Fine grains and slow grain growth rate are beneficial to preventing the thermal stress-induced cracking and thermal conductivity increase of thermal barrier coatings.Inspired by the sluggish diffusion effect of high-e...Fine grains and slow grain growth rate are beneficial to preventing the thermal stress-induced cracking and thermal conductivity increase of thermal barrier coatings.Inspired by the sluggish diffusion effect of high-entropy materials,a novel high-entropy(HE)rare-earth zirconate solid solution(La0.2Ce0.2Nd0.2Sm0.2Eu0.2)2 Zr2 O7 was designed and successfully synthesized in this work.The as-synthesized(La0.2Ce0.2Nd0.2Sm0.2Eu0.2)2 Zr2 O7 is phase-pure with homogeneous rare-earth element distribution.The thermal conductivity of as-synthesized(La0.2Ce0.2Nd0.2Sm0.2Eu0.2)2 Zr2 O7 at room temperature is as low as 0.76 W m^-1 K^-1.Moreover,after being heated at 1500℃for 1-18 h,the average grain size of(La0.2Ce0.2Nd0.2Sm0.2Eu0.2)2 Zr2 O7 only increases from 1.69μm to 3.92μm,while the average grain size of La2Zr2O7 increases from 1.96μm to 8.89μm.Low thermal conductivity and sluggish grain growth rate indicate that high-entropy(La0.2Ce0.2Nd0.2Sm0.2Eu0.2)2Zr2O7 is suitable for application as a thermal barrier coating material and it may possess good thermal stress-induced cracking resistance.展开更多
In situ high pressure energy dispersive X-ray diffraction measurements on layered perovskite-like manganate Ca3Mn2O7 under pressures up to 35 GPa have been Performed by using diamond anvil cell with synchrotron radiat...In situ high pressure energy dispersive X-ray diffraction measurements on layered perovskite-like manganate Ca3Mn2O7 under pressures up to 35 GPa have been Performed by using diamond anvil cell with synchrotron radiation.The results show that the structure of layered perovskite-like manganate Ca3Mn2O7 is unstable under pressure due to the easy compression of NaCl-type blocks.The structure of Ca3Mn2O7 underwent two phase transitions under pressures in the range of 0-35GPa.One was at about 1.3GPa with the crystal structure changing from tetragonalt go orthorhombic.The other was at about 9.5GPa with the crystal structure changing form orthorhombic back to another tetragonal.展开更多
Rare earth europium（Eu（3＋））-doped lithium tetraborate（Eu：Li_2B_4O_7） crystal is grown from its stoichiometric melt by microtube Czochralski pulling technique（μT-Cz） for the first time. The grown crystals ar...Rare earth europium（Eu（3＋））-doped lithium tetraborate（Eu：Li_2B_4O_7） crystal is grown from its stoichiometric melt by microtube Czochralski pulling technique（μT-Cz） for the first time. The grown crystals are subjected to powder x-ray diffraction（PXRD） analysis which reveals the tetragonal crystal structure of the crystals. UV–vis–NIR spectral analysis is carried out to study the optical characteristics of the grown crystals. The crystal is transparent in the entire visible region, and the lower cutoff is observed to be at 304 nm. The existence of BO_3 and BO_4 bonding structure and the molecular associations are analyzed by Fourier transform infrared（FTIR） spectroscopy. The results of excitation and emission-photoluminescence spectra of europium ion incorporated in lithium tetraborate（LTB） single crystal reveal that the observations of peaks at 258,297, and 318 nm in the excitation spectra and peaks at 579, 591, 597, 613, and 651 nm are observed in the emission spectra.The chromaticity coordinates are calculated from the emission spectra, and the emission intensity of the grown crystal is characterized through a CIE 1931（Commission International d＇Eclairage） color chromaticity diagram.展开更多
