The RMn_(2)O_(5) manganite compounds represent one class of multiferroic family with magnetic origins,which has been receiving continuous attention in the past decade.So far,our understanding of the magnetic origins f...The RMn_(2)O_(5) manganite compounds represent one class of multiferroic family with magnetic origins,which has been receiving continuous attention in the past decade.So far,our understanding of the magnetic origins for ferroelectricity in RMn_(2)O_(5) is associated with the nearly collinear antiferromagnetic structure of Mn ions,while the exchange striction induced ionic displacements are the consequence of the spin frustration competitions.While this scenario may be applied to almost all RMn_(2)O_(5) members,its limitation is either clear:the temperature-dependent behaviors of electric polarization and its responses to external stimuli are seriously materials dependent.These inconsistences raise substantial concern with the state-of-the-art physics of ferroelectricity in RMn_(2)O_(5).In this mini-review,we present our recent experimental results on the roles of the 4f moments from R ions which are intimately coupled with the 3d moments from Mn ions.DyMn_(2)O_(5) is a golden figure for illustrating these roles.It is demonstrated that the spin structure accommodates two nearly collinear sublattices which generate respectively two ferroelectric(FE)sublattices,enabling DyMn_(2)O_(5) an emergent ferrielectric(FIE)system rarely identified in magnetically induced FEs.The evidence is presented from several aspects,including FIE-like phenomena and magnetoelectric responses,proposed structural model,and experimental check by nonmagnetic substitutions of the 3d and 4f moments.Additional perspectives regarding possible challenges in understanding the multiferroicity of RMn_(2)O_(5) as a generalized scenario are discussed.展开更多
Using a stiffness matrix method, we in- vestigate the propagation behaviors of elastic waves in one-dimensional （1D） piezoelectric/piezomagnetic （PE/PM） phononic crystals （PCs） with line defects by calculating e...Using a stiffness matrix method, we in- vestigate the propagation behaviors of elastic waves in one-dimensional （1D） piezoelectric/piezomagnetic （PE/PM） phononic crystals （PCs） with line defects by calculating energy reflection/transmittion coefficients of quasi-pressure and quasi-shear waves. Line defects are created by the re- placement of PE or PM constituent layer. The defect modes existing in the first gap are considered and the influences on defect modes of the material properties and volume fraction of the defect layers, the type of incident waves, the location of defect layer and the number of structural layers are discussed in detail. Numerical results indicate that defect modes are the most obvious when the defect layers are inserted in the middle of the perfect PCs; the types of incidence wave and material properties of the defect layers have important effects on the numbers, the location of frequencies and the peaks of defect modes, and the defect modes are strongly de- pendent on volume fraction of the defect layers. We hope this paper will be found useful for the design of PE/PM acoustic filters or acoustic transducer with PCs structures.展开更多
The functionalities of hydrogel-based smart materials are highly related to the electrostatic interactions and molecular polarization associated with the polymer networks and encapsulated water droplets,and therefore ...The functionalities of hydrogel-based smart materials are highly related to the electrostatic interactions and molecular polarization associated with the polymer networks and encapsulated water droplets,and therefore the dielectric responses of the polarizable molecules in the polymer,water,and polymer-water interfaces are particularly attractive,where the properties of polymer-water interfacial molecules remain elusive.Different from extensive dielectric relaxation spectroscopy studies on polymer hydrogel solutions,in this work we investigate the dielectric response of chitosan hydrogels below the water solidifying point(ice-hydrogels)so that the contribution of chitosan-water interfacial molecules can be isolated.It is revealed that the chitosan-water interfacial polarizable molecules have slow dielectric relaxation but large polarization compared with the chitosan chains and water molecules,and the dielectric relaxations beyond~10^(4)Hz are substantially weak.The thermal activation energy of the dielectric relaxation for these interfacial polarizable molecules can be as large as 0.93 eV,i.e.89.73 kJ/mol.The present work provides a platform for characterizing the polymer-water electrostatic interactions and interfacial polarizable molecules,informative to understand the microstructure-property relationships of chitosan-based hydrogel materials.展开更多
