Iron-nitride films were prepared by reactive sputtering, and the effect of annealing treatment on the structures was investigated by means of in-situ electron microscopy and high resolution electron microscopy (HREM)....Iron-nitride films were prepared by reactive sputtering, and the effect of annealing treatment on the structures was investigated by means of in-situ electron microscopy and high resolution electron microscopy (HREM). As-deposited films were observed to be a mixed structure of a few ultrafine epsilon-Fe2-3N particles existing in the amorphous matrix. it was found that the structure-relaxation in the amorphous occurred at 473 K, and the ultrafine grains began to grow at the higher annealing temperatures. The transition of the amorphous to epsilon-Fe2-3N was almost completed at 673 K. It is considered that the formation of the ideal epsilon-Fe3N is originated from the ordering of the nitrogen atoms during the annealing in vacuum. On the other hand, gamma'-phase (Fe4N) was seen to precipitation of epsilon-phase at 723 K. Two possible modes are proposed in the precipitation of gamma'-phase, depending on the heating rate and crystallographic orientation relationships, i.e. [121](epsilon)//[001](gamma), (2(1) over bar0$)(epsilon)//(110)(gamma) and [100](epsilon)//[110](gamma), (001)(epsilon)//(111)(gamma). In addition, alpha-Fe particles were observed to form from the gamma'-phase at high temperatures. We assumed that these structural changes are due to the diffusion of nitrogen and iron atoms during the annealing, except for the case of the precipitation of the gamma'-phase as depicted above. The results obtained in this work are in a good agreement with the assumption.展开更多
Platinum-based fuel cell electrocatalysts are structured on a nano level in order to extend their active surface area and maximize the utilization of precious and scarce platinum.Their performance is dictated by the a...Platinum-based fuel cell electrocatalysts are structured on a nano level in order to extend their active surface area and maximize the utilization of precious and scarce platinum.Their performance is dictated by the atomic arrangement of their surface layers atoms via structure-property relationships.Transmission electron microscopy(TEM)and scanning transmission electron microscopy(STEM)are the preferred methods for characterizing these catalysts,due to their capacity to achieve local atomic-level resolutions.Size,morphology,strain and local composition are just some of the properties of Pt-based nanostructures that can be obtained by(S)TEM.Furthermore,advanced methods of(S)TEM are able to provide insights into the quasi-in situ,in situ or even operando stability of these nanostructures.In this review,we present state-of-the-art applications of(S)TEM in the investigation and interpretation of structure-activity and structure-stability relationships.展开更多
The forms and structures of the phases in Fe-Ni-Co-Nb-Ti-Si low expansion superal-loys have been studied using analytical electron microscopy, high resolution electron microscopy, chemical phase analysis, X-ray diffra...The forms and structures of the phases in Fe-Ni-Co-Nb-Ti-Si low expansion superal-loys have been studied using analytical electron microscopy, high resolution electron microscopy, chemical phase analysis, X-ray diffraction, etc. The effects of yttrium on the microstructures and properties in the superalloys have also been investigated. The results reveal that trace yttrium mainly located in the platelet precipitates makes the crystal structure changed. The platelet precipitates become smaller, denser and rather homogeneous with appropriate yttrium addition. Compared with the conventional low expansion superalloy, the misfit of the platelet phase with the matrix in the yttrium-containing low expansion superalloy decreases from 0.7% to 0.07%, which indicates very low stress at the interface.展开更多
The direct observations of the atomic arrangements in both conventional furnace annealed and electric pulse rapid annealed Fe78B13Si9 amorphous alloy have been conducted by the lattice imaging technique in a higt reso...The direct observations of the atomic arrangements in both conventional furnace annealed and electric pulse rapid annealed Fe78B13Si9 amorphous alloy have been conducted by the lattice imaging technique in a higt resolution electron microscope. The results showed that the embrittlement of the alloy was related to the extent of atomic rearrangements during the annealing processes. The embrittlement of the alloy after 1hour conventional furnace annealing at about 270℃ is caused by the sufficient atomic rearrangements which are characterized by the growth of some bct Fe3B-like atomic short range ordering regions already existed in the as-quenched structure. Electric pulse rapid annealing can effectively retard the above-mentioned atomic rearrangements and thus restrain the embrittlement. The embrittlement only occurs when certain amount of bcc α-Fe nanocrystals are precipitated in the amorphous matrix during electric pulse rapid annealing.展开更多
