A novel promotion strategy for microstructure and electrical performance of garnet electrolytes via Li4GeO4 additive

Cubic Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (c-LLZTO) electrolyte is one of the most promising solid electrolytes. However, it is rather difficult to promote its electrical performance while reducing process parameters. Therefore, Li₄GeO₄ is applied as the additive in liquid sintering of LLZTO ceramics in this study. The LLZTO@Li₄GeO₄/Li₂O composite electrolyte sintered at 1180 °C for 3 h performs a significantly promoted microstructure and electrical performance, the ionic conductivity of which reaches 5.77 × 10⁻⁴ S cm⁻¹ at 25 °C. The Li₄GeO₄/Li₂O eutectic phase contributed prominently, in which the high concentration of Li⁺ seaming the LLZTO grains tightly. Meanwhile, Li⁺ conduction in the consecutive conductive pathways constructed by [GeO₄] groups among the grains was greatly stimulated. With the modification of the grain boundary, an improved garnet electrolytes/Li anode interface performance is produced. The Li/Au|LLZTO@Li₄GeO₄/Li₂O|Au/Li symmetrical cell is able to cycle stably for more than 500 h at the current density of 0.1 mA cm⁻² at room temperature.     

Synthesis, spark plasma sintering and electrical conduction mechanism in BaTiO3-Cu composites

BaTiO₃-Cu composite powders were prepared via an alkoxide-mediated synthesis approach. As-synthesized BaTiO₃ nanoparticles were as small as 40 nm and coated partially larger Cu particles of approximately 1 μm in size. Thermogravimetric analysis (TGA) and dilatometry revealed a gradual increase in weight loss and retarded shrinkage with the increase of Cu addition. BaTiO₃-Cu composites were successfully densified by spark plasma sintering (SPS). The microstructures show an average grain-size for BaTiO₃ of around 100 nm and a crystallite size of about 1 μm for the Cu inclusions. The AC conductivity of the BaTiO₃-Cu composites increased with increasing Cu content or with temperature. The dominant electrical conduction mechanism in SPSed BaTiO₃-Cu composites changed from migration of oxygen vacancies to band conduction of trapped electrons in oxygen vacancies with the increase of Cu content.     

Solid-phase reaction mechanism and microwave dielectric properties of Mg2GeO4-MgAl2O4 composite ceramics

In this paper, a solution for simplifying the manufacture of Mg₂GeO₄-MgAl₂O₄ ceramics is reported. The Mg₂GeO₄-MgAl₂O₄ ceramics were obtained from MgO, Al₂O₃ and GeO₂ powders using the solid phase reaction approach. The phase structure, microscopic morphology and elemental composition of the Mg₂GeO₄-MgAl₂O₄ ceramics were specifically analyzed with XRD, SEM and EDS. The samples contain Mg₂GeO₄ and MgAl₂O₄ phases and no other phases are formed. The ceramics have a homogeneous and dense microstructure. This simplified preparation method saves preparation costs and improves the firing behavior of the ceramics, enhancing the microwave dielectric properties of Mg₂GeO₄-MgAl₂O₄ ceramics. Excellent microwave dielectric properties with ε_r = 8.0, Q × f = 150000 GHz and τ_f = ?34 ppm/°C were attained for Mg₂GeO₄-MgAl₂O₄ ceramics sintered at 1600 °C.     

Effect of BaOB2O3 composite sintering aid on sinterability and electrical property of BaZr0.85Y0.15O3-δ ceramic

Yttrium-doped barium zirconate (BZY) has been extensively studied as a promising electrolyte material for protonic ceramic fuel cells. However, inferior sinterability is a major barrier in BZY development. In our research, the effect of BaOB₂O₃ composite sintering aid on the sintering behavior and electrical property of BaZr_0.85Y_0.15O_3-δ (BZY15) are examined. BaOB₂O₃ addition reduces the sintering temperature of BZY15 by approximately 200 °C via the liquid-phase sintering mechanism. The corresponding bulk and grain boundary conductivities are prominently improved (<3 wt% BaOB₂O₃ addition), whereas the further addition of sintering aid decreases the grain boundary conductivity. Notably, the scanning electron microscope (SEM) and electrochemical impedance spectroscopy (EIS) analyses suggest that the enhanced conductivity may be related to the temperature dependence of Ba evaporation.     

