Preparation of dual-phase composite BaCe0.8Y0.2O3/Ce0.8Y0.2O2 and its application for hydrogen permeation

Dual-phase ceramic membranes composed of BaCe_0.8Y_0.2O₃ (BCY) and Ce_0.8Y_0.2O₂ (CYO) were successfully synthesized by solid state reaction method for hydrogen permeation. The influences of the BCY/CYO volume ratios on phase composition, microstructure, chemical stability and electrical property were investigated. The hydrogen permeation of the dual-phase composite was characterized as a function of temperature and feed side hydrogen partial pressure. The results showed that there was no reaction between the two constituent oxides observed under the preparation conditions. The dual-phase composite with different BCY/CYO volume ratios after sintering at 1550 °C exhibited dense structure, as well as good stability in 4% H₂/Ar, wet Ar and pure CO₂ atmosphere. The conductivity of the dual-phase composite increased with the content of CYO increasing and 30BCY–70CYO exhibited the highest total conductivity of 2.6×10⁻² S cm⁻¹ at 800 °C in 4% H₂/Ar. The hydrogen permeability of 30BCY–70CYO sample was improved as the temperature and the hydrogen partial pressure in feed gas increased. The hydrogen permeation flux of 1.7 μmol cm⁻² s⁻¹ was achieved at 850 °C.     

Promoting Influence of Doping Indium into BaCe0.5Zr0.3Y0.2O3‐δ as Solid Proton Conductor

The influence of indium doping on chemical stability, sinterability, and electrical properties of BaCe_0.5Zr_0.3Y_0.2O_3‐δ was investigated. The phase purity and the chemical stability of the powders in humid pure CO₂ were evaluated by XRD. The dense electrolyte pellets were formed after the calcination at 1450°C for 8 h. SEM images and shrinkage plot showed that the sinterability of the samples was apparently improved by doping indium. The electrical conductivity was measured by impedance test through two‐point method, at both low (200–350°C) and high temperature ranges (450–850°C) in different atmospheres. BaCe_0.4Zr_0.3In_0.1Y_0.2O_3‐δ has been proved to be the optimal composition which simultaneously maximized the chemical stability, sinterability, and electrical conductivity which reached 1.1 × 10^?2 S/cm in wet hydrogen at 700°C, comparing with the 1.3 × 10^?2 S/cm for original BaCe_0.5Zr_0.3Y_0.2O_3‐δ. Anode support fuel cell with a thin BaCe_0.4Zr_0.3In_0.1Y_0.2O_3‐δ electrolyte (15 μm) was fabricated by spin coating method. Maximum power density of 0.651 W/cm² was obtained when operating at 700°C and fed by humid H₂ (containing H₂O 3 vol%). The obtained fuel cell could efficiently run at 650°C for more than 100 h without any attenuation.     

Pechini法合成BaCe0.7Zr0.2Gd0.1O3-δ质子导体

采用Pechini法合成了用Zr部分取代Ce并用Gd掺杂的新型高温质子导体BaCe0.7Zr0.2Gd0.1O3-δ陶瓷前驱体，前驱体在1100℃煅烧得到了钙钛矿结构的陶瓷体。前躯体用TG—DTA分析了煅烧特性，用XRD测定了陶瓷粉体的相组成。陶瓷粉体压制成试样后在1450℃烧结后，经密度测试和SEM微观结构观察，证实得到了致密陶瓷体，其实测烧结密度大于理论密度的92％。     

