A novel sol-gel processing was developed to synthesize polycrystalline cerium-doped lutetium pyrosilicate （Lu2Si2O7Ce, LPS ：Ce） powders under low temperature. It was found that the addition of propylene oxide （PPO...A novel sol-gel processing was developed to synthesize polycrystalline cerium-doped lutetium pyrosilicate （Lu2Si2O7Ce, LPS ：Ce） powders under low temperature. It was found that the addition of propylene oxide （PPO） could promote the formation of Lu-O-Si bonds in precursor, which was beneficial to the formation of LPS phase. X-ray diffraction （XRD） patterns indicated that the single-phased LPS powder was well crystallized at 1050℃. Microstructure observation demonstrated that the synthetic LPS powder was composed of ellipsoidal grains with the mean size of 40 nm. The luminescent properties were characterized by photoluminescence （PL）, X-ray excited luminescence （XEL） and vacuum ultraviolet （VUV） spectroscopy at room temperature. The synthetic LPS：Ce powder emitted a broad emission spectrum centered at about 380 nm, which should be ascribed to the 5d→4f transition of Ce3＋. Decay time of the synthetic LPS：Ce powder was measured to be only 32 ns.展开更多
In this study,the water vapor corrosion resistance of two types of high-entropy pyrosilicates((Yb_(0.2)Y_(0.2)Lu_(0.2)Ho_(0.2)Er_(0.2))_(2)Si_(2)O_(7)((5RE1/5)_(2)Si_(2)O_(7))and(Yb_(0.2)5Lu_(0.2)5Ho_(0.2)5Er_(0.2)5)_...In this study,the water vapor corrosion resistance of two types of high-entropy pyrosilicates((Yb_(0.2)Y_(0.2)Lu_(0.2)Ho_(0.2)Er_(0.2))_(2)Si_(2)O_(7)((5RE1/5)_(2)Si_(2)O_(7))and(Yb_(0.2)5Lu_(0.2)5Ho_(0.2)5Er_(0.2)5)_(2)Si_(2)O_(7)((4RE_(1/4))_(2)Si_(2)O_(7)))and two single-component pyrosilicates(Yb_(2)Si_(2)O_(7) and Lu_(2)Si_(2)O_(7))were evaluated at 1350℃ for 50e100 h,and the initial corrosion behaviors of these pyrosilicates were studied.The results showed that the final corrosion products of the four types of pyrosilicates were all X2-type monosilicates,exhibiting similar corrosion phenomena.However,(4RE_(1/4))_(2)Si_(2)O_(7) generated many nanoscale monosilicate grains during corrosion.The corrosion resistance of Lu_(2)Si_(2)O_(7) was clearly better than those of the others,and(4RE_(1/4))_(2)Si_(2)O_(7) exhibited the worst corrosion resistance.The corrosion mechanism of the pyrosilicate blocks was analyzed from the perspectives of grain size,bulk hydrophobicity,and binding energy.This study potentially provides a theoretical basis for the preparation of high-entropy pyrosilicates with different atomic ratios according to the different properties of the various rare earth elements.展开更多
High-entropy pyrosilicate element selection is relatively blind, and the thermal expansion coefficient (CTE) of traditional β-type pyrosilicate is not adjustable, making it difficult to meet the requirements of vario...High-entropy pyrosilicate element selection is relatively blind, and the thermal expansion coefficient (CTE) of traditional β-type pyrosilicate is not adjustable, making it difficult to meet the requirements of various types of ceramic matrix composites (CMCs). The following study aimed to develop a universal rule for high-entropy pyrosilicate element selection and to achieve directional control of the thermal expansion coefficient of high-entropy pyrosilicate. The current study investigates a high-entropy design method for obtaining pyrosilicates with stable β-phase and γ-phase by introducing various rare-earth (RE) cations. The solid-phase method was used to create 12 different types of high-entropy pyrosilicates with 4–6 components. The high-entropy pyrosilicates gradually transformed from β-phase to γ-phase with an increase in the average radius of RE^(3+) ions ( r¯(RE^(3+))). The nine pyrosilicates with a small r¯(RE^(3+)) preserve β-phase or γ-phase stability at room temperature to the maximum of 1400 ℃. The intrinsic relationship between the thermal expansion coefficient, phase structure, and RE–O bond length has also been found. This study provides the theoretical background for designing high-entropy pyrosilicates from the perspective of r¯(RE^(3+)). The theoretical guidance makes it easier to synthesize high-entropy pyrosilicates with stable β-phase or γ-phase for the use in environmental barrier coatings (EBCs). The thermal expansion coefficient of γ-type high-entropy pyrosilicate can be altered through component design to match various types of CMCs.展开更多