Effects of Bi2O3 and Li2OB2O3Bi2O3SiO2 glass on electromagnetic properties of NiCuZn/BaTiO3 composite material at low sintering temperature

Bi₂O₃ and Li₂OB₂O₃Bi₂O₃SiO₂ (LBBS) glass were introduced into Ni_0.15Cu_0.24Zn_0.61Fe₂O₄BaTiO₃ ((NCZF-BTO) composite materials as sintering aids and sintered at 920?°C. Effects of Bi₂O₃ and LBBS glass on phases, microstructures, magnetic and dielectric properties of these composites were comparatively studied. In contrast to undoped composites, the addition of Bi₂O₃ or LBBS glass to samples enhances performance. Hence, when Bi₂O₃ content reached 1.5?wt%, saturation magnetization (4πM_s) increased from 3825.4 to 4912.5 Gs, static permeability (μ₀) increased from 53.2 to 197, and dielectric constant (ε′) increased from 18.3 to 23.4. When LBBS glass content reached 1.5?wt%, 4πM_s increased to 4145.6 Gs, μ₀ increased to 79.3, ε′ increased to 25.4. However, both coercivity (H_c) and dielectric loss (tan?δ) were reduced. In short, Bi₂O₃ promoted magnetic properties, whereas LBBS glass promotes dielectric properties more effectively.     

The effect of yttrium nitrate addition on the densification behaviour of Y2O3 ceramics during the cold sintering process

The densification behaviour and phase development of Y₂O₃ ceramics were investigated as a function of yttrium nitrate (Y(NO₃)₃·6H₂O) solution addition during the cold sintering process at 200 °C. Second phases such as Y₄O(OH)₉NO₃ and Y(OH)₃ were observed after the cold sintering process. The amount of Y₄O(OH)₉NO₃ increased with increasing amount of yttrium nitrate, while the amount of Y(OH)₃ decreased. The second phases were transformed to fine sized Y₂O₃ (∼30 nm) particles smaller than those of the raw powder (<400 μm) by sintering at 600 °C. The fine sized Y₂O₃ particles were located in the voids between the larger Y₂O₃ particles, thus increasing the packing density and enhancing the densification of the Y₂O₃ ceramics after the final sintering process.     

Effect of Li2O content and sintering temperature on the grain growth and electrical properties of Gd-doped CeO2 ceramics

The sintering behavior and electrical properties of Gd-doped CeO₂ (GDC), with and without Li₂O as a sintering additive, were examined. With increasing Li₂O content, the grain growth of GDC was enhanced because of an increase in the duration for which a Li-rich liquid phase existed during sintering. The migration of Li ions led to an increase in the electrical conductivity of the Li-doped GDC. When the Li-doped GDC was sintered at a high temperature of 1400 °C, the Li evaporated, resulting in a decrease in the electrical conductivity.     

Influence of Li doping on the morphological evolution and optical & electrical properties of SnO2 nanomaterials and SnO2/Li2SnO3 composite nanomaterials

SnO₂ nanomaterials and SnO₂/Li₂SnO₃ composite nanomaterials doped with different Li contents were synthesized via a simple one-step thermal evaporation method. X-ray diffraction patterns showed that with the increase of Li doping, the intensity of Li₂SnO₃ diffraction peaks gradually increased, while that of SnO₂ diffraction peaks gradually decreased. With the increase of Li doping, the width of nanobelts gradually increased, with the morphology changing from banded structure to standard hexagonal sheet structure. The Raman scattering spectra indicated that with the increase of Li doping, the peak of Li₂SnO₃ at 588.8 cm^?1 kept increasing, and the strongest vibration mode A_1g in SnO₂ gradually weakened. X-ray photoelectron spectroscopy revealed that with the increase of Li doping, the surface electrophilic oxygen species in SnO₂/Li₂SnO₃ composite nanomaterials greatly increased. Under the condition of light irradiation with a wavelength of 505 nm, the bright current of the Li-doped SnO₂ samples was higher than the dark current, while that of the SnO₂/Li₂SnO₃ composite nanomaterials was higher than the dark current, which was mainly due to more oxygen vacancies in SnO₂/Li₂SnO₃ composite nanomaterials than electrons excited by light. Consequently, positive photoconductivity gradually weakened, and even the negative photoconductivity emerged.     

