JOURNAL OF ALLOYS AND COMPOUNDS
·
2021
·
IF 5.316
Sara Adeeba Ismail,Lulu Jiang,Peng Zhong,Truls Norby,Donglin Han
La 2 Ce 2 O 7 is known to be a disordered fluorite, i.e., 50% La-doped CeO 2 , exhibiting oxide ion conduction with contributions from protons in wet atmospheres and minority electrons under reducing conditions. Here, we report the effect of additional doping by partial substitution of La 3+ with divalent alkaline earth cations A 2+ ( A = Ca, Sr, Ba) on the hydration behavior and electrical conductivity of La 2 Ce 2 O 7 . A single-phase cubic fluorite structure was obtained for La 2 Ce 2 O 7 , (La 1- x Ca x ) 2 Ce 2 O 7-δ ( x = 0–0.3), (La 1- x Sr x ) 2 Ce 2 O 7-δ ( x = 0–0.2), and (La 1- x Ba x ) 2 Ce 2 O 7-δ ( x = 0–0.05). Substitution by A 2+ enhanced the degree of hydration, which may be attributed to increased concentration of hydratable oxygen vacancies and coordination of oxide ions by A 2+ in addition to La 3+ , while the basicity of the different A 2+ seemed unimportant. The doping increased ionic conductivity slightly, while the n-type electronic conductivity under reducing atmospheres increased considerably. XPS analyses indicated that the concentration and binding energy of Ce 3d electrons decreased with increasing doping level of Ca, implying an enhanced mobility of electrons which may be attributed to an observed decrease in lattice parameter .
研究领域:
材料科学
·
电化学
✓ 已验证
产品关联
DOI
高影响因子
JOURNAL OF NUCLEAR MATERIALS
·
2014
·
IF 2.016
Xin Wang,Kuo Jiang,Liang Zhou
Powders of (Nd 1− x Ce x ) 2 Zr 2 O 7+ y ( x = 0–1) with pyrochlore structure were prepared by sol-spray pyrolysis and subsequent graphite reduction at 1200 °C. The effects of cerium content on crystal structure, phase stability and microstructure of the (Nd 1− x Ce x ) 2 Zr 2 O 7+ y ( x = 0–1) inert matrix materials were studied. XRD and Raman results presented that all samples were in a single pyrochlore phase. XPS results indicated the cerium was in a single oxidation state of +4. After sintering at 1500 °C for 24 h in air, the sample of x = 1 underwent a phase segregation to Zr 1− x Ce x O 2 solid solutions of tetragonal, metastable tetragonal and cubic phases, the sample of x = 0.9 contained a few tetragonal phase in addition to fluorite phase, the samples of x = 0.5–0.8 had a single phase fluorite structure, the samples of x = 0–0.4 maintained the pyrochlore structure.
研究领域:
材料科学
·
无机化学
✓ 已验证
产品关联
DOI
高影响因子
CERAMICS INTERNATIONAL
·
2023
·
IF 5.2
Bo Ma,Zhiqin Wen,Jiedong Qin,Zhenyu Wu,Junxiao Liu,Yunming Lv,Junjie Yu,Yuhong Zhao
In this work, single-phase (Ce 0.2 Zr 0.2 La 0.2 Sm 0.2 Nd 0.2 )O 2-δ high-entropy fluorite oxides (HEFOs) were successfully prepared by conventional solid-phase reaction method and crystal structure and microstructure were studied in-depth. Single-phase (Ce 0.2 Zr 0.2 La 0.2 Sm 0.2 Nd 0.2 )O 2-δ is formed at 1600 °C for 12 h, and five cationic elements are uniformly distributed without any segregation at the micrometer and nanometer scales. And the XRD patterns with Rietveld refinement reveal the formation of single-phase fluorite structure of (Ce 0.2 Zr 0.2 La 0.2 Sm 0.2 Nd 0.2 )O 2-δ . The SAED patterns on the [0 1 ‾ 1] band axes are similar to the diffraction patterns of face-centered cubic fluorite structure, and the standard deviation of the cation radius (coordination VIII) distribution of the specimens is 0.1277, which is again identified as forming a single-phase fluorite structure. The bulk specimens are solid compacts free of obvious cracks with randomly distribution porosity at a rare level, and the powder specimens are irregular fragmented shapes with an average particles size of 5.41 μm. The average cation radius and interplanar spacings becomes larger compared with standard fluorite structure of CeO 2 due to the cation radius of La 3+ , Sm 3+ and Nd 3+ are larger than that of Ce 4+ , leading to an increase in lattice parameters of the HEFOs. In addition, the concentration of Ce 3+ in the Ce cation is only 8.1 %, and the δ -value is calculated to be 0.3081 based on the content of all cations per mole of the substance, which indicates that the composition of the prepared specimen is (Ce 0.2 Zr 0.2 La 0.2 Sm 0.2 Nd 0.2 )O 1.6919 .