The noncentrosymmetricity of a prototypical correlated electron system Ca3Ru2O7 renders extensive interest in the possible polar metallic state,along with multiple other closely competing interactions.However,the stru...The noncentrosymmetricity of a prototypical correlated electron system Ca3Ru2O7 renders extensive interest in the possible polar metallic state,along with multiple other closely competing interactions.However,the structural domain formation in this material often complicates the study of intrinsic material properties.It is crucial to fully characterize the structural domains for unrevealing underlying physics.Here,we report the domain imaging on Ca3Ru2O7 crystal using the reflection of polarized light at normal incidence.The reflection anisotropy measurement utilizes the relative orientation between electric field component of the incident polarized light and the principal axis of the crystal,and gives rise to a peculiar contrast.The domain walls are found to be the interfaces between 90° rotated twin crystals by complementary magnetization measurements.A distinct contrast in reflectance is also found in the opposite cleavage surfaces,owing to the polar mode of the RuO6 octahedra.More importantly,the analysis of the contrast between all inequivalent cleavage surfaces enables a direct determination of the crystallographic orientation of each domain.Such an approach provides an efficient yet feasible method for structural domain characterization,which can also find applications in noncentrosymmetric crystals in general.展开更多
冰是自然界中最重要且分布最广泛的固体之一,在气候调节、生态系统维系及人类生产生活中发挥着不可替代的作用。然而,其微观结构及结晶、相变、缺陷行为等过程中的动力学机制仍有待深入揭示。透射电子显微镜(transmission electron micr...冰是自然界中最重要且分布最广泛的固体之一,在气候调节、生态系统维系及人类生产生活中发挥着不可替代的作用。然而,其微观结构及结晶、相变、缺陷行为等过程中的动力学机制仍有待深入揭示。透射电子显微镜(transmission electron microscopy,TEM)具备原子级成像和谱学分析能力,是研究冰的微观结构与动态行为的有力工具。然而,冰对电子束极为敏感,且在镜筒高真空环境中易发生升华,这些特性严重限制了常规TEM技术在冰表征中的适用性。本文系统回顾了冰的微观结构及早期TEM在该领域中的基础应用,接着综述了近年来由于低剂量成像技术与原位电镜技术的发展,冰的分子级成像和微观动力学研究的代表性进展,并展望了透射电镜在未来冰科学研究中的应用前景。本文旨在为深入理解冰的微观机制提供新的技术路径与研究视角。展开更多
基金financially supported by the National Natural Science Foundation of China (Nos.51672064 and U1435206)
文摘Fine grains and slow grain growth rate are beneficial to preventing the thermal stress-induced cracking and thermal conductivity increase of thermal barrier coatings.Inspired by the sluggish diffusion effect of high-entropy materials,a novel high-entropy(HE)rare-earth zirconate solid solution(La0.2Ce0.2Nd0.2Sm0.2Eu0.2)2 Zr2 O7 was designed and successfully synthesized in this work.The as-synthesized(La0.2Ce0.2Nd0.2Sm0.2Eu0.2)2 Zr2 O7 is phase-pure with homogeneous rare-earth element distribution.The thermal conductivity of as-synthesized(La0.2Ce0.2Nd0.2Sm0.2Eu0.2)2 Zr2 O7 at room temperature is as low as 0.76 W m^-1 K^-1.Moreover,after being heated at 1500℃for 1-18 h,the average grain size of(La0.2Ce0.2Nd0.2Sm0.2Eu0.2)2 Zr2 O7 only increases from 1.69μm to 3.92μm,while the average grain size of La2Zr2O7 increases from 1.96μm to 8.89μm.Low thermal conductivity and sluggish grain growth rate indicate that high-entropy(La0.2Ce0.2Nd0.2Sm0.2Eu0.2)2Zr2O7 is suitable for application as a thermal barrier coating material and it may possess good thermal stress-induced cracking resistance.
文摘In situ high pressure energy dispersive X-ray diffraction measurements on layered perovskite-like manganate Ca3Mn2O7 under pressures up to 35 GPa have been Performed by using diamond anvil cell with synchrotron radiation.The results show that the structure of layered perovskite-like manganate Ca3Mn2O7 is unstable under pressure due to the easy compression of NaCl-type blocks.The structure of Ca3Mn2O7 underwent two phase transitions under pressures in the range of 0-35GPa.One was at about 1.3GPa with the crystal structure changing from tetragonalt go orthorhombic.The other was at about 9.5GPa with the crystal structure changing form orthorhombic back to another tetragonal.
