The rapid cooling of a metallic liquid(ML)results in short-range order(SRO)among the atomic arrangements and a disordered structure in the resulting metallic glass(MG).These phenomena cause various possible features i...The rapid cooling of a metallic liquid(ML)results in short-range order(SRO)among the atomic arrangements and a disordered structure in the resulting metallic glass(MG).These phenomena cause various possible features in the microscopic structure of the MG,presenting a puzzle about the nature of the MGs’microscopic structure beyond SRO.In this study,the nanoscale density gradient(NDG)originating from a sequential arrangement of clusters with different atomic packing densities(APDs),representing the medium-range structural heterogeneity in Zr_(60)Cu_(30)Al_(10)MG,was characterized using electron tomography(ET)combined with image simulations based on structure modeling.The coarse polyhedrons with distinct facets identified in the three-dimensional images coincide with icosahedron-like clusters and represent the spatial positions of clusters with high APDs.Rearrangements of the different clusters according to descending APD order in the glass-forming process are responsible for the NDG that stabilizes both the supercooled ML and the amorphous states and acts as a hidden rule in the transition from ML to MG.展开更多
Soft magnetic composites(SMCs)play a pivotal role in the development of high-frequency,miniaturization and complex forming of modern electronics.However,they usually suffer from a trade-off between high magnetization ...Soft magnetic composites(SMCs)play a pivotal role in the development of high-frequency,miniaturization and complex forming of modern electronics.However,they usually suffer from a trade-off between high magnetization and good magnetic softness(high permeability and low core loss).In this work,utilizing the order modulation strategy,a critical state in a FeSiBCCr amorphous soft magnetic composite(ASMC),consisting of massive crystal-like orders(CLOs,∼1 nm in size)with the feature ofα-Fe,is designed.This critical-state structure endows the amorphous powder with the enhanced ferromagnetic exchange interactions and the optimized magnetic domains with uniform orientation and fewer micro-vortex dots.Superior comprehensive soft magnetic properties at high frequency emerge in the ASMC,such as a high saturation magnetization(Ms)of 170 emu g^(-1)and effective permeability(µ_(e))of 65 combined with a core loss(Pcv)as low as 70 mW cm^(-3)(0.01 T,1 MHz).This study provides a new strategy for the development of high-frequency ASMCs,possessing suitable comprehensive soft magnetic performance to match the requirements of the modern magnetic devices used in the third-generation semiconductors and new energy fields.展开更多
Rare earth high-entropy alloys(RE-HEAs)exhibit great potential to be applied as refrigerants due to their good comprehensive magnetocaloric properties.In this work,octary GdTbDyHoErTmCoAl and GdTbDyHoErTmCoNi RE-HEAs ...Rare earth high-entropy alloys(RE-HEAs)exhibit great potential to be applied as refrigerants due to their good comprehensive magnetocaloric properties.In this work,octary GdTbDyHoErTmCoAl and GdTbDyHoErTmCoNi RE-HEAs with amorphous/nanocrystalline structure exhibiting comparable magnetocaloric effect were synthesized.Both RE-HEAs show a second-order magnetic phase transition in the temperature range of hydrogen liquefaction.Due to the complex magnetic interactions,a spin glasslike behavior at low temperatures is observed in the RE-HEAs.A superior magnetocaloric effect is obtained in the nanocrystalline GdTbDyHoErTmCoNi high-entropy alloy that is multiphase attributed to a stronger magnetic exchange interaction when compared with the other that exhibits single amorphous structure.Despite heterogeneous microstructure,homogeneous chemical distributions are observed in the partially crystallized high-entropy alloy.In addition,the magnetocaloric effect and magnetic transition behavior of rare earth medium-and high-entropy alloys,including the RE-HEAs in this study,are summarized and discussed.The results in this work provide a helpful guide for the design of RE-HEAs for hydrogen liquefaction applications with excellent magnetocaloric effects.展开更多