Eu2+ activated pyrosilicate phosphor were prepared under a reducing atmosphere by solid-state reaction.The crystal structure of Ba2 MgSi2 O7: Eu2+ was analyzed by XRD method.The excitation spectrum of Ba2MgSi2 O7; Eu2...Eu2+ activated pyrosilicate phosphor were prepared under a reducing atmosphere by solid-state reaction.The crystal structure of Ba2 MgSi2 O7: Eu2+ was analyzed by XRD method.The excitation spectrum of Ba2MgSi2 O7; Eu2+ is composed of two broad bands centered at about 310 nm and 395 nm respectively.In the emission spectra, the peak wavelength is at about 507 nm under 380 nm UV excitation.It was found that the introduction of Zn2+ into Ba2MgSi2O7: Eu2+ Can effectively increase its emission intensity without changing the position of emission peak.And the Eu2 + and Ce3 + codoped pyrosilicate phosphor is the efficient bluish green phosphor under the excitation of long UV light and its emission intensity is stronger than Eu2+ doped pyrosilicate phosphor.展开更多
A new phase of dibarium copper disilicate, b-Ba2CuSi2O7, was obtained by the solid-state reaction. Crystal data: Mr = 506.4, tetragonal, P421m, a = 8.284(2), c = 5.313(3) ? V = 364.6(4) ?, Z = 2, Dc = 4.61 g/cm3, l(Mo...A new phase of dibarium copper disilicate, b-Ba2CuSi2O7, was obtained by the solid-state reaction. Crystal data: Mr = 506.4, tetragonal, P421m, a = 8.284(2), c = 5.313(3) ? V = 364.6(4) ?, Z = 2, Dc = 4.61 g/cm3, l(MoKa) = 0.71703 ? ?= 13.91 mm-1, F(000) = 450 and T = 293(2) K; the final R = 0.0343, wR = 0.0382 and S = 1.02 for 512 observed reflections (I > 3s(I)) refined by 34 variables. The compound was characterized by a layered structure composed of CuO4 tetrahedra and Si2O7 anions with the Ba cations filling the cavities between the layers. The building blocks of the present structure are similar to those in the a-Ba2CuSi2O7, but the linkage of CuO4 tetrahedra and Si2O7 anions is significantly different. In particular, the double-tetrahedral anions of Si2O76- form an orthogonal arrangement in the present structure, in contrast to the parallel arrangement reported in the a-Ba2CuSi2O7.展开更多
Single crystal of Lu2Si2OT：Pr was grown by Czochralski method. Transmittance, photoluminescence excitation （PLE） and photo- luminescence （PL） spectra, X-ray excited luminescence （XEL） and fluorescence decay tim...Single crystal of Lu2Si2OT：Pr was grown by Czochralski method. Transmittance, photoluminescence excitation （PLE） and photo- luminescence （PL） spectra, X-ray excited luminescence （XEL） and fluorescence decay time spectra of the sample were measured and dis- cussed to investigate its optical characteristics. The crystal structure of the as grown Lu2Si207：Pr was confirmed to be C2/m. There was a broad absorption peaking at 245 um in the region from 200-260 urn. The PL spectntm was dominated by fast 3py^3Hj band peaking at 524 nm. The XEL spectrum was dominated by the fast 5d14t^---~41e emission peaking at 265 nm. The 2D （temperature-intensity） and 3D （tem- perature-wavelength-intensity） thermally stimulated luminescence （TSL） spectra were measured. The Pr3＋ ion was found to be the recombina- tion center during the TSL process. Three obvious traps were detected in LPS：Pr single crystal with energy depth at 1.06, 0.78 and 0.67 eV.展开更多
In an attempt to synthesize the homologous sulfide of KHo2CuSe4 by using KBr as flux in a sealed evacuated quartz tube, transparent crystals of Ho4S3Si2O7 (Mr = 924.08) were isolated. The crystal structure of Ho4S3Si2...In an attempt to synthesize the homologous sulfide of KHo2CuSe4 by using KBr as flux in a sealed evacuated quartz tube, transparent crystals of Ho4S3Si2O7 (Mr = 924.08) were isolated. The crystal structure of Ho4S3Si2O7 was determined by single-crystal X-ray diffraction method. Ho4S3Si2O7 crystallizes in a tetragonal system, space group I41/amd (No. 141) with a = 11.666(4), c = 13.593(5) ? V = 1850(2) ?, Z = 8, Dc = 6.64g/cm3, F(000)= 3200, m(MoKa) = 34.79mm-1, final R = 0.0355 and Rw = 0.0378 for 851 reflections with I > 3s(I). The structure of Ho4S3Si2O7 contains two crystallographically independent Ho3+ cations that are interconnected by S2 anions and the isolated [Si2O7]6 units. Ho(1) is coordinated by three O atoms and three S atoms to form a trigonal prismatic geometry, while Ho(2) is coordinated by six O atoms and three S atoms to form a tricapped trigonal prismatic geometry. The Si2O7 double tetrahedra are in the eclipsed configuration with non-linear SiOSi bridges (angle : 129.2(9)).展开更多
