Reactive Sintering Method Research Articles

Excellent Energy Storage and Charge-Discharge Performance in (Pb1-xCax)(Zr0.55Sn0.45)O3 Antiferroelectric Ceramics.

Lead-based antiferroelectric (AFE) ceramics have the advantages of high power density, fast charge and discharge speed, and the electric-field-induced AFE-FE phase transition, making them one of the potential dielectric energy storage materials. However, the energy storage density still needs to be improved. In this work, (Pb1-xCax) (Zr0.55Sn0.45)O3 (PCZS, x = 0.01, 0.02, 0.03 and 0.04) antiferroelectric ceramics were successfully prepared using the solid-state reaction and two-step sintering methods. The results showed that as the Ca2+ content increased, the average grain size decreased from 1.38 ± 0.42 to 1.06 ± 0.35 μm and the dielectric breakdown strength increased from 270 to 325 kV/cm for ceramics with 80 μm in thickness. Two kinds of superlattice structures (F-point with 1/2{ooo} patterns and incommensurate modulation structure (IMS) pattern with 1/n{110} patterns) were observed, indicating the typical octahedral tilting-related AFE structure. The (Pb0.98Ca0.02) (Zr0.55Sn0.45)O3 bulk ceramics, due to the refined polarization-electric field hysteresis loop of the IMS, achieved a maximum recoverable energy storage density (Wrec) of 6.61 J/cm3 with an efficiency (η) of 84.01%. In the circuit of charge-discharge to a load, an ultrahigh power density (PD) of 276.67 MW/cm3 and a discharged energy density (Wdis) of 6.24 J/cm3 were obtained in PCZS2 bulk ceramics at 290 kV/cm. The high Wrec and Wdis indicate that PCZS ceramics offer potential applications in the field of pulse-power electric devices.

Microstructure and mechanical properties of W-HfC alloy synthesized by in-situ fabrication via pressureless sintering

The materials, primarily utilized in the manufacturing process, significantly impact the microstructure and mechanical properties of W-HfC alloys. In this study, different initial composition, such as HfH2/WC, HfH2/C and HfC, were respectively mixed into W powders, three categories of W-HfC alloys (abbreviated as WHC1, WHC2 and WHC3 successively) were fabricated by in-situ reaction sintering methods. The microstructure and mechanical properties of three alloys were investigated comparatively by using X-ray diffraction, electron microscopy and high temperature tensile tests. The results revealed that WHC2 alloy presents an exceptional ductile-brittle transition temperature of ∼300 °C and the best comprehensive performance. Tensile testing at 300 °C indicates that WHC2 alloy exhibits a complete plastic fracture curve with a tensile strength of 400 MPa and a residual deformation of 9 %, as well as the plasticity enhancement. It is mainly attributable to the dispersion strengthening effect of second phase particles at grain boundaries and within W-matrix grains. Furthermore, the excellent overall performance of the WHC2 alloy demonstrates that the in-situ reaction can significantly reduce sintering difficulties, while the resultant second phase particles provide considerable advantages in improving the properties of W-based alloys. These findings provide valuable insights into the synthesis process and mechanical performance of W-HfC alloys, enabling advancements in their application in high-temperature environments.

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.

Reactive Sintering of Garnet Type LLZTO from Pyrochlore Synthesized Using a Nonaqueous Sol-Gel Method

Garnet-type solid-state electrolytes such as Li7La3Zr2O12 (LLZO) are promising ceramic electrolytes for all-solid-state batteries because of their high (electro)chemical stability and ionic conductivity. LLZO is typically synthesized from oxide precursors via solid-state reaction, but use of other precursors can lead to improved phase purity and homogenous dopant distribution. We recently demonstrated that pyrochlores synthesized using molten salt synthesis can serve as starting precursor for LLZO, a process we call “pyrochlore-to-garnet” (P2G) [1]. Here, a new, scalable synthesis method for multi-doped pyrochlore is demonstrated using non-aqueous sol-gel methods [2]. The P2G method provides an alternative way to prepare dense LLZO material with greatly reduced sintering time and different microstructure properties compared to other methods. For Ta-doped LLZO (LLZTO), the dense LLZTO ceramic is directly obtained via reactive sintering of the multi-doped pyrochlore with a lithium salt and displays high relative density and ionic conductivity 0.4-0.7 mS/cm, which is comparable to LLZTO prepared by solid-state reaction (SSR), using only 2 hours sintering at 1100 degrees Celsius. Investigation of the synthesis parameters shows that liquid phase sintering is important for achieving high pellet densities and phase-purity in the P2G process. Microstructure analysis also shows that the P2G method results in LLZTO with average grain size of around 3 µm, which is much smaller than the grain sizes (as large as 20 µm) seen in SSR LLZTO. The P2G method also allows for preparation of cubic phase LLZO with other dopants using similar conditions. The P2G method is also applied to prepare other kinds of garnets that display mixed ionic and electronic conductivity, such as Ga and Cr doped Li7Pr3Zr2O12.To better understand the effects of microstructure and grain size on the lithium dendrite propagation behavior, a detailed investigation was carried out on LLZTO prepared with the P2G process and conventional SSR followed by conventional pressureless sintering [3]. 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 (REELS) and X-ray photoelectron spectroscopy (XPS) confirmed that both types of LLZTO have similar bandgaps and chemical states. 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. Postmortem 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 homogenous current density at the interfaces and different grain boundary properties arising from the liquid-phase, reactive sintering method. This work shows the P2G is a promising and versatile alternate method for the synthesis and processing of many kinds of LLZO materials.