Partial oxidation of methane to syngas in BaCe0.15Fe0.85O3−δ membrane reactors

Dense planar Ba_0.15Ce_0.85FeO_3−δ (BCF1585) membrane reactors were investigated to produce syngas from methane. Firstly, the membrane itself catalytic activity to methane was investigated using a blank BCF1585 without any catalysts. Then a LiLaNi/γ-Al₂O₃ catalyst was packed on the BCF1585 membrane surface to test the synergetic effects of the membrane and catalyst. It was found that the membrane itself has a poor catalytic activity to methane. The main products are CO₂ and C₂, and methane conversion is low due to the low oxygen permeation flux. However, after the catalyst was packed on the membrane surface, both methane conversion and oxygen permeation flux were greatly improved by the synergetic effect between the membrane and catalyst. Carbon monoxide selectivity reached at 96% with methane conversion of up to 96%. The oxygen permeation flux reached at 3.0 mL/cm² min at 850 °C for a 1.5 mm disk membrane and can effectively be increased by reducing the thickness of the membranes. After operation for 140 h at 850 °C, the used membrane was examined with SEM and EDXS. The results revealed that the decomposition of the membrane materials could not be avoided under such conditions. Oxygen partial pressure gradient across the membranes is suggested as a critical factor to accelerate the kinetic decomposition of the materials.     

Marked reduction in the thermal conductivity of (La0.2Gd0.2Y0.2Yb0.2Er0.2)2Zr2O7 high-entropy ceramics by substituting Zr4+ with Ti4+

The (La_0.2Gd_0.2Y_0.2Yb_0.2Er_0.2)₂(Zr_1-xTi_x)₂O₇ (x = 0–0.5) high-entropy ceramics were successfully prepared by a solid state reaction method and their structures and thermo-physical properties were investigated. It was found that the high-entropy ceramics demonstrate pure pyrochlore phase with the composition of x = 0.1–0.5, while (La_0.2Gd_0.2Y_0.2Yb_0.2Er_0.2)₂Zr₂O₇ shows the defective fluorite structure. The sintered high-entropy ceramics are dense and the grain boundaries are clean. The grain size of high-entropy ceramics increases with the Ti⁴⁺ content. The average thermal expansion coefficients of the (La_0.2Gd_0.2Y_0.2Yb_0.2Er_0.2)₂(Zr_1-xTi_x)₂O₇ high-entropy ceramics range from 10.65 × 10^?6 K^?1 to 10.84 × 10^?6 K^?1. Importantly, the substitution of Zr⁴⁺ with Ti⁴⁺ resulted in a remarkable decrease in thermal conductivity of (La_0.2Gd_0.2Y_0.2Yb_0.2Er_0.2)₂(Zr_1-xTi_x)₂O₇ high-entropy ceramics. It reduced from 1.66 W m^?1 K^?1 to 1.20 W m^?1 K^?1, which should be ascribed to the synergistic effects of mass disorder, size disorder, mixed configuration entropy value and rattlers.     

Influence of anode pore forming additives on the densification of supported BaCe0.7Ta0.1Y0.2O3−δ electrolyte membranes based on a solid state reaction

We describe a solid state reaction for the preparation of both NiO–BaCe_0.7Ta_0.1Y_0.2O_3?δ anode substrates and BaCe_0.7Ta_0.1Y_0.2O_3?δ (BCTY10) electrolyte membranes on porous NiO–BCTY10 anode substrates. The amounts of the pore forming additive in the substrates showed a significant influence on the densification of the BCTY10 membranes. After sintering at 1450 °C for 5 h, the BCTY10 membrane on a NiO–BCTY10 anode containing 30 wt.% starch achieved a high density and showed adequate chemical stability against H₂O and CO₂. The chemical stability of BCTY10 was even better than that of BaCe_0.7Zr_0.1Y_0.2O_3?δ. With a mixture of BaCe_0.7Zr_0.1Y_0.2O_3?δ (BZCY7) and La_0.7Sr_0.3FeO_3?δ (LSF) as a cathode, a single fuel cell with 12 μm thick BCTY10 electrolyte generated maximum power densities of 142, 93, 29 mW/cm² at 700, 600 and 500 °C, respectively. The electrolyte resistance and interfacial polarization resistance of the cell under open circuit conditions were also investigated.     