Preparation and performance of Na-doped La2Ce2O7 electrolytes for protonic ceramic fuel cells

The protonic material La₂Ce₂O₇ exhibits good tolerance to H₂O and CO₂ compared to BaCeO₃-based materials and has become increasingly popular for operation at low-to-intermediate temperatures in protonic ceramic fuel cells. In this work, doping La₂Ce₂O₇ with Na in a series with varying compositions is studied. All of the precursors are prepared by a common citrate-nitrate combustion method. X-ray diffraction images reveal that all of the La_2-xNa_xCe₂O_7-δ samples have a cubic structure. The La_2-xNa_xCe₂O_7-δ pellets are characterized by scanning electron microscopy and are observed to be dense without holes. The effects of Na-doping on the La₂Ce₂O₇ electrical conductivity are carefully investigated in air at 350–800 °C and 5%H₂-95% Ar environments at 350–700 °C. It is found that different levels of Na doping in La₂Ce₂O₇ are conducive to improving the electrical conductivity and sinterability. Among the pellets, La_1.85Na_0.15Ce₂O_7-δ exhibited the highest electrical conductivity in air and 5% H₂-95% Ar atmospheres. Anode-supported half cells with La_1.85Na_0.15Ce₂O_7-δ electrolyte are also fabricated via a dry-pressing process, and the corresponding single cell exhibited a desirable power performance of 501 mW cm⁻² at 700 °C. The results demonstrate that La_1.85Na_0.15Ce₂O_7-δ is a promising proton electrolyte with high conductivity and sufficient sinterability for use in protonic ceramic fuel cells operating at reduced temperatures.     

Synthesis and electrochemical performance of Li4Ti5O12/Ag composite prepared by electroless plating

To improve the electrochemical and anti flatulence performance of Li₄Ti₅O₁₂, Ag modified Li₄Ti₅O₁₂ (LTO) with high electrochemical performance as anode materials for lithium-ion battery was synthesized successfully by two-step solid phase sintering and subsequent electroless plating process in the presence of silver. The effect of Ag modification on the physical and electrochemical properties were investigated by the extensive material characterization of X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM). The results showed that the samples possessed single spinel structure, it could be observed that the LTO/Ag composite and the pure LTO shared the same vibration frequencies, which indicated that the crystal structure of LTO didn’t change after electroless plating process, and the particles were uniformly and regularly shaped within 0.5–1.0 µm. Electrochemical performance of the samples were evaluated by the charging and discharging, cyclic voltammetry, electrochemical impedance spectroscopy, cycling and rate tests. It's obvious that the LTO/Ag composite prepared at the 10 min of electroless plating showed the highest performance with capacitance of 182.3 mA h/g at 0.2 C current rates. What's more, the LTO/Ag composites still maintained 92% of its initial capacity even after 50 charge/discharge cycles. Modification of appropriate Ag not only benefits the reversible intercalation and deintercalation of Li⁺, but also improves the diffusion coefficient of lithium ion. Besides, modification of appropriate Ag lower electrochemical polarization leads to higher conductivity and cycle performance of LTO, which is consistent with the results of the best reversible capacities.     

Microwave dielectric properties,low-temperature sintering mechanism,and defects behaviour of temperature stable (1-x)Li2Zn3Ti4O12-xSr3(VO4)2 ceramics

(1-x)Li₂Zn₃Ti₄O₁₂-xSr₃(VO₄)₂ (0.1 ≤ x ≤ 0.4) microwave dielectric ceramics were fabricated by solid-state sintering technology. The impact of SV addition on the microstructure, dielectric properties, sintering process, and defects behaviour was studied. The formation of SrTiO₃ and the glass phase were observed via XRD and TEM, and the latter resulted in a decrease in the sintering temperature. The variations in microwave dielectric properties were consistent with the empirical mixture rules calculated by XRD refinement, and a near-zero τ_f value was obtained. The Li, Zn and V elements of the glass phase and the liquid phase sintering model were deduced via DSC, TEM and Raman spectroscopy. Then, the defect behaviour, such as oxygen vacancies, Ti³⁺, and V⁴⁺, was investigated by XPS and complex impedance spectroscopy. It was found that the generation and migration of defects occurred much more easily in 0.7LZT-0.3 SV than in LZT, resulting in a higher dielectric loss. Finally, the 0.7Li₂Zn₃Ti₄O₁₂-0.3Sr₃(VO₄)₂ ceramic sintered at 900 °C exhibited excellent microwave dielectric properties of ε_r = 17.8, Q × f = 41,891 GHz, and τ_f = ?4.4 ppm/°C and good compatibility with silver electrode, showing a good potential application for LTCC.     