Nowadays,thermal condition and solute field are considered as the potential dominant factors controlling competitive grain growth during directional solidification process.However,the controlling modes and critical co...Nowadays,thermal condition and solute field are considered as the potential dominant factors controlling competitive grain growth during directional solidification process.However,the controlling modes and critical conditions of competitive grain growth have been drastically debated over the past two decades.In this work,thermal condition and solute field are combined to study the competitive grain growth in the converging case by experimental observation and numerical simulation of bicrystal samples.We find the competitive grain growth is controlled by the cooperative effect of thermal condition and solute field,and the controlling modes are related to the bicrystal misorientation between favorably and unfavorably oriented grains.When the unfavorably oriented grain is low misoriented,unfavorably oriented grain dominates grain selection,and the competitive grain growth performs as solute field domination.However,with the increase of unfavorably oriented grain’s misorientation,the grain selection converts into favorably oriented grain domination,and the competitive grain growth changes to thermal condition domination.To explain these abnormal transformation phenomena,we propose a misorientation dependent thermal condition-solute field cooperative domination model and identify the critical conditions by a critical misorientation(θ_(cm)).According to dynamic equation of dendrite growth,we calculate the critical misorientationθ;to prove this model.The theoretical calculation results agree well with the experimental results.展开更多
Mn18Cr18N, the high-nitrogen steel, is the 2nd generation material for manufacturing the retaining ring of firepower generators. In this paper, the hot deformation behavior of the material was investigated by thermo-m...Mn18Cr18N, the high-nitrogen steel, is the 2nd generation material for manufacturing the retaining ring of firepower generators. In this paper, the hot deformation behavior of the material was investigated by thermo-mechanical modeling tests. And the flow stress curves of the steel were obtained for various combinations of the temperature and strain rate. Based on the results of the tests, the complex forming process of a retaining ring including punching, expanding and extrusion with an enclosure was put forward and simulated by means of numerical simulation method. The results indicate that the process is a novel and force-saved practical technology for manufacturing heavy retaining rings.展开更多
A novel TiO2-ZnFe2O4 coating is prepared by plasma spraying. The effects of spra ying parameters and the composition of powders on the microstructure, surface mo rphology and photo-absorption of plasma sprayed coating...A novel TiO2-ZnFe2O4 coating is prepared by plasma spraying. The effects of spra ying parameters and the composition of powders on the microstructure, surface mo rphology and photo-absorption of plasma sprayed coatings are studied. The photoc atalytic efficiency of the as-sprayed coatings is evaluated through the photo mi neralization of methylene blue. It was found that TiO2 coatings can decompose me thylene blue under the illumination of ultraviolet rays, and the degrading effic iency is improved with an increase in the content of FeTiO3 in the coatings. How ever, the presence of large amount of ZnFe2O4 compound will substantially lower the photocatalytic efficiency of the TiO2-ZnFe2O4 coatings for the unfavorable p hoto-excited electron-hole transfer process.展开更多
This paper reports the improvement of electrical,ferroelectric and endurance of Hf_(0.5)Zr_(0.5)O_(2)(HZO)thinfilm capacitors by implementing W electrode.The W/HZO/W capacitor shows excellent pristine 2 P_(r)values of...This paper reports the improvement of electrical,ferroelectric and endurance of Hf_(0.5)Zr_(0.5)O_(2)(HZO)thinfilm capacitors by implementing W electrode.The W/HZO/W capacitor shows excellent pristine 2 P_(r)values of 45.1 gC/cm^(2)at±6 V,which are much higher than those of TiN/HZO/W(34.4μC/cm^(2))and W/HZO/TiN(26.9μC/cm^(2))capacitors.Notably,the maximum initial 2 P_(r)value of W/HZO/W capacitor can reach as high as 57.9μC/cm^(2)at±7.5 V.These strong ferroelectric polarization effects are ascribed to the W electrode with a fairly low thermal expansion coefficient which provides a larger in-plane tensile strain compared with TiN electrode,allowing for enhancement of o-phase formation.Moreover,the W/HZO/W capacitor also exhibits higher endurance,smaller wake-up effect(10.1%)and superior fatigue properties up to 1.5×10^(10)cycles compared to the TiN/HZO/W and W/HZO/TiN capacitors.Such improvements of W/HZO/W capacitor are mainly due to the decreased leakage current by more than an order of magnitude compared to the W/HZO/TiN capacitor.These results demonstrate that capping electrode material plays an important role in the enhancement of o-phase formation,reduces oxygen vacancies,mitigates wake-up effect and improves reliability.展开更多