Strengthening due to precipitation of Cu in the a-Fe matrix is an important phenomenon utilized in the design of HSLA steels. In the present work, the microstructure of supersaturated solid solution in Fe-1.18%Cu bina...Strengthening due to precipitation of Cu in the a-Fe matrix is an important phenomenon utilized in the design of HSLA steels. In the present work, the microstructure of supersaturated solid solution in Fe-1.18%Cu binary alloy was investigated by means of high resolution electron microscopy. The results indicated that the solid solution was heterogeneous, there were lots of Cu atom clusters, which consisted of diffractive stripe microstructure similar to twin crystal. Orientation deviation was observed between two （110）o planes in diffractive stripes, which results in light and shade contrast. Furthermore, formation mechanisms of the nanometre stripe microstructure were discussed in terms of the interaction of Cu and Fe atoms in the Fe-Cu binary alloys.展开更多
ZnSe multipod-based structures,including tetrapod-like microrods,long microwires,and short nanorods,are selectively prepared by atmospheric pressure thermal evaporation of ZnSe nanoparticles without using any catalyst...ZnSe multipod-based structures,including tetrapod-like microrods,long microwires,and short nanorods,are selectively prepared by atmospheric pressure thermal evaporation of ZnSe nanoparticles without using any catalyst.The morphologies could be well controlled by simply adjusting the deposition position.The phase structures,morphologies,and optical properties of the products are investigated by X-ray diffraction(XRD),scanning electron microscopy(SEM),high-resolution transmission electron microscopy(TEM),and photoluminescence(PL) spectroscopy.A vapor-liquid mechanism is proposed for the formation of ZnSe multipod-based structures.The presented route is expected to be applied to the synthesis of other Ⅱ-Ⅵ groups or other group's semiconductor materials with controllable morphologies.展开更多
The microstructures and defects of various aged Sm( Co, Fe,Cu,Ti)_7 alloys have been observed in several orientations by using high resolution electron microscopy.Experimental results indicate that the alloy is compo...The microstructures and defects of various aged Sm( Co, Fe,Cu,Ti)_7 alloys have been observed in several orientations by using high resolution electron microscopy.Experimental results indicate that the alloy is composed of Sm2(Co,Fe,Cu,Ti)_(17)(2:17) phase with a small amount of titanium and Sm(Co,Fe,Cu)5,(1:5) phase.The 2:17 phase is rich in iron and the 1.5 phase is rich in copper.At aging stages corresponding to the peak magnetic coercivity,the alloy has a cellular-like microstructure with fine cells of the 2:17 phase surrounded by thin boundaries of the 1:5 phase.The average size of the cells is about 33 nm.The orientation relationship of [0001]_(2:17)/[0001]1:5 and(1210)_(2:17)/(0110)_(1:5) has been found in this alloy.The high resolution images show coherence between 2:17 phase and 1:5 phase and very small mismatch in some phase boundaries.The cells of 2:17 phase are full of microtwins with twin plane perpendicular to caxis.The cells of 2:17 phase rapidly grow up,when the aging temperature rises and aging time prolongs.For the alloy aged at 850℃, the 2:17 phase and 1:5 phase transform from cellular-like into striplike microstructure,and a few of twin boundaries can be seen in the 2:17 phase.Besides the twin boundaries,antiphase boundaries are sometimes observed in the 2:17 phase of the alloy aged at 800℃,for 10 h.展开更多
The characteristic of interface depending on the atomic structure exerts an inportant,and sometime controlling,influence on performance of the interacial materials. The present paper reviews the main studies on fine s...The characteristic of interface depending on the atomic structure exerts an inportant,and sometime controlling,influence on performance of the interacial materials. The present paper reviews the main studies on fine structure of both the materials inter- faces and interfacial reaction products in semiconductor uperlattice,metal multilayer ceram- ics and composite materials by mean of selected area electron doffraction patterns and high resolution electron microscopy. The following features of interfaces are reviewed:the orientation relationships;the char- acteristic of steps,facets and ronghness of interfaces;atomic bonding across the interface;the degree of coherency,the structure of misfit dislocations and elastic relaxations at the inter- faces:the presence of defects at the onterfaces:the structure of the interfacial reaction prod- ucts as well as the reaction kinetics and reaetion mechanism.展开更多
The microstructural characteristics of syntactic polycrystal in the calcium rare earth fluorocarbonate minerals from Southwest China have been studied by means of selected area electron diffraction and high resolutio...The microstructural characteristics of syntactic polycrystal in the calcium rare earth fluorocarbonate minerals from Southwest China have been studied by means of selected area electron diffraction and high resolution electron microscopy(HREM). The complication of the heterogeneous fabric of the minerals have been revealed by HREM. The results show that the crystal structure of the minerals was formed by a disorder stacking of the unit layers of bast naesite and synchisite in the calcium rare earth fluorocarbonate minerals along c direction. The stacking fault and other crystal defects in the syntactic polycrystal have been discussed.展开更多