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.     

多孔Al2O3/SiC、MoSi2/SiC复合材料的制备及吸波性能

以Si、Al₂O₃、MoSi₂微粉和生物竹材为原料,采用包埋烧结法分别制备出SiC多孔材料、Al₂O₃/SiC、MoSi₂/SiC复合材料。采用XRD、SEM及波导法测试其物相组成、显微结构及吸波性能。结果表明：MoSi₂/SiC复合材料的厚度为2 mm时有明显的吸波特性,有效吸收带宽在X波段的9.65~12.4 GHz频率范围内达2.75 GHz,且最低反射损耗为-38.27 dB。Al₂O₃/SiC复合材料孔道内的Al₂O₃与SiC晶须交缠,形成大量电偶极矩,产生介电损耗;MoSi₂/SiC复合材料除介电损耗外还存在电阻损耗,使得复合材料电磁损耗增加,是较有前途的结构功能吸波材料。     

Reactive melt infiltration fabrication of C/C-SiC composite: Wetting and infiltration

Reactive melt infiltration is a fast and economical fabrication process for high performance C/C-SiC composite. In order to help understanding reactive melt infiltration production of C/C-SiC composite by liquid silicon, wetting and infiltration of the porous C/C composite preform by liquid silicon were investigated using a sessile drop technique. The contact angle decreased with the increase of time while the drop base diameter increased. According to the variation of drop base diameter and contact angle as a function of time, four different stages corresponding to the interfacial reaction and infiltration of liquid silicon were identified during wetting of the porous C/C composite preform by the liquid silicon. The infiltration height based on wetting curve linearly increased with time, much smaller than that calculated according to Washburn equation, which strongly indicated the reaction control of silicon infiltration.     

Promoting the Li storage performances of Li2ZnTi3O8@Na2WO4 composite anode for Li-ion battery

In this work, a reasonable strategy for the construction of Li₂ZnTi₃O₈@Na₂WO₄ composite was employed to promote the Li storage performances of Li₂ZnTi₃O₈. The Li₂ZnTi₃O₈@Na₂WO₄ composites (5, 10, and 15 wt%) were then prepared by a solution dispersion method. The introduction of Na₂WO₄ does not change the structures of the samples and they show similar morphologies with particle sizes from 100 to 200 nm. Suitable amount of Na₂WO₄ modification effectively improves the electrochemical performance of Li₂ZnTi₃O₈. Li₂ZnTi₃O₈@Na₂WO₄ composites (0, 5, 10, and 15 wt%) deliver the discharge/charge capacities of 137.4/136.4, 164.2/162.3, 189.2/188.1, and 154.5/153.3 mAh g^?1 at 0.5 A g^?1 after 100 cycles, respectively. Li₂ZnTi₃O₈@Na₂WO₄ composites (10 wt%) has the highest reversible capacities among all samples. The Na₂WO₄ shell with an excellent electronic conductivity can reduce electrode polarization, decrease the charge transfer resistance, enhance the Li-ion diffusion coefficient of Li₂ZnTi₃O₈, and then improve the electrochemical kinetics of composites. In addition, the formation of Ti–O bonds at the interface can be helpful for the stabilization of the composite, being beneficial for the improvement of their cycling stabilities. These results reveal that Na₂WO₄ coating is a facile and effective strategy to promote the Li storage performance of Li₂ZnTi₃O₈.     

Preparation and characterization of GDC-Li2SO4/Li2CO3 nanocomposite electrolytes for applications in intermediate solid oxide fuel cells

Gd_0.1Ce_0.9O_1.95/Li₂CO₃-Li₂SO₄ (GDC/LCS) nanocomposite electrolytes were prepared through nano-powders mixing, prefiring and sintering operations. The phase components and microstructures of the as-prepared nanocomposite were characterized by XRD, FESEM, TG-DSC and IR spectroscopy. AC impedance spectroscopy and DC polarization method were utilized to measure their electrical conductivities under different conditions. It has been found that the GDC/LCS nanocomposite have a very homogeneous microstructure, where the LCS is mostly in amorphous state due to the strong interfacial interactions between the GDC and LCS. In addition, their overall electrical conductivity was found to increase with temperature in air, featured with a sharp activation energy change from 1.01 to 0.30 eV around 520 °C, and reach 108.7 mS/cm at 600 °C, while their protonic and oxide ionic conductivities were 16 mS/cm in H₂ and 5 mS/cm in air at the same temperature, respectively. The single cell built up of the GDC/LCS nanocomposite showed an open-circuit voltage of 1.01 V and peak power density of 272 mW/cm² at 600 °C.     