研究领域:
材料科学
·
无机化学
✓ 已验证
产品关联
DOI
高影响因子
JOURNAL OF THE AMERICAN CERAMIC SOCIETY
·
2022
·Vol. 105
·期 8
·5490-5500
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IF 4.186
Liang Xu,Lei Su,Hongjie Wang,Min Niu,Lei Zhuang,Kang Peng,Xingyu Fan,Hongfei Gao,De Lu
Pursuing novel thermal barrier–coating materials with lower thermal conductivity and high-temperature stability can simultaneously improve the working efficiency and service temperature of a gas turbine. In this study, a series of high-entropy RE 2 (Y 0.2 Yb 0.2 Nb 0.2 Ta 0.2 Ce 0.2 ) 2 O 7 (RE = La, Nd, Sm, Gd, Dy, and Er) oxides were prepared though solid-state reaction. Through tuning the rare-earth cations, an order–disorder transition occurs from certain partially ordered weberite structure ( C 222 1 ) to disordered defective fluorite structure ( Fm 3 ¯ $\bar{3}$ m ). All the high-entropy RE 2 (Y 0.2 Yb 0.2 Nb 0.2 Ta 0.2 Ce 0.2 ) 2 O 7 oxides possess low thermal conductivity in the range of 0.91–1.34 W m −1 K −1 at room temperature, which can be attributed to increased lattice anharmonicity and disorder, resulting in additional phonon scattering. Herein, we proved that the incorporation of heterovalent cations at B-sites in high-entropy A 2 B 2 O 7 crystals is an effective strategy to reduce the thermal conductivity without compromising the decrease of oxygen vacancy. Moreover, the high-entropy RE 2 (Y 0.2 Yb 0.2 Nb 0.2 Ta 0.2 Ce 0.2 ) 2 O 7 oxides show the relatively higher thermal expansion coefficients of 10.3–10.7 × 10 −6 °C −1 and excellent phase stability at elevated temperatures.
研究领域:
材料科学
·
热力学
✓ 已验证
产品关联
DOI
高影响因子
CERAMICS INTERNATIONAL
·
2021
·
IF 4.527
Yubin Wen,Yufu Liu
Typical high-entropy fluorite oxides with five metal cations have exhibited improved thermomechanical properties . In this work, we have successfully prepared single-phase high-entropy (Zr 0.2 Ce 0.2 Hf 0.2 Y 0.2 Al 0.2 )O 2-δ fluorite oxides through the combination of sol-gel method and calcination , using metal nitrate/chloride, citric acid and absolute ethanol as the primary raw materials. A series of characterizations were employed for chemical, morphological and structural analysis of the calcined products. The five cationic elements were shown to be uniformly distributed in the nearly pure fluorite oxide without apparent segregation at the micro/nano-meter scales after 1500 °C calcination. Annealing and water quenching within the test temperature range did not witness any appreciable phase transition. It is revealed that the concentration of Ce 3+ in Ce ions reaches 33.84% and δ is equal to 0.234, yielding a nominal composition of (Zr 0.2 Ce 0.2 Hf 0.2 Y 0.2 Al 0.2 )O 1.766 . Cation and anion configurational entropy were found to be 1.609 R and 0.722 R, respectively, where R is the ideal gas constant, for a sum of the total configurational entropy of 2.331 R in the high-entropy system. Line defects inside the crystals and 3 types of crystalline boundary structures have been observed and identified among the mostly atomically sharp grain boundaries.
