-rich entities are inserted into the YBCO grains' surfaces. The critical superconducting parameters Bco, Bc1, Bc2, and Jc are high in co-added samples due to the decrease in intergrain resistivity and the better competence of trapping flux lines inside the samples. The combination of different types of NSMs inside YBCO constitutes a hopeful way to compromise between better grain coupling and higher flux pinning. AgNPs coupled with Dy2O3NPs act more efficiently than WO3NW coupled with Dy2O3NPs in YBCO compounds to make its properties better.

Effect of TEOS content on microstructure evolution and optical properties of Sm:YAG transparent ceramics

Highly transparent 4.5 at.% Sm:YAG ceramics were fabricated by solid-state reactive sintering using tetraethyl orthosilicate (TEOS) and CaO as sintering additives. The influences of TEOS content on phase formation, microstructure evolution, and optical properties were investigated. The 4.5 at.% Sm:YAG ceramics with 0.3–0.6 wt% TEOS all have a single yttrium aluminum garnet phase after pre-sintering at 1725 °C for 30 h. With TEOS increasing from 0.3 to 0.6 wt%, residual pores were gradually discharged, the Sm:YAG ceramics with 0.5 and 0.6 wt% TEOS showed fully dense microstructure after vacuum sintering at 1725 °C for 30 h. After hot isostatic pressing (HIP) at 1750 °C for 3 h, the average grain size of the final Sm:YAG ceramics increased from 9.5 to 15.8 μm with TEOS increasing from 0.3 to 0.6 wt%, and all the ceramic samples showed uniform microstructures. The 4.5 at.% Sm:YAG ceramics with 0.6 wt% TEOS achieved high in-line transmittance of 83.6% at 808 nm and absorption coefficient of 3.32 cm−1 at 1064 nm, which means it can effectively suppress amplified spontaneous emission and parasitic oscillation.

Luminescent Properties of (Ca7ZrAl6O18-Ca3Al2O6-CaZrO3):Eu3+ Composite Ceramics and Tracing in the Hydration Process

In this work, solid-state reaction sintering was used to fabricate Ca7ZrAl6O18-Ca3Al2O6-CaZrO3:Eu3+ ternary composite ceramics and cements. The structural, microstructural, and spectroscopic properties of the ceramics with different Eu2O3 content were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), and spectrofluorimetry, respectively. The XRD patterns analyzed with Rietveld refinement confirm the presence of the orthorhombic phase of Ca7ZrAl6O18 and the cubic phase of Ca3Al2O6 in all the samples, indicating that doping of Eu3+ slightly changes the crystalline structure of both aluminate phosphors. EDS analysis revealed that the Eu doping element was strongly concentrated to the two phases, i.e., Ca7ZrAl6O18 and Ca3Al2O6, with the Eu concentrations of 8.45 wt.% and 8.26 wt.%, respectively. The luminescent properties of the ceramics doped with different Eu3+ ion concentrations were investigated by excitation and emission spectroscopy at room temperature. These results were compiled using a laser with an optical parametric oscillator (OPO) system. The obtained spectra indicated changes in the luminescence intensity and shape occurring with phase composition and Eu2O3 concentration. The emission spectra of the ceramics exhibit a strong dependence on the excitation wavelength in the range from 210 to 300 nm, and invariably, five peaks were assigned to the 5D0 → 7FJ (J = 0, 1, 2, 3, 4) transitions of Eu3+. The luminescence spectroscopy was then used to trace the early and long-term hydration behavior of cements. Thus, luminescence spectroscopy may provide a new tool for non-destructive testing of cement-based structures.