Preparation,microstructure and electrical property of GdSmZr2O7-(Li0.52Na0.48)2CO3 composite electrolyte via carbonate infiltration

Porous GdSmZr₂O₇ (GSZ) with different porosities has been prepared by the solid state reaction, and GSZ-carbonates composites have been prepared by infiltrating (Li_0·52Na_0.48)₂CO₃ (LNC) molten carbonates. Phase structure, microstructure and electrical property have been analyzed by X-ray diffractometer (XRD), scanning electron microscope (SEM) and electrochemical impedance spectroscopy (EIS). SEM results show that the voids in porous GSZ are uniformly distributed. The relative density of GSZ-LNC composites obtained by molten salt infiltration is above 93%. The electrical conductivity of the GSZ-LNC composites obtained by molten salt infiltration reaches the highest value of 0.50 S cm⁻¹ at 600 °C, which is much higher than that of GSZ-LNC composites prepared by traditional mechanical mixing method. This excellent electrical property strongly indicates that the GSZ-LNC composite obtained by molten salt infiltration is a promising ionic conductor.     

Li2O-Al2O3-SiO2系统玻璃的晶化和烧结

采用差热分析（DTA）,X射线衍射分析（XRD）和扫描电子显微镜（SEM）等分析手段研究了Li2O-Al2O3—SiO2 （LAS）系统玻璃的烧结和析晶.通过实验确定了最佳烧结温度,并获得主晶相为β—锂辉石的Li2O-Al2O3—SiO2 （LAS）的微晶玻璃.结合烧结体的体积密度、显气孔率和吸水率的数据,分析说明了粘结剂PVA的加入对玻璃粉烧结体性能的影响.     

Fabrication of Lu2Ti2O7-Lu3NbO7 solid solution transparent ceramics by spark plasma sintering and their electrical conductivities

The Lu₂Ti₂O₇-Lu₃NbO₇ system, belonging to A₂B₂O₇ with a cubic structure, is attractive for tailored properties by substitution. In this study, Lu_2+0.25xTi_2−0.5xNb_0.25xO₇ (x = 0–4) transparent ceramics were fabrication by reactive spark plasma sintering using commercially available Lu₂O₃, TiO₂ and Nb₂O₅ powders. The phase evolution, microstructure, density, transmittance and electrical conductivity were investigated as a function of composition parameter x. The results showed that Lu_2+0.25xTi_2−0.5xNb_0.25xO₇ transparent ceramic had a pyrochlore structure at x = 0 and 1, while preserved a defect-fluorite structure at x = 2–4. The lattice parameter and theoretical density increased linearly, while the average grain size decreased steadily with increasing composition parameter x. All the specimens exhibited a dense microstructure and the highest in-line transmittance was 64% at 550 nm for x = 4. The bulk conductivity increased with increasing x, reaching a maximum value of 4.2 × 10⁻² S m^-1 for Lu₃NbO₇ at 1073 K.     

Fabrication and mechanical properties of Al2O3-Si3N4/ZrO2-Al2O3 laminated composites

In this paper, Al₂O₃-Si₃N₄/ZrO₂-Al₂O₃ laminated composites were fabricated by tape casting and hot press sintering, and the relationships between the process, microstructure, and mechanical properties of Al₂O₃-Si₃N₄/ZrO₂-Al₂O₃ laminated composites were determined. The SiAlON phase was found in the Al₂O₃-Si₃N₄ layer, and liquid-phase sintering was proposed. Nano-scratch tests were carried out to investigate the interface bonding strength of the laminates. The distribution of residual stresses, generated due to the different coefficients of thermal expansion between the different layers, was estimated according to lamination theory and confirmed using Vickers indentation. When the sintering temperature was 1550 °C, the sintered laminated ceramics had good mechanical properties, with a maximum strength and toughness of 413 MPa and 6.2 MPa m^1/2, respectively. The main toughness mechanics of laminated composites was residual stress.