The influence of CeO2 on the oxidation resistance of TaC/Ni composites

The in-situ TaC/Ni composites with different CeO2 content (0 wt%, 1 wt%, 2 wt%) were prepared by reactive sintering method, and their oxidation behavior in air at 1073 K was analyzed by static cyclic oxidation method to investigate the influence mechanism of CeO2 on the oxidation resistance of composites. The results show that the CeO2 particles are distributed around the TaC particles in the Ni matrix, and the oxidation behavior of composites with different CeO2 content conforms to the linear kinetic law. The oxide film is mainly composed of NiTa2O6 and a small amount of NiO. The generation reactions of Ta2O5 and NiTa2O6 induce a high expansion and compressive stress in oxide scale, leading to the formation of nonprotective oxide film with pores and cracks on the surface. As the addition of CeO2 increases from 0 wt% to 2 wt%, the thickness of oxide scale on composites obviously reduces from 505 μm to 122 μm, and the Ni and Ta oxides content decreases, leading to the reduction of pores and cracks in oxide scale. The Ce ion generated from the dissolution of CeO2 particles mainly distributes in the Ta oxides during the oxidation process, which hinders the outward diffusion of Ni and Ta ions, resulted in the improved oxidation resistance of TaC/Ni composites.

Effect of Cr content on the high temperature oxidation behavior of FeCoNiMnCrx porous high-entropy alloys

FeCoNiMnCr porous high-entropy alloys were prepared using the activation reaction sintering method with Fe, Co, Ni, Mn, and Cr as raw materials. The oxidation behaviors of FeCoNiMnCrx porous high-entropy alloys with different Cr contents, such as pore structure, the surface oxide film phase composition, structure, and morphology, were characterized by X-ray diffraction (XRD), electron probe micro analysis (EPMA), energy dispersive X-ray spectroscopy (EDS), and pore tester after high-temperature oxidation at 800–1000 °C. The results indicate that the initial porous high-entropy alloy comprises a single FCC solid solution phase. With the increase in Cr content, the average pore diameter, average porosity, and air permeability of the porous high-entropy alloy also increase. The oxidation kinetics of the porous high-entropy alloy after exposure to temperatures between 800 °C and 1000 °C follows a single-stage parabolic evolution law. At the same oxidation temperature, With the increase of Cr content, the oxidation gains gradually increased, at the same Cr content at different temperatures, the antioxidant performance of 1000 °C was the weakest, followed by 800 °C, and 900 °C showed excellent antioxidant performance. The oxidation products are mainly Mn2O3, Mn3O4, (Mn, Cr)3O4, Cr2O3and Fe2O3.

Preparation of porous (Mo2/3Y1/3)2AlC and its hydrogen evolution reaction performance

Porous (Mo2/3Y1/3)2AlC MAX phase ceramic was prepared by reaction sintering method using Mo, Y, Al, and graphite powder as raw materials. The influence of changes in Al content on the purity of the obtained samples was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Archimedes method, and bubble point method. The conditions for obtaining a pure phase were identified, and the transformation path of the phase during sintering and the mechanism of pore formation were provided. The linear sweep voltammetry (LSV) cure and cyclic voltammetry (CV) cure of MAX were tested using an electrochemical workstation. It can be calculated that MAX exhibits good hydrogen evolution reaction (HER) performance under alkaline conditions due to its high electrochemical active surface area (ECSA) of 373.2 and small Tafel slope of 41.7 ​mV·dec−1.