Thermal properties of (Zr0.2Ce0.2Hf0.2Y0.2RE0.2)O1.8 (RE= La,Nd and Sm) high entropy ceramics for thermal barrier materials

The high-entropy ceramic materials (Zr_0.25Ce_0.25Hf_0.25Y_0.25)O_1.875 (H-0) and (Zr_0.2Ce_0.2Hf_0.2Y_0.2RE_0.2)O_1.8 (H-RE) (RE = La, Nd and Sm) with fluorite structure and homogeneous element distribution were prepared. With fluorite structure, fine grain size and high density, the H-0 and H-RE ceramics displayed low thermal conductivity, suitable thermal expansion coefficient, high hardness and fracture toughness. The effect of La, Nd and Sm on the mechanical, heat conductivity and heat expansion properties of high entropy ceramics were discussed. The single-phase high-entropy ceramic materials in this work are very suitable for application as thermal barrier materials.     

Low-temperature joining of SiC ceramics with Y2O3-Al2O3 interlayer by SiO2-based liquid phase extrusion strategy

In order to reduce the joining temperature of SiC ceramics by glass-ceramic joining, some oxides were usually introduced into to Y₂O₃–Al₂O₃ for reducing the eutectic temperature. However, the joints might have poor high-temperature resistance due to the low melting point of the joining layer. In the present work, based on novel SiO₂-based liquid phase extrusion strategy, joining of SiC ceramics with Y₂O₃–Al₂O₃ interlayer was carried out by using Y₂O₃–Al₂O₃–SiO₂ as the filler through spark plasma sintering (SPS). The SiO₂-free interlayer of Y₂O₃–Al₂O₃ was used for comparison. It was found that SiC joints using Y₂O₃–Al₂O₃ could be only joined at a high temperature of 1800 °C, and the thickness of the interlayer was about 20 μm. The shear strength of the joint obtained at 1800 °C was 89.62 ± 4.67 MPa and the failure located in the SiC matrix. By contrast, reliable joining of SiC ceramics could be finished at as low as 1550 °C by extrusion of SiO₂-containing liquid phase when using Y₂O₃–Al₂O₃–SiO₂ as the interlayer, alongside the interlayer thickness of only several microns. The joint strengths after joining at 1550 °C was 84.90 ± 3.48 MPa and the failure located in matrix position. The joining mechanism was discussed by combining the detailed microstructure analysis and phase diagram.     

Orthorhombic to tetragonal polymorphic transformation of YTa3O9 and its inhibition through the design of high-entropy (Y0.2La0.2Ce0.2Nd0.2Gd0.2)Ta3O9

To explore the mechanism of phase transformation, YTa₃O₉ was prepared by an integrated one-step synthesis and sintering method at 1500 °C using Y₂O₃ and Ta₂O₅ powders as starting materials. High-temperature XRD patterns and Raman spectra showed that a phase transformation from orthorhombic to tetragonal took place in YTa₃O₉ through the bond length and angle changes at 300–400 °C, which caused a thermal conductivity rise. To inhibit the phase transformation, a high-entropy (Y_0.2La_0.2Ce_0.2Nd_0.2Gd_0.2)Ta₃O₉ (HE RETa₃O₉) was designed and synthesized at 1550 °C using the integrated solid-state synthesis and sintering method. In tetragonal structured HE RETa₃O₉, phase transformation was inhibited by the high-entropy effect. Furthermore, HE RETa₃O₉ exhibited low thermal conductivity, and its tendency to increase with temperature was alleviated (1.69 W/m·K, 1073 K). Good phase stability, low thermal conductivity and comparable fracture toughness to YSZ make HE RETa₃O₉ promising as a new thermal barrier coating material.     

On the formation mechanism of Ba0.85Ca0.15Zr0.1Ti0.9O3 thin films by aqueous chemical solution deposition

Here we report on the development of an environmentally friendly, simple and robust aqueous chemical solution route for the fabrication of Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃ (BCZT) thin films. Using a stable aqueous precursor solution, thin films were prepared by spin coating and the impact of thermal processing on the microstructure and phase purity of the thin film was revealed by X-ray diffraction and transmission electron microscopy. We find, that barium oxycarbonate formation during the pyrolysis plays a key role in the formation of dense, homogeneous single phase BCZT films. The formation of barium oxycarbonate leads to undesirable segregation of cations, resulting in barium depletion on the BCZT grain boundaries and occurrence of a secondary phase (CaZrTi₂O₇). Based on this insight the thermal processing was optimized and dense, oriented and single-phase BCZT films were fabricated by combining a low pyrolysis temperature with rapid heating to the annealing temperature.     