研究领域:
材料科学
·
化学
✓ 已验证
DOI
高影响因子
CORROSION SCIENCE
·
2023
·
IF 8.3
Liang Xu,Min Niu,Lei Su,Xin He,Haotian Ni,Hongfei Gao,Lei Zhuang,Hongjie Wang
Engineering stoichiometry of materials is an effective strategy to optimize the comprehensive properties. Here we prepare high-entropy Er 2 (Y 0.2 Yb 0.2 Nb 0.2 Ta 0.2 Ce x ) 2 O δ with single-phase fluorite structure by a solid-state reaction. The effects of stoichiometry of cerium on thermophysical properties and corrosion resistance to calcium−magnesium−alumina−silicate (CMAS) of the high-entropy oxides have been investigated. By engineering the cerium stoichiometry, thermal conductivity increases slightly from 1.21 to 1.36 W·m −1 ·K −1 and thermal expansion coefficients also increases from 10.56 × 10 −6 to 11.61 × 10 −6 °C −1 at 1000 °C. Furthermore, corrosion resistance of the high-entropy Er 2 (Nb 0.2 Ta 0.2 Y 0.2 Yb 0.2 Ce x ) 2 O δ improves with the increase of cerium content. The effects of cerium content on CMAS resistance have been discussed in detail. Our work reveals that engineering stoichiometry of high-entropy oxides is expected to be an effective strategy to broaden the compositional space and optimize the thermophysical properties and CMAS corrosion resistance.
研究领域:
材料科学
·
工程学
✓ 已验证
DOI
高影响因子
JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE
·
2025
·
IF 2
Zhang Dongbo,Tang Xinyue,Wang Ning,Xiao Mingwei,Yan Jiangrong,Zhang Yongsheng
High-entropy oxides used as thermal barrier coating materials have attracted considerable attention from scientific communities owing to their unique properties, such as low thermal conductivity and good stability at high temperatures. In this study, a new (La 0.2 Gd 0.2 Zr 0.2 Ce 0.2 Ho 0.2 )O 2-δ ((LGZCH)O) fluorite-structured high-entropy oxide was successfully synthesized through a solid-state reaction at 1400 °C. The resulting material demonstrated good phase stability after sintering at high temperatures. The microstructure, microscopic morphology, ionic valence, compositional distribution, optical properties, thermal conductivity, thermal expansion properties, and mechanical properties of (LGZCH)O were investigated. X-ray diffraction results showed that the (LGZCH)O fluorite-structured high-entropy oxide exhibited good stability during sintering at different temperatures with an optimum sintering temperature of 1580 °C. Ce 4+ converted to Ce 3+ at high temperatures. Scanning electron microscopy results showed that the material had a high porosity of approximately 28.9% after sintering at 1580 °C. (LGZCH)O had a higher infrared radiation emissivity of 82.2%-87.6% in the range of 2.5-6.0 μm indicating that it had better thermal radiation shielding performance. After porosity modification, the thermal conductivity ranged from 1.27 to 1.00 W m −1 K −1 from room temperature to 1000 °C, which is considerably lower than that of yttria-stabilized zirconia. Additionally, (LGZCH)O exhibited low coefficients of thermal expansion measuring 9.65 × 10 −6 K −1 and 10.13 × 10 −6 K −1 at 1000 and 1200 °C, respectively. The hardness and Young’s modulus of the bulk (LGZCH)O measured via nanoindentation tests were 8.86 GPa and 153.98 GPa, respectively, which are marginally inferior to those of YSZ. Therefore, (LGZCH)O can be considered a promising candidate material for thermal barrier coatings.
研究领域:
材料科学
·
能源工程
✓ 已验证
产品关联
DOI
高影响因子
JOURNAL OF THE AMERICAN CERAMIC SOCIETY
·
2023
·
IF 3.9
Yun Sun,Jiangtao Wu,Ying Tang,Huaicheng Xiang,Jie Li,Liang Fang
X-ray diffractometer with Rietveld refinement and Raman spectroscopy were used for phase analysis. Ca doping results in decreased ε r (24.09–21.52), Q × f (68 914–40 110 GHz), and τ f (−50.0 ppm/°C to −60.2 ppm/°C) all decrease, which obviously does not conform to the mutual constraint relationship among the three parameters of microwave dielectric properties. The ε r of Ce 1− x Ca x O 2− x ceramics is affected by the ion polarizability and the Ce rattling and valence states, among which the rattling of Ce cations plays a dominant role. The presence of oxygen vacancies in Ce 1− x Ca x O 2− x ceramics explains the decrease in Q × f . The τ ε , ε r , and α L are responsible for the decrease in τ f , especially for the τ αm -3 α L values.
研究领域:
材料科学
·
物理学
✓ 已验证
DOI
高影响因子
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