Highly wear resistant metal bond for diamond tool based on two-step reactive sintered Fe3Al

Metal bond diamond tools are regularly used in the machining of various hard and brittle materials. The mechanical properties and wear resistance of the metal bond are very important for the tool's life and machining performance. Herein, a low-cost and highly wear resistant Fe3Al bonded material for diamond tool was proposed. A novel two-step reactive sintering method, integrating short-term high-temperature reactive sintering and long-term low-temperature densification sintering, was proposed to prepare Fe3Al bond diamond tools. The effect of sintering temperature on the microstructure and mechanical properties of the Fe3Al bond was examined during one-step reactive sintering. The mechanical properties and tribological characteristics of the one-step and two-step reactive sintered Fe3Al and commercial Fe alloy bond were compared. The machining performance of the two-step reactive sintered Fe3Al bond diamond tool on sapphire was also examined and compared to that of a commercial Fe alloy bond diamond tool. The results showed that the relative density and mechanical properties of the Fe3Al bonded material were enhanced by increasing the sintering temperature during one-step reactive sintering. Moreover, the sample sintered at 1150-850 °C exhibited better mechanical properties and wear resistance compared to the one-step reactive sintered Fe3Al and commercial bond. The grinding ratio of the two-step reactive sintered Fe3Al bond diamond tool was 157 % higher than that of the commercial Fe alloy bond diamond tool.

Reactive Synthesis for Porous (Mo2/3Y1/3)2AlC Ceramics through Mo, Y, Al and Graphite Powders.

Through an activation reaction sintering method, porous (Mo2/3Y1/3)2AlC ceramics were prepared by Mo, Y, Al, and graphite powders as raw materials. The phase composition, microstructure, element distribution, and pore structure characteristics were comprehensively studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), Archimedes method, and bubble point method. A detailed investigation was conducted on the influence of sintering temperature on the phase composition. Possible routes of phase transition and pore formation mechanisms during the sintering process were provided. The experimental results reveal that at 650-850 °C, transition metals react with aluminum, forming aluminum-containing intermetallics and a small amount of carbides. At 850-1250 °C, transition metals collaborate with graphite, producing transition metal carbides. Then, at 1250-1450 °C, these aluminum intermetallics interact with transition metal carbides and remaining unreacted Y, Al, and C, yielding the final product (Mo2/3Y1/3) 2AlC. Simultaneously, the pore structure alters correspondingly with the solid-phase reaction at different reaction temperatures.

Performance improvement of polyethersulfone membranes with Ti3AlCN MAX phase in the treatment of organic and inorganic pollutants

In this work, the hydrophobic polyethersulfone (PES) membrane was modified by incorporating Ti3AlCN MAX phase. Synthesis of Ti3AlCN MAX phase was performed using the reactive sintering method. The scanning electron microscopy (SEM) images showed a 3D compressed layered morphology for the synthesized MAX phase. The Ti3AlCN MAX phase was added to the casting solution, and the mixed-matrix membranes were fabricated by the non-solvent induced phase inversion method. The performance and antifouling features of bare and modified membranes were explored by pure water flux, flux recovery ratio (FRR), and fouling resistance parameters. Through the modification of membranes by introducing the Ti3AlCN MAX phase, the enhancement of these features was observed, in which the membrane containing 1 wt% of MAX phase showed 17.7 L/m2.h.bar of permeability and 98.6% for FRR. Also, the separation efficiency of all membranes was evaluated by rejecting organic and inorganic pollutants. The Ti3AlCN MAX membranes could reject 96%, 95%, and 88% of reactive blue 50, Rose Bengal, and azithromycin antibiotics, respectively, as well as 98%, 80%, 86%, and 36% of Pb2+, As5+, Na2SO4, and NaCl, respectively. Finally, the outcomes indicated the Ti3AlCN MAX phase was an excellent and efficient novel additive for modifying the PES membrane.