Enhanced energy storage property in glass-added Ba(Zr0.2Ti0.8)O3-0.15(Ba0.7Ca0.3)TiO3 ceramics and the charge relaxation

Glass additive BaO-SrO-TiO₂-Al₂O₃-SiO₂-BaF₂ is employed to enhance the microstructures and energy storage properties of the Ba(Zr_0.2Ti_0.8)O₃-0.15(Ba_0.7Ca_0.3)TiO₃ ceramics. To clarify the energy storage mechanism, the charge transportation and polarization process are investigated by thermally simulated depolarization current (TSDC). The dielectric breakdown strength increases from 4.3?kV/mm to 10.8?kV/mm for BZT-0.15BCT ceramics with 11?wt% glass additives, indicating that glasses could refine the grain size, uniform the structure, and decrease defects. Due to the micro-domain region, dielectric relaxation behavior is observed with a broadened and reduced dielectric constant peak at a large dielectric constant of about 3000?at room temperature. The largest charge energy density of 1.45?J/cm³ and discharge density of 0.17?J/cm³ are achieved for BZT-0.15BCT glass ceramics with 7?wt% glass additives. TSDC results demonstrate that dipole origin movement and charge transportation have an important effect on the dielectric properties and dielectric breakdown strength, respectively, which are largely influenced by the defects distribution state at the interfaces. Moderate domain walls could restrain the defects to inhibit the charge transportation and are harmful for the dielectric properties inversely. To achieve excellent energy storage performance, moderate domain walls are compromise of slightly degrading dielectric properties and greatly improving dielectric breakdown strength.     

Effect of Ba Nonstoichiometry in Bax(Zr0.8Y0.2)O3−δ on Population of 5‐Coordinated Y

The local environments of Y in the Y‐substituted BaZrO₃ of the starting compositions of Ba_x(Zr_0.8Y_0.2)O_3?δ (x = 0.97, 1.0, 1.03, and 1.06) were analyzed by ⁸⁹Y magic angle spinning NMR spectroscopy. The result showed a strong population dependence of 5‐coordinated Y³⁺ ions mostly at the B site on the Ba contents. The enhancement of Ba contents by 9 at% (from 0.97 to 1.06 in the starting Ba contents) in a nominal composition increased the amount of 5‐coordinated Y³⁺ ions from 35% ± 7% to 49% ± 5%, suggesting the importance of maximizing the Ba contents to populate more oxygen vacancies which is related to the concentration of protons incorporated during the hydration process. The wide variation in the lattice parameter of yttrium‐substituted BaZrO₃ perovskite materials in previous reports was reinterpreted with the variation in the Ba contents resulting from the evaporation of BaO during the sintering processes. Y³⁺ ions were confirmed to replace mainly the Zr⁴⁺ ions, as expected, and a tendency of oxygen vacancy clustering near the Y³⁺ ions was discussed.     

Effect of Li2O excess in Li6.4Ga0.2La3Zr2O12 electrolyte for all-solid-state Li-ion batteries

Li₇La₃Zr₂O₁₂ is a promising material used as solid electrolyte in all-solid-state lithium batteries. However, the lithium ionic conductivity of LLZO is limited, and the cycling stability of lithium symmetric battery based on LLZO is not good. In this research, different Ga-doped LLZO samples were prepared by adding different excess amounts of Li₂O, and the effect of excess amount of Li₂O on the structure and performance of LLZO have been researched. The results show that with the rise of the amount of Li₂O, the lithium ionic concentration increases gradually, and the lithium ionic conductivity and the ratio of grain resistance to total resistance rise first and then drop. When the excess amount of Li₂O is 10 wt.%, the sample exhibits the highest lithium ionic conductivity of 1.36 mS/cm, and the lithium symmetric battery exhibits the most stable operation.     