A universal numerical model based on the particle size distribution(PSD)approach has been developed for the simulation of precipitation kinetics in multicomponent alloys during isothermal ageing.Nucleation was impleme...A universal numerical model based on the particle size distribution(PSD)approach has been developed for the simulation of precipitation kinetics in multicomponent alloys during isothermal ageing.Nucleation was implemented utilizing the classical nucleation theory(CNT).Growth and coarsening were modeled by a single growth kinetics equation,which is constructed based on the interfacial diffusion flux balance and the capillarity effect.Only partial off-diagonal terms in the diffusion matrix(diffusion of individual components in the matrix)were taken into account in the calculations to minimize the computational cost while coupling with CALPHAD to extract thermodynamics equilibrium around the interface.A new feature of the model is the incorporation of a more realistic spatial site distribution via a Voronoi construction in the characteristic cell,for the purpose of modifying the diffusion distance.Computational predictions of the precipitate dimensions and the precipitation kinetics were compared with the atom probe tomography(APT)measurements on ternary Ni-Al-Cr alloys isothermally aged at 873 K.It is found that the temporal evolution of the dimensions and composition of the precipitates is well captured,as is the dependence on changes in the alloy composition.The new modification with Voronoi construction demonstrates that the overall precipitation kinetics depends on the density and the spatial site distribution of precipitates.The ability to handle sophisticated alloy chemistries by quantitative equations,the compositional sensitivity of microstructural characteristics emerging from the simulation results,and the ability to visualize the spatial distribution of precipitates make the work very promising for multicomponent alloy design and optimization.展开更多
The adaptive remeshing technique for quadrilateral elements consists of modules thetrigger of remeshing, the new mesh generation, adaptive refinement and interpolationof field variables. The new adaptive mesh genemtio...The adaptive remeshing technique for quadrilateral elements consists of modules thetrigger of remeshing, the new mesh generation, adaptive refinement and interpolationof field variables. The new adaptive mesh genemtion is the key problem. First, acoarse mesh is created by using 'loop algorithm'. Subsequent local mesh adaptiverefinement is performed based on effective strain. Finally, a typical example of upset-ting is given to test efficient of techniques, from which it is verified that the remeshingalgorithm developed here exhibits good performance and has high accuracy.展开更多
Porous Si3N4 was brazed to Invar alloy in this study, and Ag-Cu-Ti/Cu/Ag-Cu multi-layered filler was designed to inhibit the formation of Fe2Ti and Ni3Ti intermetallic compounds. The effects of the brazing temperature...Porous Si3N4 was brazed to Invar alloy in this study, and Ag-Cu-Ti/Cu/Ag-Cu multi-layered filler was designed to inhibit the formation of Fe2Ti and Ni3Ti intermetallic compounds. The effects of the brazing temperature and the thickness of Cu interlayer on the microstructure and mechanical properties of brazed joints were investigated. The typical microstructure of the joint brazed with multi-layered filler was porous Si3N4/TiN ＋ Ti5Si3/Ag-Cu eutectic[Cu[Ag-Cu eutectic/Cu-rich layer ＋ diffusion layer/Invar. When the brazing temperature increased, the reaction layer at the ceramic/filler interface grew thicker and the Cu interlayer turned thinner. As the thickness of Cu interlayer increased from 50 to 150 μm, the joint strength first increased and then decreased. In this research, the maximum shear strength （73 MPa） was obtained when being brazed at 1173 K with a 100 μm Cu interlayer applied in the filler, which was 55% higher than that brazed with single Ag-Cu-Ti brazing alloy and had reached 86% of the ceramic. The release of residual stress and the barrier effect of Cu interlayer to inhibit the formation of Fe2Ti and Ni3Ti intermetallics played the major role in the improvement of joint strength.展开更多
基金supported by the Natural Science Foundation of China(Grant Nos.11234005 and 51431006)the National 973 Projects of China(Grant No.2011CB922101).