The microstructures of the grain boundary phases in Fe-Ni-Co-Nb-Ti superalloy have been studied by high resolution electron microscopy (HREM).Besides the Laves phase,three other grain boundary phases have been found a...The microstructures of the grain boundary phases in Fe-Ni-Co-Nb-Ti superalloy have been studied by high resolution electron microscopy (HREM).Besides the Laves phase,three other grain boundary phases have been found and analyzed. The ε phase particles are needle-like with some stacking faults along the(0001) direction. The dominant phase at the grain boundaries is the orthorhombic phase that is also rod-like. High reselution image also confirms the existence of the triclinic phase at the grain boundaries that is irregular and scarce.展开更多
Li[Li0.2Ni0.13Coo.13Mn0.54]O2 cathode materials were synthesized by carbonate-based co-precipitation method, and then, its surface was coated by thin layers of FePO4. The prepared samples were characterized by X-ray d...Li[Li0.2Ni0.13Coo.13Mn0.54]O2 cathode materials were synthesized by carbonate-based co-precipitation method, and then, its surface was coated by thin layers of FePO4. The prepared samples were characterized by X-ray diffraction （XRD）, field emission scanning electron micro- scope （FESEM）, energy-dispersive spectroscopy （EDS）, and transmission electron microscopy （TEM）. The XRD and TEM results suggest that both the pristine and the coated materials have a hexagonal layered structure, and the FePO4 coating layer does not make any major change in the crystal structure. The FePO4-coated sample exhibits both improved initial discharge capacity and columbic efficiency compared to the pristine one. More significantly, the FePO4 coating layer has a much positive influence on the cycling perfor- mance. The FePO4-coated sample exhibits capacity reten- tion of 82 % after 100 cycles at 0.5℃ between 2.0 and 4.8 V, while only 28 % for the pristine one at the same charge-discharge condition. The electrochemical impe- dance spectroscopy （EIS） results indicate that this improved cycling performance could be ascribed to the presence of FePO4 on the surface of Li[Li0.2Ni0.13Co0.13Mno.54102 par- ticle, which helps to protect the cathode from chemical attacks by HF and thus suppresses the large increase in charge transfer resistance.展开更多
The evolutions of nano-twins and martensitic transformation in 316L austenitic stainless steel during large tensile deformation were studied by electron backscatter diffraction(EBSD)technology and transmission electro...The evolutions of nano-twins and martensitic transformation in 316L austenitic stainless steel during large tensile deformation were studied by electron backscatter diffraction(EBSD)technology and transmission electron microscopy(TEM)in detail.The results show that due to the low stacking fault energy of the steel,phase transformation induced plasticity(TRIP)and twinning induced plasticity(TWIP)coexist during the tensile deformation.The deformation firstly induces the formation of deformation twins,and dislocation pile-up is caused by the reduction of the dislocation mean free path(MFP)or grain refinement due to the twin boundaries,which further induces the martensitic transformation.With the increase of tensile deformation,a large number of nano-twins andα’-martensite appear,and the width of nano-twins decreases gradually,meanwhile the frequency of the intersecting deformation twins increases.The martensitic transformation can be divided into two types:γ-austenite→α’-martensite andγ-austenite→ε-martensite.α’-martensite is mainly distributed near the twin boundaries,especially at the intersection of twins,whileε-martensite and stacking faults exist in the form of transition products between the twins and the matrix.展开更多
The microstructural features of clacium rare earth(Ca RE) fluorocarbonate minerals from Southwest China were studied by using selected area electron diffraction(SAED) and high resolution transmission electron micros...The microstructural features of clacium rare earth(Ca RE) fluorocarbonate minerals from Southwest China were studied by using selected area electron diffraction(SAED) and high resolution transmission electron microscopy(HRTEM). Three new regularly mixed layer structures of B 8S 6 type with long period and different stacking sequence, i.e. B 8S 6 Ⅰ, B 8S 6 Ⅱ, and B 8S 6 Ⅲ, were found in the derived polycrystal of parisite, in which their structural symmetry, cell parameters, chemical formulas of crystal and stacking models of structural unit layer, etc. were determined. The results of this study also show that these new regularly mixed layer structrues were formed by order stacking unit layer of bastnaesite(B) and synchisite(S) in varying proportion along c axis. The observation under HRTEM reveals that in the three new regularly mixed layer structures there are different distribution modes of Ce F ion layers, CO 2- 3 ion groups between the Ce F ion layers, and CO 2- 3 ion groups between Ce F and Ca 2+ ion layers, and there are some heterogeneous textures, such as disorder interlayer and stacking fault. It further proves the complexity of the crystal structure of the Ca RE fluorocarbonate minerals.展开更多