Multifunctional Nanocomposites in B4C-Tic-Tib2-Sic-BN-Al2O3-Sialon-C Carbon Fiber System for Armor Fillets, Turbine Discs and Wings, High-Temperature Wear Resistant Nodes

Goal - to receive on first stage β - SIALON containing nanocomposites by reactive sintering method at 14000C, with nitrogen pro-cess from origin composition in TiC-BN-SiC-B4C-Si-Al-Al2O3 (nanopowder) system. By using this method of synthesis, it became possible to receive nanocomposites with different percentages of β - SIALON. Our task was to study the phase composition of re-ceived consolidated materials in the TiC-TiB2-BN-SiC-B4C-β-SiAlON-Al2O3 (nanopowder-400nm.) system. Method. The obtained mass was grounded in an attritor and the consolidated composite was obtained by hot pressing at 16200C during 40 minutes, with glass perlite (Armenia) dope 2 mass%, delaying at final temperature for 8 min, under 30 MPa pressure and vacuum – 10-3 Pa. Perlite from Aragatc contained 96 mas. % glass. To study the phase composition of the composites, we conducted an X-ray structural analysis on the DRON-3 device. And to study the microstructure, we conducted research on an optical microscope -AC100 and a raster electron microscope “Nanolab 7” of the company "OPTON”. The values of the electrical parameters of the studied composites were calculated on the basis of the ob-tained "lgp- t" dependence. We have studied mechanical properties. Result. In TiC-TiB2-BN-SiC-B4C- β-SiAlON-Al2O3 – C Carbon Fiber system we obtained nanocomposites with high mechanical proper-ties. The advantage of this method is that compounds, which are newly formed thanks to interaction going on at thermal treat-ment: Si3N4, Si, AlN are active, which contributes to β-SiALON formation at relatively low temperature, at 1300-13500C. It is evi-dent that inculcation of ALN in crystal skeleton of ß-Si3N4 is easier since at this temperature interval crystal skeleton of Si3N4 is still in the process of formation. ß-SiAlON was formed at 14500C. Part of boron carbide was transformed into boron nitride in ni-trogen environment and in titanium diboride, which in the case of both composites is in small quantities. Conclusion. The phase composition of the obtained composite provides high physical-technical and performance properties of these nanocomposites. Compression strength-2198 MPa, Bending strength-271 MPa, Thermal expansion coefficient a20-700-3.8 10-6 0C.

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.

Enhancement of piezoelectric properties of CaBi2Nb2O9 ceramics by Ce doping and direct reaction sintering

CaBi2Nb2O9 (CBN) with the Aurivillius phase has a high Curie temperature (TC) and remarkable fatigue resistance, which has great potential for application as high-temperature sensors. However, due to its low piezoelectric properties, its practical application remains a great challenge. In this paper, Ca1-xCexBi2Nb2O9 ceramics were prepared by the direct reaction sintering (DRS) and conventional preparation (CP) methods, respectively. The experimental results indicate that Ce doping can increase the piezoelectric coefficient d33 of CBN ceramics by about two times. Among them, the grain size of the samples prepared by the DRS method is finer and more uniform, and the d33 value of DRS samples is about 3.6–9.4 % higher than that of CP samples. The DRS sample Ca0·97Ce0·03Bi2Nb2O9 has a d33 value of 18.9 pC/N, a TC of 948 °C, and a resistivity of 1.1 × 105 Ω cm at 600 °C. This study shows that DRS method is an effective densification method, which can prepare CBN-based ceramics with excellent comprehensive properties, and provides an innovative preparation route to explore CBN-based ceramics with excellent piezoelectric properties.

The production system and structural characterization of CAMNi-xTIxO3 with x values ranging from 0.0 to 1.0 are investigated

In this work, we report the production of new composite perovskite manganite system CaMn ,Ti,O, with doping x = 0.25, 0.5 and 0.75, reaction sintering method solid state. Structural characterization was performed using the technique of X-ray Diffraction (XRD) and the Rietveld method, obtaining a tetragonal structure, with Prima spatial group (# 62) (a=5.3586a y a=5.2997A: b=7.5041 A y b=7.5526a; c+5.3l82& y c=5.3278A). In this paper takes the discussion on possible structural changes with changes in the system titanium CaMn, ,Ti,O,.

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.

Structural and microwave dielectric properties of LiZnSbO4 ceramcis for dielectric resonator antenna applications

New microwave dielectric ceramics of LiZnSbO4 were prepared by the reactive sintering method. Within the sintering temperature zone of 1350∘C–1385∘C, a single-phase LiZnSbO4 with an orthorhombic structure was identified by XRD refinement, which contains 10 molecular formula per unit cell (i.e., [Formula: see text]). The relative density and average grain size had a main effect on [Formula: see text] and [Formula: see text] value of the LiZnSbO4 ceramics, whereas the phase assemblage was responsible for its [Formula: see text]. The 1375∘C-sintered LiZnSbO4 specimens owned comparable low [Formula: see text], but ultra-high [Formula: see text][Formula: see text]GHz (nearly three times) compared to LiZnPO4 and LiZnVO4 ultra-high [Formula: see text][Formula: see text]GHz (nearly three times) compared to LiZnPO4 and LiZnVO4 manufactured, which showed a return loss as low as 37.4[Formula: see text]dB, maximum gain of 5.7[Formula: see text]dB and a fractional bandwidth of 3.9% (11.95–12.43[Formula: see text]GHz).