文摘The RMn_(2)O_(5) manganite compounds represent one class of multiferroic family with magnetic origins,which has been receiving continuous attention in the past decade.So far,our understanding of the magnetic origins for ferroelectricity in RMn_(2)O_(5) is associated with the nearly collinear antiferromagnetic structure of Mn ions,while the exchange striction induced ionic displacements are the consequence of the spin frustration competitions.While this scenario may be applied to almost all RMn_(2)O_(5) members,its limitation is either clear:the temperature-dependent behaviors of electric polarization and its responses to external stimuli are seriously materials dependent.These inconsistences raise substantial concern with the state-of-the-art physics of ferroelectricity in RMn_(2)O_(5).In this mini-review,we present our recent experimental results on the roles of the 4f moments from R ions which are intimately coupled with the 3d moments from Mn ions.DyMn_(2)O_(5) is a golden figure for illustrating these roles.It is demonstrated that the spin structure accommodates two nearly collinear sublattices which generate respectively two ferroelectric(FE)sublattices,enabling DyMn_(2)O_(5) an emergent ferrielectric(FIE)system rarely identified in magnetically induced FEs.The evidence is presented from several aspects,including FIE-like phenomena and magnetoelectric responses,proposed structural model,and experimental check by nonmagnetic substitutions of the 3d and 4f moments.Additional perspectives regarding possible challenges in understanding the multiferroicity of RMn_(2)O_(5) as a generalized scenario are discussed.
基金supported by the National Natural Science Foundation of China(11102122)
文摘Using a stiffness matrix method, we in- vestigate the propagation behaviors of elastic waves in one-dimensional （1D） piezoelectric/piezomagnetic （PE/PM） phononic crystals （PCs） with line defects by calculating energy reflection/transmittion coefficients of quasi-pressure and quasi-shear waves. Line defects are created by the re- placement of PE or PM constituent layer. The defect modes existing in the first gap are considered and the influences on defect modes of the material properties and volume fraction of the defect layers, the type of incident waves, the location of defect layer and the number of structural layers are discussed in detail. Numerical results indicate that defect modes are the most obvious when the defect layers are inserted in the middle of the perfect PCs; the types of incidence wave and material properties of the defect layers have important effects on the numbers, the location of frequencies and the peaks of defect modes, and the defect modes are strongly de- pendent on volume fraction of the defect layers. We hope this paper will be found useful for the design of PE/PM acoustic filters or acoustic transducer with PCs structures.
基金This work was financially supported from the National Key Research Program of China(Grant Nos.2016YFA0300101 and 2015CB654602)the National Natural Science Foundation of China(Grant Nos.51431006 and 51721001).
文摘The functionalities of hydrogel-based smart materials are highly related to the electrostatic interactions and molecular polarization associated with the polymer networks and encapsulated water droplets,and therefore the dielectric responses of the polarizable molecules in the polymer,water,and polymer-water interfaces are particularly attractive,where the properties of polymer-water interfacial molecules remain elusive.Different from extensive dielectric relaxation spectroscopy studies on polymer hydrogel solutions,in this work we investigate the dielectric response of chitosan hydrogels below the water solidifying point(ice-hydrogels)so that the contribution of chitosan-water interfacial molecules can be isolated.It is revealed that the chitosan-water interfacial polarizable molecules have slow dielectric relaxation but large polarization compared with the chitosan chains and water molecules,and the dielectric relaxations beyond~10^(4)Hz are substantially weak.The thermal activation energy of the dielectric relaxation for these interfacial polarizable molecules can be as large as 0.93 eV,i.e.89.73 kJ/mol.The present work provides a platform for characterizing the polymer-water electrostatic interactions and interfacial polarizable molecules,informative to understand the microstructure-property relationships of chitosan-based hydrogel materials.