基金supported by the National Natural Science Foundation of China(Grant No.51172139)
文摘A novel sol-gel processing was developed to synthesize polycrystalline cerium-doped lutetium pyrosilicate （Lu2Si2O7Ce, LPS ：Ce） powders under low temperature. It was found that the addition of propylene oxide （PPO） could promote the formation of Lu-O-Si bonds in precursor, which was beneficial to the formation of LPS phase. X-ray diffraction （XRD） patterns indicated that the single-phased LPS powder was well crystallized at 1050℃. Microstructure observation demonstrated that the synthetic LPS powder was composed of ellipsoidal grains with the mean size of 40 nm. The luminescent properties were characterized by photoluminescence （PL）, X-ray excited luminescence （XEL） and vacuum ultraviolet （VUV） spectroscopy at room temperature. The synthetic LPS：Ce powder emitted a broad emission spectrum centered at about 380 nm, which should be ascribed to the 5d→4f transition of Ce3＋. Decay time of the synthetic LPS：Ce powder was measured to be only 32 ns.
基金This work is supported by the National Key Technologies R&D Program of China(No.2018YFB0704400)Shanghai Technical Platform for Testing on Inorganic Materials(No.19DZ2290700).
文摘In this study,the water vapor corrosion resistance of two types of high-entropy pyrosilicates((Yb_(0.2)Y_(0.2)Lu_(0.2)Ho_(0.2)Er_(0.2))_(2)Si_(2)O_(7)((5RE1/5)_(2)Si_(2)O_(7))and(Yb_(0.2)5Lu_(0.2)5Ho_(0.2)5Er_(0.2)5)_(2)Si_(2)O_(7)((4RE_(1/4))_(2)Si_(2)O_(7)))and two single-component pyrosilicates(Yb_(2)Si_(2)O_(7) and Lu_(2)Si_(2)O_(7))were evaluated at 1350℃ for 50e100 h,and the initial corrosion behaviors of these pyrosilicates were studied.The results showed that the final corrosion products of the four types of pyrosilicates were all X2-type monosilicates,exhibiting similar corrosion phenomena.However,(4RE_(1/4))_(2)Si_(2)O_(7) generated many nanoscale monosilicate grains during corrosion.The corrosion resistance of Lu_(2)Si_(2)O_(7) was clearly better than those of the others,and(4RE_(1/4))_(2)Si_(2)O_(7) exhibited the worst corrosion resistance.The corrosion mechanism of the pyrosilicate blocks was analyzed from the perspectives of grain size,bulk hydrophobicity,and binding energy.This study potentially provides a theoretical basis for the preparation of high-entropy pyrosilicates with different atomic ratios according to the different properties of the various rare earth elements.
基金supported by the Instrument and Equipment Development,Chinese Academy of Sciences(YJKYYQ20210030)Shanghai Science and Technology Innovation Action Plan(21142201100).
文摘High-entropy pyrosilicate element selection is relatively blind, and the thermal expansion coefficient (CTE) of traditional β-type pyrosilicate is not adjustable, making it difficult to meet the requirements of various types of ceramic matrix composites (CMCs). The following study aimed to develop a universal rule for high-entropy pyrosilicate element selection and to achieve directional control of the thermal expansion coefficient of high-entropy pyrosilicate. The current study investigates a high-entropy design method for obtaining pyrosilicates with stable β-phase and γ-phase by introducing various rare-earth (RE) cations. The solid-phase method was used to create 12 different types of high-entropy pyrosilicates with 4–6 components. The high-entropy pyrosilicates gradually transformed from β-phase to γ-phase with an increase in the average radius of RE^(3+) ions ( r¯(RE^(3+))). The nine pyrosilicates with a small r¯(RE^(3+)) preserve β-phase or γ-phase stability at room temperature to the maximum of 1400 ℃. The intrinsic relationship between the thermal expansion coefficient, phase structure, and RE–O bond length has also been found. This study provides the theoretical background for designing high-entropy pyrosilicates from the perspective of r¯(RE^(3+)). The theoretical guidance makes it easier to synthesize high-entropy pyrosilicates with stable β-phase or γ-phase for the use in environmental barrier coatings (EBCs). The thermal expansion coefficient of γ-type high-entropy pyrosilicate can be altered through component design to match various types of CMCs.