Enhanced voltage endurance capability of Ba(Zr0.2Ti0.8)O3 thin films induced by atomic-layer-deposited Al2O3 intercalations and the application in electrostatic energy storage

Ultrathin Al₂O₃ insulating intercalations with different thicknesses and numbers, prepared by atomic layer deposition technology, were introduced into Ba(Zr_0.2Ti_0.8)O₃ (BZT) relaxor ferroelectric films as the dielectric for electrostatic energy storage capacitors. The phase structure, microstructure and electrical properties were investigated in detail. Due to the insertion of insulating layers, the films show less leakage current and enhanced voltage endurance capability when the thickness of single Al₂O₃ intercalation exceeds a threshold (0.45–0.9 nm). The voltage endurance capability can be more enhanced by increasing the number of Al₂O₃ intercalations. For energy storage applications, the energy storage density and efficiency obtained from the polarization-electric field loops are significantly improved owing to the suppressed leakage and enhanced voltage endurance ability. The results promote the application of BZT-based films in electrostatic energy storage. It is demonstrated that the introduction of atomic-layer-deposited insulating intercalations with controllable thickness, such as those fabricated by ALD method, is an effective way to improve the electrical performance of devices based on composite materials.     

Phenomenological modeling of phase transitions and electrocaloric effect in Ba(Zr0.2Ti0.8)O3-(Ba0.7Ca0.3)TiO3

Ba(Zr_0.2Ti_0.8)O₃-x(Ba_0.7Ca_0.3)TiO₃ (BZT-xBCT) is a promising lead-free ferroelectric system. In this paper, we present two sets of free energy coefficients and carry out phenomenological modeling to study the phase transition and electrocaloric effect. The calculated phase diagram is in excellent quantitative agreement with experiments. Furthermore, we propose a new method based on effective internal electric field to simulate polarization in the macroscopic paraelectric state of ferroelectric relaxor. The computed composition and temperature-dependent entropy and temperature change induced by electrocaloric effect are in good agreement with the measured data available for single crystal.     

Effect of La2O3 on the microstructure and optical performance of (Tb0.8Y0.2-xLax)2O3 ceramics

(Tb_0.8Y_0.2-xLa_x)₂O₃ transparent ceramics were prepared by using co-precipitation method combined with pressure-less sintering in flowing H₂ atmosphere. Microstructure, optical transmittance, elements composition, and Verdet constant of the (Tb_0.8Y_0.2-xLa_x)₂O₃ ceramics were studied. The amount of La₂O₃ is crucial for the formation of expected transparent (Tb_0.8Y_0.2)₂O₃. With increasing content of La₂O₃, the number of pores and the grain size of as-fabricated (Tb_0.8Y_0.2-xLa_x)₂O₃ ceramics both decrease. When 4 at.% La₂O₃ is doped, the (Tb_0.8Y_0.16)₂O₃ transparent ceramics shows the highest transmittance of 73.3% at 1400 nm wavelength. With holding time increasing from 8 h to 15 h, the average grain size of (Tb_0.8Y_0.16La_0.04)₂O₃ ceramics gradually increases from 5 μm to 13 μm. The Verdet constant measured at 633 nm is ?352 rad/T·m, which is 2.63 times higher than that of TGG. In addition, large-size ceramics with Φ 20 mm × 3 mm and Φ 30 mm × 3 mm were also successfully obtained.     

Microwave-assisted polyol synthesis of sub-micrometer Y2O3 and Yb-Y2O3 particles for laser source application

Sub-micrometer powder (100–150 nm diameter) of Yb-doped yttrium oxide was obtained, for the first time, by microwave-assisted polyol (diethylene glycol, DEG) method. This method is based on fast and homogeneous increase of temperature, due to the microwave heating, and on addition of the hydrolysing agent (water) at high temperature. This promotes a fast nucleation followed by a controlled growth of nuclei. Different procedures were used to process the as-synthesized powders. In some cases washing by ultrapure water was used to dissolve nitrate and DEG by-products, this treatment allowed the use of a lower calcination temperature (150–200 °C less) to obtain the crystalline phase. Analysis of the calcined powder showed different levels of structures: from nanocrystal (10–15 nm), to primary particles (100–150 nm), to micrometer soft aggregates (2–4 μm). The microwave-assisted polyol method resulted an easy way to dope yttria with the desired amount of Yb³⁺. This work was carried out in order to prepare particles to be used as rare-earth doped Y₂O₃ and YAG polycrystalline transparent ceramic for laser source applications.     