基金financially supported by the Shandong Provincial Natural Science Foundation(No.ZR2020ME110)the National Natural Science Foundation of China(Nos.51331005,U1508213,51771190 and 51601102)+2 种基金the Fund of the State Key Laboratory of Solidification Processing in NWPU(Nos.SKLSP201847 and SKLSP201834)the Young Doctors Cooperation Project in Qilu University of Technology(No.2018BSHZ003)the Key Research and Development Program of Ningxia(No.2019BDE03016)。
文摘Nowadays,thermal condition and solute field are considered as the potential dominant factors controlling competitive grain growth during directional solidification process.However,the controlling modes and critical conditions of competitive grain growth have been drastically debated over the past two decades.In this work,thermal condition and solute field are combined to study the competitive grain growth in the converging case by experimental observation and numerical simulation of bicrystal samples.We find the competitive grain growth is controlled by the cooperative effect of thermal condition and solute field,and the controlling modes are related to the bicrystal misorientation between favorably and unfavorably oriented grains.When the unfavorably oriented grain is low misoriented,unfavorably oriented grain dominates grain selection,and the competitive grain growth performs as solute field domination.However,with the increase of unfavorably oriented grain’s misorientation,the grain selection converts into favorably oriented grain domination,and the competitive grain growth changes to thermal condition domination.To explain these abnormal transformation phenomena,we propose a misorientation dependent thermal condition-solute field cooperative domination model and identify the critical conditions by a critical misorientation(θ_(cm)).According to dynamic equation of dendrite growth,we calculate the critical misorientationθ;to prove this model.The theoretical calculation results agree well with the experimental results.
文摘Mn18Cr18N, the high-nitrogen steel, is the 2nd generation material for manufacturing the retaining ring of firepower generators. In this paper, the hot deformation behavior of the material was investigated by thermo-mechanical modeling tests. And the flow stress curves of the steel were obtained for various combinations of the temperature and strain rate. Based on the results of the tests, the complex forming process of a retaining ring including punching, expanding and extrusion with an enclosure was put forward and simulated by means of numerical simulation method. The results indicate that the process is a novel and force-saved practical technology for manufacturing heavy retaining rings.
文摘A novel TiO2-ZnFe2O4 coating is prepared by plasma spraying. The effects of spra ying parameters and the composition of powders on the microstructure, surface mo rphology and photo-absorption of plasma sprayed coatings are studied. The photoc atalytic efficiency of the as-sprayed coatings is evaluated through the photo mi neralization of methylene blue. It was found that TiO2 coatings can decompose me thylene blue under the illumination of ultraviolet rays, and the degrading effic iency is improved with an increase in the content of FeTiO3 in the coatings. How ever, the presence of large amount of ZnFe2O4 compound will substantially lower the photocatalytic efficiency of the TiO2-ZnFe2O4 coatings for the unfavorable p hoto-excited electron-hole transfer process.
基金financially supported by the National Natural Science Foundation of China(No.51872099)the Hong Kong Research Grant Council(No.15300619)+2 种基金the Science and Technology Program of Guangzhou(No.201905-0001)the Guangdong Science and Technology Project-International Cooperation(No.2021A0505030064)financial support by the Hong Kong Scholars Program(No.XJ2019006)。
文摘This paper reports the improvement of electrical,ferroelectric and endurance of Hf_(0.5)Zr_(0.5)O_(2)(HZO)thinfilm capacitors by implementing W electrode.The W/HZO/W capacitor shows excellent pristine 2 P_(r)values of 45.1 gC/cm^(2)at±6 V,which are much higher than those of TiN/HZO/W(34.4μC/cm^(2))and W/HZO/TiN(26.9μC/cm^(2))capacitors.Notably,the maximum initial 2 P_(r)value of W/HZO/W capacitor can reach as high as 57.9μC/cm^(2)at±7.5 V.These strong ferroelectric polarization effects are ascribed to the W electrode with a fairly low thermal expansion coefficient which provides a larger in-plane tensile strain compared with TiN electrode,allowing for enhancement of o-phase formation.Moreover,the W/HZO/W capacitor also exhibits higher endurance,smaller wake-up effect(10.1%)and superior fatigue properties up to 1.5×10^(10)cycles compared to the TiN/HZO/W and W/HZO/TiN capacitors.Such improvements of W/HZO/W capacitor are mainly due to the decreased leakage current by more than an order of magnitude compared to the W/HZO/TiN capacitor.These results demonstrate that capping electrode material plays an important role in the enhancement of o-phase formation,reduces oxygen vacancies,mitigates wake-up effect and improves reliability.