Microstructure evolution of porous calcium hexaluminate compacts during first heating

Porous calcium hexaluminate (CaAl12O19 or CA6) structures show long-term stability at high temperatures, high refractoriness, low thermal conductivity, and excellent chemical resistance, thus being Taylor-made for thermal insulation. Previous works attained porous structures from in situ formation of CA6 combining CaO and Al2O3 sources in solid-state reactive sintering. Although the approach is time-and-energy-saving regarding the production of large parts of complex shapes, it faces considerable difficulties related to the expansive formation of calcium aluminates. To overcome such drawbacks, pre-formed porous CA6 aggregates improve the system's dimensional stability before sintering. Despite the straightforward processing, few studies have investigated such materials systemically. This article addresses the combination of pre-formed porous CA6 aggregates and organic and inorganic binders for the production of porous structures by two shaping processes, namely, uniaxial pressing and direct casting of aqueous suspensions. After drying, the samples' microstructure and physical properties evolution were investigated up to sintering (1100-1500 °C) through total porosity, Young's modulus, compression strength, pore diameter, and thermal conductivity measurements, dilatometric analyses, and scanning electron microscopy. Reference samples of coarse calcined alumina were tested under the same conditions to highlight the impacts of CA6 particles' morphology. Compared to them, the CA6-containing samples showed almost no variation in total porosity and average pore size levels during thermal treatments, although their strength and rigidity increased significantly after sintering. Their microstructure remained practically unchanged after drying, showing clusters of large asymmetrical CA6 crystals bonded to each other by their edges, and surrounding a large fraction of 1.8–2.2 μm pores. According to the results, although water content, processing method, and compacting levels are important parameters, particles' microstructure, ratio of intra-particle pores, and asymmetrical shape are key variables for the development of physical properties. Such characteristics strongly contributed to their densification resistance and lower thermal conductivity after exposure to high temperatures.

Medium-entropy (Sr1/3Ba1/3Ca1/3)TiO3 perovskite oxide for thermoelectric applications

A novel ternary medium-entropy perovskite oxide, (Sr1/3Ba1/3Ca1/3)TiO3, is reported for thermoelectric applications; it was synthesized via solid-state reaction and graphite burial sintering. The formation and stability of the single-phase structure were evaluated using thermodynamic calculations and the Goldschmidt’s tolerance factor. The material was found to have a single-phase cubic perovskite structure with a homogeneous distribution of all elements. The medium entropy generates moderate carrier mobility, while the band flattening yields high Seebeck coefficient, resulting in a high power factor of 378.8 μW·m−1·K−2 at 773 K. The enhanced multi-phonon scattering derived from the medium entropy, oxygen vacancies, and porous structure significantly reduced the lattice thermal conductivity, with a lowest value of 1.90 W·m−1·K−1 at 773 K. As a result, a ZTmax of 0.13 was attained at 773 K, which outperforms that of high-entropy SrTiO3-based oxides. This work provides a new direction to obtain high-performance thermoelectric materials through medium-entropy composition design.

Enhanced ferroelectric and magnetic properties of the 0–3 type BiFeO3-BaTiO3/BaFe12O19 composite multiferroic material

The 0–3 type (1-x)(0.75BiFeO3-0.25BaTiO3)/xBaFe12O19 (BFO-BTO/BaM) multiferroic composites were successfully prepared by a solid-state reaction sintering process. The coexistence of perovskite BFO-BTO phase and hexagonal BaM phase was confirmed for all BFO-BTO/BaM composites. Due to the large leakage current, the breakdown electric field decreased with increasing BaM content. Nevertheless, the ferroelectric properties of the composite ceramics have also been significantly improved, mainly as the increase of remanent polarization and the decrease of coercive field, where Pr = 19.79 μC/cm2, Ec = 30 kV/cm at x = 0.075. Meanwhile, the magnetic properties of BFO-BTO phase were enhanced, and the remanent magnetization linearly increased with increasing BaM content. The single domain magnetic structure was obtained for all BFO-BTO/BaM composite ceramics, and the magnetic properties changed after electric poling, which indicated the electric field controlled magnetic properties. The electric-controlled magnetic behavior was attributed to the structural phase transition. The magnetoelectric coupling coefficient αME of the composite material has been improved, with a maximum value of 0.61 mV/cm.Oe. Thus, the BFO-BTO/BaM magneto-electric composite system is a promising multiferroic system in information technology and sensing fields.