Formation of bicontinuous,hydrophobic nylon 12 membranes via cold-solvent-induced phase separation for membrane distillation application

Skinless nylon 12 microporous membranes were prepared via a cold-solvent-induced phase-separation process from a binary nylon 12–formic acid system. Through the incorporation of an aging step, polymer nucleation in the dope was enhanced, and the formed membranes exhibited a special particulate structure composed of interlocked sticklike or sheaflike crystallites, which coexisted with continuous microporosity. The crystallite size was affected by the polymer concentration in the dope and the aging time; for example, aging alone allowed for the reduction of the particle diameter from about 20 μm to about 1 μm. Because the membranes were skinless and hydrophobic (contact angles ≈ 105°), they were potentially appropriate for desalination via membrane distillation (MDi). For the case of desalting 3.5% NaCl_(aq) by means of direct-contact MDi, very high rejection ratios (∼99.6%) were achieved for all membranes under the operation conditions (temperature of the hot stream = 50°C, temperature of the cold stream = 20°C, and circulation rate = 0.7 L/min), whereas the highest permeation flux obtainable was 5.15 L/m² h. The membranes were strong, with tensile strengths ranging from 4.7 to 6.3 N/mm². Finally, we discovered a shift from α to γ structure as the dope polymer increased, whereas the crystallinity was about 27% in all cases. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47036.     

Preparation and application evaluation of La2O3-doped Y2O3 crucible materials for melting TiAl alloys

A new La₂O₃-doped Y₂O₃ crucible materials was fabricated and evaluated by TiAl alloys melting test. Microstructure and properties of the La₂O₃-doped Y₂O₃ ceramics were systemically investigated. In addition, interfacial reaction mechanism of the La₂O₃-doped Y₂O₃ crucible materials and TiAl alloys, together with oxygen content of TiAl alloys were discussed. Solid solution of La³⁺ in the crystal lattice of Y₂O₃ significantly improved sintering properties of the La₂O₃-doped Y₂O₃ crucible materials and decreased the open porosity. Compared with pure Y₂O₃, when adding 15 wt% La₂O₃, the open porosity and strength retention ration after thermal shock test of the La₂O₃-doped Y₂O₃ crucible materials changed from 10.8% to 3.9% and from 64% to 78%, respectively. The interfacial reaction between La₂O₃-doped Y₂O₃ crucible materials and TiAl alloys belongs to physical dissolution, and no reaction products were found during the melting of TiAl alloys. When using the 15 wt% La₂O₃-doped Y₂O₃ crucible materials to melt TiAl alloys, oxygen content of the TiAl ingot declined to 530 ppm, which was only one fourth of that using pure Y₂O₃ materials.     

Effects of sintering temperature and Bi2O3, Y2O3 and MgO co-doping on the dielectric properties of X8R BaTiO3-based ceramics

Bi₂O₃, Y₂O₃ and MgO co-doped BaTiO₃ (BT)-based X8R ceramics were synthesized successfully for the first time. The effects of the sintering temperature and Bi₂O₃, Y₂O₃ and MgO dopants on the dielectric properties were investigated systematically. Bi₂O₃ doping can increase the Curie temperature (T_c), but reduces the overall dielectric permittivity. On the other hand, Y₂O₃ doping is beneficial to the formation of core-shell microstructure and the increase of T_c, whereas MgO can prevent excessive Y₂O₃ from diffusing into grain core, and thereby further contributes to the generation of the core–shell microstructure. The generation of the typical core-shell microstructure was confirmed and investigated in detail by using transmission electron microscopy (TEM). It is argued that the synergistic effects of Bi₂O₃, Y₂O₃ and MgO co-doping in terms of the formation of the core-shell structure and the increase of T_c, can help improve the temperature stability of the dielectric permittivity effectively. Increasing the sintering temperature leads to an increase in the grain size, which in turn leads to an increase in the overall dielectric permittivity due to the grain size effect.