基金Project supported by the National Natural Foundation of China (59982001)and Natural Science Foundation of Beijing(4012010)
文摘Eu2+ activated pyrosilicate phosphor were prepared under a reducing atmosphere by solid-state reaction.The crystal structure of Ba2 MgSi2 O7: Eu2+ was analyzed by XRD method.The excitation spectrum of Ba2MgSi2 O7; Eu2+ is composed of two broad bands centered at about 310 nm and 395 nm respectively.In the emission spectra, the peak wavelength is at about 507 nm under 380 nm UV excitation.It was found that the introduction of Zn2+ into Ba2MgSi2O7: Eu2+ Can effectively increase its emission intensity without changing the position of emission peak.And the Eu2 + and Ce3 + codoped pyrosilicate phosphor is the efficient bluish green phosphor under the excitation of long UV light and its emission intensity is stronger than Eu2+ doped pyrosilicate phosphor.
基金the Innovative Project (No.IP01007) and Hundred-Talent Program (No. 990168) of the Chinese Academy of Sciences
文摘A new phase of dibarium copper disilicate, b-Ba2CuSi2O7, was obtained by the solid-state reaction. Crystal data: Mr = 506.4, tetragonal, P421m, a = 8.284(2), c = 5.313(3) ? V = 364.6(4) ?, Z = 2, Dc = 4.61 g/cm3, l(MoKa) = 0.71703 ? ?= 13.91 mm-1, F(000) = 450 and T = 293(2) K; the final R = 0.0343, wR = 0.0382 and S = 1.02 for 512 observed reflections (I > 3s(I)) refined by 34 variables. The compound was characterized by a layered structure composed of CuO4 tetrahedra and Si2O7 anions with the Ba cations filling the cavities between the layers. The building blocks of the present structure are similar to those in the a-Ba2CuSi2O7, but the linkage of CuO4 tetrahedra and Si2O7 anions is significantly different. In particular, the double-tetrahedral anions of Si2O76- form an orthogonal arrangement in the present structure, in contrast to the parallel arrangement reported in the a-Ba2CuSi2O7.
基金Project supported by National Natural Science Foundation of China(50902145,51171239)the Natural Science Foundation of Shanghai(09ZR1435800)the Knowledge Innovation Program of the Chinese Academy of Sciences(SCX200701)
文摘Single crystal of Lu2Si2OT：Pr was grown by Czochralski method. Transmittance, photoluminescence excitation （PLE） and photo- luminescence （PL） spectra, X-ray excited luminescence （XEL） and fluorescence decay time spectra of the sample were measured and dis- cussed to investigate its optical characteristics. The crystal structure of the as grown Lu2Si207：Pr was confirmed to be C2/m. There was a broad absorption peaking at 245 um in the region from 200-260 urn. The PL spectntm was dominated by fast 3py^3Hj band peaking at 524 nm. The XEL spectrum was dominated by the fast 5d14t^---~41e emission peaking at 265 nm. The 2D （temperature-intensity） and 3D （tem- perature-wavelength-intensity） thermally stimulated luminescence （TSL） spectra were measured. The Pr3＋ ion was found to be the recombina- tion center during the TSL process. Three obvious traps were detected in LPS：Pr single crystal with energy depth at 1.06, 0.78 and 0.67 eV.
基金Supported by the Director Fund of Fujian Institute of Research on the Structure of Matter (No. 200196).
文摘In an attempt to synthesize the homologous sulfide of KHo2CuSe4 by using KBr as flux in a sealed evacuated quartz tube, transparent crystals of Ho4S3Si2O7 (Mr = 924.08) were isolated. The crystal structure of Ho4S3Si2O7 was determined by single-crystal X-ray diffraction method. Ho4S3Si2O7 crystallizes in a tetragonal system, space group I41/amd (No. 141) with a = 11.666(4), c = 13.593(5) ? V = 1850(2) ?, Z = 8, Dc = 6.64g/cm3, F(000)= 3200, m(MoKa) = 34.79mm-1, final R = 0.0355 and Rw = 0.0378 for 851 reflections with I > 3s(I). The structure of Ho4S3Si2O7 contains two crystallographically independent Ho3+ cations that are interconnected by S2 anions and the isolated [Si2O7]6 units. Ho(1) is coordinated by three O atoms and three S atoms to form a trigonal prismatic geometry, while Ho(2) is coordinated by six O atoms and three S atoms to form a tricapped trigonal prismatic geometry. The Si2O7 double tetrahedra are in the eclipsed configuration with non-linear SiOSi bridges (angle : 129.2(9)).