High-Entropy Diborides-Silicon Carbide Composites by Reactive and Non-Reactive Spark Plasma Sintering: A Comparative Study.

The reactive spark plasma sintering (R-SPS) method was compared in this work with the two-step SHS-SPS route, based on the combination of the self-propagating high-temperature synthesis (SHS) with the SPS process, for the fabrication of dense (Hf0.2Mo0.2Ti0.2Ta0.2Nb0.2)B2-SiC and (Hf0.2Mo0.2Ti0.2Ta0.2Zr0.2)B2-SiC ceramics. A multiphase and inhomogeneous product, containing various borides, was obtained at 2000 °C/20 min by R-SPS from transition metals, B4C, and Si. In contrast, if the same precursors were first reacted by SHS and then processed by SPS under the optimized condition of 1800 °C/20 min, the desired ceramics were successfully attained. The resulting sintered samples possessed relative densities above 97% and displayed uniform microstructures with residual oxide content <2.4 wt.%. The presence of SiC made the sintering temperature milder, i.e., 150 °C below that needed by the corresponding additive-free system. The fracture toughness was also markedly improved, particularly when considering the Nb-containing system processed at 1800 °C/20 min, whereas the fracture toughness progressively decreased (from 7.35 to 5.36 MPa m1/2) as the SPS conditions became more severe. SiC addition was found to inhibit the volatilization of metal oxides like MoO3 formed during oxidation experiments, thus avoiding mass loss in the ceramics. The benefits above also likely took advantage of the fact that the two composite constituents were synthesized in parallel, according to the SHS-SPS approach, rather than being produced separately and combined subsequently, so that strong interfaces between them were formed.

In-situ fabrication and characterization of W-ZrC composites via pressureless reaction sintering

This research presents a study on the fabrication and characterization of tungsten‑zirconium carbide (W-ZrC), an ultra-high temperature ceramic, using an in-situ reaction sintering method. Tungsten carbide (WC) and zirconia (ZrO2) powders were used as precursors to synthesize composites with three different ratios. The thermodynamic phase stabilities of the precursor materials were analyzed, and the reaction products were determined based on the total pressure within the system. The fabricated composites were characterized by their microstructures, porosities, hardnesses, and thermal conductivities. The results show that the composites exhibited distinct crystal phases, including those of tungsten, tungsten carbide (W2C), zirconium carbide (ZrC), and tetragonal zirconia (t-ZrO2). The reaction pathways were determined based on the composition ratios and thermodynamic stability. The composites demonstrate good densification and interparticle bonding owing to the in-situ reaction sintering process, which simplifies the fabrication and lowers processing costs. The composites also exhibited desirable properties, such as high hardness and thermal conductivity (maximum 36.4 W·m−1·K−1), making them suitable for high-temperature applications. The findings of this study contribute to the understanding of the synthesis process and properties of W-ZrC composites and provide insights for their potential applications to industries such as aerospace, defense, and nuclear energy.

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.

Influence of sintering atmosphere on the formation of ZrSiO4 by solid‐state sintering method

AbstractExploring the influence of sintering atmosphere on the formation of ZrSiO4 is of great significance. Herein, ZrSiO4 ceramics were prepared by the solid‐state reactive sintering method under different atmospheres (air, N2, vacuum, and Ar + 5%H2). The influence of sintering atmosphere on the phase and microstructure evolutions of the obtained ceramics was investigated. It was found that ZrSiO4 ceramics could be prepared under air atmosphere, whereas ZrO2–SiO2 glass ceramics were obtained under N2, vacuum, and Ar + 5%H2 atmosphere, which may be due to the fact that the oxygen‐deficient environment inhibits the transformation of ZrO2 to tetragonal phase (t‐ZrO2) and the crystallization of amorphous SiO2. The results demonstrated that t‐ZrO2 and c‐SiO2 were beneficial for the formation of ZrSiO4. The ZrSiO4 conversion fraction was up to 96.16% under air atmosphere at 1450°C for 6 h. Furthermore, the predominant formation mechanism of ZrSiO4 was the reaction between t‐ZrO2 and c‐SiO2.