Metal borohydride ammoniates have become one of the most promising hydrogen storage materials due to their ultrahigh capacities.However,their application is still restricted by the high temperature of hydrogen desorpt...Metal borohydride ammoniates have become one of the most promising hydrogen storage materials due to their ultrahigh capacities.However,their application is still restricted by the high temperature of hydrogen desorption and the release of ammonia.Here,to promote the dehydrogenation evolution and suppress the ammonia release,different amounts of NbF 5 were introduced into Mg(BH4)2·2NH3.Compared to the pure Mg(BH_(4))_(2)·2NH_(3),the Mg(BH_(4))_(2)·2NH_(3)-NbF_(5) composites exhibit lower onset dehydriding temperatures(53–57℃)and higher dehydriding capacities(5.6 wt.%–8.2 wt.%)at below 200℃,with the complete suppression of ammonia.In addition,7.4 wt.%H_(2) could be released from Mg(BH_(4))_(2)·2NH_(3)–5 mol%NbF5 composite at 200℃ within 20 min and the apparent activation energy is calculated to be 60.28 kJ mol^(-1),which is much lower than that of pure Mg(BH_(4))_(2)·2NH_(3)(92.04 kJ mol^(-1)).Mg(BH_(4))_(2)·2NH_(3) should mechanochemically react with NbF5,forming dual-metal(Mg,Nb)borohydride ammoniate and spherical MgF2.The introduction of electronegative Nb cation results in-situ formation of(Mg,Nb)borohydride ammoniate towards a lower dehydrogenation temperature and a higher hydrogen release purity.The increased phase boundaries among the Mg(BH_(4))_(2)·2NH_(3),dual-metal(Mg,Nb)borohydride ammoniate,and MgF2 phases further facilitate the hydrogen diffusion during the dehydrogenation of the composites.展开更多
基金supported by the National Natural Science Foundation of China(51971093,52192603,and 51501043)。
文摘The rapid cooling of a metallic liquid(ML)results in short-range order(SRO)among the atomic arrangements and a disordered structure in the resulting metallic glass(MG).These phenomena cause various possible features in the microscopic structure of the MG,presenting a puzzle about the nature of the MGs’microscopic structure beyond SRO.In this study,the nanoscale density gradient(NDG)originating from a sequential arrangement of clusters with different atomic packing densities(APDs),representing the medium-range structural heterogeneity in Zr_(60)Cu_(30)Al_(10)MG,was characterized using electron tomography(ET)combined with image simulations based on structure modeling.The coarse polyhedrons with distinct facets identified in the three-dimensional images coincide with icosahedron-like clusters and represent the spatial positions of clusters with high APDs.Rearrangements of the different clusters according to descending APD order in the glass-forming process are responsible for the NDG that stabilizes both the supercooled ML and the amorphous states and acts as a hidden rule in the transition from ML to MG.
基金Guangdong Major Project of Basic and Applied Basic Research,China(Grant No.2019B030302010)the National Natural Science Foundation of China(Grant Nos.52301212,52071222,52101191,52001219)+1 种基金the National Key Research and Development Program of China(Grant No.2021YFA0716302)Guangdong Basic and Applied Basic Research,China(Grant Nos.2022A1515010347,2020B1515130007).
文摘Soft magnetic composites(SMCs)play a pivotal role in the development of high-frequency,miniaturization and complex forming of modern electronics.However,they usually suffer from a trade-off between high magnetization and good magnetic softness(high permeability and low core loss).In this work,utilizing the order modulation strategy,a critical state in a FeSiBCCr amorphous soft magnetic composite(ASMC),consisting of massive crystal-like orders(CLOs,∼1 nm in size)with the feature ofα-Fe,is designed.This critical-state structure endows the amorphous powder with the enhanced ferromagnetic exchange interactions and the optimized magnetic domains with uniform orientation and fewer micro-vortex dots.Superior comprehensive soft magnetic properties at high frequency emerge in the ASMC,such as a high saturation magnetization(Ms)of 170 emu g^(-1)and effective permeability(µ_(e))of 65 combined with a core loss(Pcv)as low as 70 mW cm^(-3)(0.01 T,1 MHz).This study provides a new strategy for the development of high-frequency ASMCs,possessing suitable comprehensive soft magnetic performance to match the requirements of the modern magnetic devices used in the third-generation semiconductors and new energy fields.