Corrosion behavior of CMAS-infiltrated Ba(Mg1/3Ta2/3)O3 ceramic based on material characteristics

Calcium–magnesium–alumina–silicate (CMAS) corrosion is inevitable in thermal barrier coating applications. Herein, Ba(Mg1/3Ta2/3)O3 (BMT) ceramic, which is a promising thermal barrier coating material, was prepared using a solid-state reaction sintering method. The effects of the surface roughness and bulk density on the CMAS corrosion behavior of BMT ceramic were analyzed by investigating the surface morphology, cross-sectional microstructure, compositional evolution, and CMAS wetting behavior before and after CMAS corrosion. The results indicate that the wettability of CMAS on the BMT bulk material with a low surface roughness was lower than that of the material with a high surface roughness owing to the smaller driving capillary force, actual contact area between CMAS and the surface, and CMAS infiltration direction in BMT with a low surface roughness. This effectively inhibited the infiltration of CMAS and reduced its corrosion effect on BMT ceramic. The infiltration of CMAS into the BMT bulk materials with a high density was weaker because there were few channels, such as pores and microcracks, for infiltration. Therefore, reducing the surface roughness and increasing the density of BMT ceramic can be considered an effective method for improving its CMAS corrosion resistance.

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.

Ce/Mn/Cr: (Re,Y)3Al5O12 Phosphor Ceramics (Re = Gd, Tb and Lu) for White LED Lighting with Significant Spectral Redshift and Improved Color-Rendering Index.

In order to attain phosphor ceramics with a high Color-Rendering Index (CRI), samples with the composition of Y0.997-xRexCe0.003)3(Al0.9748 Mn2+0.024Cr3+0.0012)5O12(Rex = 0, Gd0.333, Gd0.666, Gd0.997, Tb0.333, Tb0.666, Tb0.997 and Lu0.997 were prepared by solid-state reaction and vacuum sintering, and exhibited potential for high-quality, solid-state lighting. Doping with Cr3+ and Mn2+ effectively enhanced the red component of Ce3+ spectra through the intense energy transfer from Ce3+ ions to Mn2+/Cr3+ ions. The crystal field splitting of [GdO8] and [TbO8] was more extensive than that of [YO8], causing a massive redshift in the Ce3+ emission peaks from 542 to 561 and 595 nm, while [LuO8] had an opposite effect and caused a blueshift with a peak position at 512 nm. White LED devices incorporating Ce/Mn/Cr: (Gd0.333Y0.664)3Al5O12 phosphor ceramic exhibited a high CRI of 83.97, highlighting the potential for enhancing the red-light component of white LED lighting.

Thermoelectric and mechanical properties of Bi0.42Sb1.58Te3/SnO2 bulk composites with controllable ZT peak for power generation

Bi2Te3-based materials' potential for power generation at lower to moderate temperatures is curtailed by intrinsic excitation. This study seeks to address this issue. This is accomplished by fabricating bulk thermoelectric materials consisting of varying weights of SnO2 via solid-state reaction and spark plasma sintering. Results show that the composite material has an average ZT value of ∼0.85 in the 425–575 K temperature range. The lattice thermal conductivity of the composite material is reduced by approximately 54% compared to pure Bi0.42Sb1.58Te3 (BST) and almost 47% when compared to Cu1.8S modified- Bi0.42Sb1.58Te3 (m-BST) at 300 K. A high power factor is achieved, which almost doubled in the 425–575 K. The composite material also exhibits significantly enhanced hardness and modulus due to compositing. These findings provide a straightforward strategy for improving the low- to medium-temperature thermoelectric performance of commercial p-type (BiSb)2Te3, which is crucial for expanding the temperature range of Bi2Te3-based materials.

Low frequency dielectric dispersion in the AgNbO3 ferroelectric ceramic system

Lead-free AgNbO3 ceramic system has been synthesized via solid-state reaction sintering method. High-density material has been obtained, revealing the formation of the pure perovskite structure, without secondary phases. Dielectric response showed three typical anomalies in the temperature dependence of the dielectric permittivity, with evident frequency-dependent dielectric dispersion for temperatures close to both the room temperature and the Curie temperature regions. Results have been analyzed and discussed within the framework of the theoretical models reported in the literature.

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.

Fast pressureless solid-state reaction sintering of highly infrared transparent MgAlON ceramics from MgAl2O4 and AlON powders by two-step heating

Fast pressureless solid-state reaction sintering of highly infrared transparent MgAlON ceramics from MgAl2O4 and AlON powders by two-step heating