基金financially supported by the National Natural Science Foundation of China(No.51871221)the National Key R&D Program of China(No.2020YFA0714900)the National Science and Technology Major Project(J2019-VI-0023-0139 and J2019-VII-0004-0144)。
文摘A universal numerical model based on the particle size distribution(PSD)approach has been developed for the simulation of precipitation kinetics in multicomponent alloys during isothermal ageing.Nucleation was implemented utilizing the classical nucleation theory(CNT).Growth and coarsening were modeled by a single growth kinetics equation,which is constructed based on the interfacial diffusion flux balance and the capillarity effect.Only partial off-diagonal terms in the diffusion matrix(diffusion of individual components in the matrix)were taken into account in the calculations to minimize the computational cost while coupling with CALPHAD to extract thermodynamics equilibrium around the interface.A new feature of the model is the incorporation of a more realistic spatial site distribution via a Voronoi construction in the characteristic cell,for the purpose of modifying the diffusion distance.Computational predictions of the precipitate dimensions and the precipitation kinetics were compared with the atom probe tomography(APT)measurements on ternary Ni-Al-Cr alloys isothermally aged at 873 K.It is found that the temporal evolution of the dimensions and composition of the precipitates is well captured,as is the dependence on changes in the alloy composition.The new modification with Voronoi construction demonstrates that the overall precipitation kinetics depends on the density and the spatial site distribution of precipitates.The ability to handle sophisticated alloy chemistries by quantitative equations,the compositional sensitivity of microstructural characteristics emerging from the simulation results,and the ability to visualize the spatial distribution of precipitates make the work very promising for multicomponent alloy design and optimization.
文摘The adaptive remeshing technique for quadrilateral elements consists of modules thetrigger of remeshing, the new mesh generation, adaptive refinement and interpolationof field variables. The new adaptive mesh genemtion is the key problem. First, acoarse mesh is created by using 'loop algorithm'. Subsequent local mesh adaptiverefinement is performed based on effective strain. Finally, a typical example of upset-ting is given to test efficient of techniques, from which it is verified that the remeshingalgorithm developed here exhibits good performance and has high accuracy.
基金supported by the National Nature Science Foundation of China (Grant Nos. 51372049, 51321061 and U1537206)
文摘Porous Si3N4 was brazed to Invar alloy in this study, and Ag-Cu-Ti/Cu/Ag-Cu multi-layered filler was designed to inhibit the formation of Fe2Ti and Ni3Ti intermetallic compounds. The effects of the brazing temperature and the thickness of Cu interlayer on the microstructure and mechanical properties of brazed joints were investigated. The typical microstructure of the joint brazed with multi-layered filler was porous Si3N4/TiN ＋ Ti5Si3/Ag-Cu eutectic[Cu[Ag-Cu eutectic/Cu-rich layer ＋ diffusion layer/Invar. When the brazing temperature increased, the reaction layer at the ceramic/filler interface grew thicker and the Cu interlayer turned thinner. As the thickness of Cu interlayer increased from 50 to 150 μm, the joint strength first increased and then decreased. In this research, the maximum shear strength （73 MPa） was obtained when being brazed at 1173 K with a 100 μm Cu interlayer applied in the filler, which was 55% higher than that brazed with single Ag-Cu-Ti brazing alloy and had reached 86% of the ceramic. The release of residual stress and the barrier effect of Cu interlayer to inhibit the formation of Fe2Ti and Ni3Ti intermetallics played the major role in the improvement of joint strength.