基金Project supported by the Department of Science and Technology–Science and Engineering Research Board(Grant No.SR/S2/LOP-0012/2011)the Government of India for Awarding Major Research Project,the University Grants Commission–Department of Atomic Research–Consortium for Scientific Research(Grant No.CSR–KN/CSR–63/2014–2015/503)the Kalpakkam and Indore,India
文摘Rare earth europium（Eu（3＋））-doped lithium tetraborate（Eu：Li_2B_4O_7） crystal is grown from its stoichiometric melt by microtube Czochralski pulling technique（μT-Cz） for the first time. The grown crystals are subjected to powder x-ray diffraction（PXRD） analysis which reveals the tetragonal crystal structure of the crystals. UV–vis–NIR spectral analysis is carried out to study the optical characteristics of the grown crystals. The crystal is transparent in the entire visible region, and the lower cutoff is observed to be at 304 nm. The existence of BO_3 and BO_4 bonding structure and the molecular associations are analyzed by Fourier transform infrared（FTIR） spectroscopy. The results of excitation and emission-photoluminescence spectra of europium ion incorporated in lithium tetraborate（LTB） single crystal reveal that the observations of peaks at 258,297, and 318 nm in the excitation spectra and peaks at 579, 591, 597, 613, and 651 nm are observed in the emission spectra.The chromaticity coordinates are calculated from the emission spectra, and the emission intensity of the grown crystal is characterized through a CIE 1931（Commission International d＇Eclairage） color chromaticity diagram.
基金Supported by the National Key Research and Development Program of China(Grant Nos.2019YFA0308602 and 2016YFA0300500)the National Natural Science Foundation of China(Grant Nos.11804220,11774305 and 11974237)Natural Science Foundation of Shanghai(Grant No.20ZR1428900).
文摘The noncentrosymmetricity of a prototypical correlated electron system Ca3Ru2O7 renders extensive interest in the possible polar metallic state,along with multiple other closely competing interactions.However,the structural domain formation in this material often complicates the study of intrinsic material properties.It is crucial to fully characterize the structural domains for unrevealing underlying physics.Here,we report the domain imaging on Ca3Ru2O7 crystal using the reflection of polarized light at normal incidence.The reflection anisotropy measurement utilizes the relative orientation between electric field component of the incident polarized light and the principal axis of the crystal,and gives rise to a peculiar contrast.The domain walls are found to be the interfaces between 90° rotated twin crystals by complementary magnetization measurements.A distinct contrast in reflectance is also found in the opposite cleavage surfaces,owing to the polar mode of the RuO6 octahedra.More importantly,the analysis of the contrast between all inequivalent cleavage surfaces enables a direct determination of the crystallographic orientation of each domain.Such an approach provides an efficient yet feasible method for structural domain characterization,which can also find applications in noncentrosymmetric crystals in general.
文摘冰是自然界中最重要且分布最广泛的固体之一,在气候调节、生态系统维系及人类生产生活中发挥着不可替代的作用。然而,其微观结构及结晶、相变、缺陷行为等过程中的动力学机制仍有待深入揭示。透射电子显微镜(transmission electron microscopy,TEM)具备原子级成像和谱学分析能力,是研究冰的微观结构与动态行为的有力工具。然而,冰对电子束极为敏感,且在镜筒高真空环境中易发生升华,这些特性严重限制了常规TEM技术在冰表征中的适用性。本文系统回顾了冰的微观结构及早期TEM在该领域中的基础应用,接着综述了近年来由于低剂量成像技术与原位电镜技术的发展,冰的分子级成像和微观动力学研究的代表性进展,并展望了透射电镜在未来冰科学研究中的应用前景。本文旨在为深入理解冰的微观机制提供新的技术路径与研究视角。