基金Project supported by the National Natural Science Foundation of China(52101193,51975183)China Postdoctoral Science Foundation(2022M711002)+2 种基金Fundamental Research Funds for the Central Universities(B220202036)the Natural Science Foundation of Jiangsu Province(BK20201316)Jiangsu Planned Projects for Postdoctoral Research Funds(2021K646C)。
文摘Rare earth high-entropy alloys(RE-HEAs)exhibit great potential to be applied as refrigerants due to their good comprehensive magnetocaloric properties.In this work,octary GdTbDyHoErTmCoAl and GdTbDyHoErTmCoNi RE-HEAs with amorphous/nanocrystalline structure exhibiting comparable magnetocaloric effect were synthesized.Both RE-HEAs show a second-order magnetic phase transition in the temperature range of hydrogen liquefaction.Due to the complex magnetic interactions,a spin glasslike behavior at low temperatures is observed in the RE-HEAs.A superior magnetocaloric effect is obtained in the nanocrystalline GdTbDyHoErTmCoNi high-entropy alloy that is multiphase attributed to a stronger magnetic exchange interaction when compared with the other that exhibits single amorphous structure.Despite heterogeneous microstructure,homogeneous chemical distributions are observed in the partially crystallized high-entropy alloy.In addition,the magnetocaloric effect and magnetic transition behavior of rare earth medium-and high-entropy alloys,including the RE-HEAs in this study,are summarized and discussed.The results in this work provide a helpful guide for the design of RE-HEAs for hydrogen liquefaction applications with excellent magnetocaloric effects.
基金supported by the National Key Research and Development Plan(Grant No.2021YFB3802400)the National Natural Science Foundation of China(Grant Nos.52071141,52271212,52201250)+1 种基金the Equipment Pre-research Field Foundation(Grant No.6140721040101)the Interdisciplinary Innovation Program of North China Electric Power University(Grant No.XM2112355).
文摘Metal borohydride ammoniates have become one of the most promising hydrogen storage materials due to their ultrahigh capacities.However,their application is still restricted by the high temperature of hydrogen desorption and the release of ammonia.Here,to promote the dehydrogenation evolution and suppress the ammonia release,different amounts of NbF 5 were introduced into Mg(BH4)2·2NH3.Compared to the pure Mg(BH_(4))_(2)·2NH_(3),the Mg(BH_(4))_(2)·2NH_(3)-NbF_(5) composites exhibit lower onset dehydriding temperatures(53–57℃)and higher dehydriding capacities(5.6 wt.%–8.2 wt.%)at below 200℃,with the complete suppression of ammonia.In addition,7.4 wt.%H_(2) could be released from Mg(BH_(4))_(2)·2NH_(3)–5 mol%NbF5 composite at 200℃ within 20 min and the apparent activation energy is calculated to be 60.28 kJ mol^(-1),which is much lower than that of pure Mg(BH_(4))_(2)·2NH_(3)(92.04 kJ mol^(-1)).Mg(BH_(4))_(2)·2NH_(3) should mechanochemically react with NbF5,forming dual-metal(Mg,Nb)borohydride ammoniate and spherical MgF2.The introduction of electronegative Nb cation results in-situ formation of(Mg,Nb)borohydride ammoniate towards a lower dehydrogenation temperature and a higher hydrogen release purity.The increased phase boundaries among the Mg(BH_(4))_(2)·2NH_(3),dual-metal(Mg,Nb)borohydride ammoniate,and MgF2 phases further facilitate the hydrogen diffusion during the dehydrogenation of the composites.