In this study,we mainly focus on the structural morphology and inter-atomic bonding state of tribofilms resulting from a highly-hydrogenated amorphous carbon(a-C:H) film in order to ascertain the underlying mechanisms...In this study,we mainly focus on the structural morphology and inter-atomic bonding state of tribofilms resulting from a highly-hydrogenated amorphous carbon(a-C:H) film in order to ascertain the underlying mechanisms for its superlubric behavior(i.e.,less than 0.01 friction coefficient).Specifically,we achieved superlubricity(i.e.,friction coefficients of down to 0.003) with this film in dry nitrogen and argon atmospheres especially when the tribo-pair is made of an a-C:H coated Si disk sliding against an a-C:H coated steel ball,while the a-C:H coated disk against uncoated ball does not provide superlubricity.We also found that the state of superlubricity is more stable in argon than in nitrogen and the formation of a smooth and uniformly-thick carbonaceous tribofilm appears to be one of the key factors for the realization of such superlubricity.Besides,the interfacial morphology of sliding test pairs and the atomic-scale bond structure of the carbon-based tribofilms also play an important role in the observed superlubric behavior of a-C:H films.Using Raman spectroscopy and high resolution transmission electron microscopy,we have compared the structural differences of the tribofilms produced on bare and a-C:H coated steel balls.For the a-C:H coated ball as mating material which provided superlow friction in argon,structural morphology of the tribofilm was similar or comparable to that of the original a-C:H coating;while for the bare steel ball,the sp^2-bonded C fraction in the tribofilm increased and a fingerprint-like nanocrystalline structure was detected by high resolution transmission electron microscopy(HRTEM).We also calculated the shear stresses for different tribofilms,and established a relationship between the magnitude of the shear stresses and the extent of sp^3-sp^2 phase transformation.展开更多
Highly crystalline UO_(2)nanoparticles(NPs)with sizes of 2–3 nm were produced by fast chemical deposition of uranium(IV)under reducing conditions at pH 8–11.The particles were then characterized by microscopy and sp...Highly crystalline UO_(2)nanoparticles(NPs)with sizes of 2–3 nm were produced by fast chemical deposition of uranium(IV)under reducing conditions at pH 8–11.The particles were then characterized by microscopy and spectroscopy techniques including high-resolution transmission electron microscopy(HRTEM),X-ray diffraction(XRD),high-energy resolution fluorescence detection(HERFD)X-ray absorption spectroscopy at the U M_(4)edge and extended X-ray absorption fine structure(EXAFS)spectroscopy at the U L_(3)edge.The results of this investigation show that despite U(IV)being the dominant oxidation state of the freshly prepared UO_(2)NPs,they oxidize to U_(4)O_(9)with time and under the X-ray beam,indicating the high reactivity of U(IV)under these conditions.Moreover,it was found that the oxidation process of NPs is accompanied by their growth in size to 6 nm.We highlight here the major differences and similarities of the UO_(2)NP properties to PuO_(2),ThO_(2)and CeO_(2)NPs.展开更多
Lithium-rich layered oxide cathodes have an advantage of high energy density.However,continuous capacity fading and voltage hysteresis have largely restricted their practical application.In this work,we investigated i...Lithium-rich layered oxide cathodes have an advantage of high energy density.However,continuous capacity fading and voltage hysteresis have largely restricted their practical application.In this work,we investigated in depth the voltage-fading mechanism of Li-rich materials by in situ Raman spectroscopy,X-ray absorption near edge structure(XANES)spectroscopy,andhigh-resolution transmission electron microscopy(HRTEM).展开更多
Defects in crystalline structures play a vital role in their properties,so their proper characterization is essential to understanding and improving the behaviour of the materials.In this work,their presence in Ca_(4)...Defects in crystalline structures play a vital role in their properties,so their proper characterization is essential to understanding and improving the behaviour of the materials.In this work,their presence in Ca_(4)Fe_(9)O_(17) has been analysed.Its structure exhibits three different iron coordination topologies and can be described as layers of corner-sharing FeO_(5) bipyramids stacked along the c axis together with layers of edge-sharing FeO_(6) octahedra,both being linked by FeO_(4) tetrahedra.The relative position of the FeO_(4) tetrahedra generates three possible stacking directions,which results in stacking faults when more than one is combined.Structural refinement using the Rietveld method in X-ray and neutron powder diffraction data was not possible due to significant mismatches between the observed and calculated integrated intensities for several peaks resulting from this atomic disorder.Selected area electron diffraction(SAED)and high-resolution scanning transmission electron microscopy(HR-STEM)images confirm the local defective nature of the material.The FAULTS software enabled a successful refinement of the structure considering a high concentration of planar defects,conferred by the existence of three possible stacking directions in the crystal structure,all of them confined in the basal plane.展开更多
文摘Iron-nitride films were prepared by reactive sputtering, and the effect of annealing treatment on the structures was investigated by means of in-situ electron microscopy and high resolution electron microscopy (HREM). As-deposited films were observed to be a mixed structure of a few ultrafine epsilon-Fe2-3N particles existing in the amorphous matrix. it was found that the structure-relaxation in the amorphous occurred at 473 K, and the ultrafine grains began to grow at the higher annealing temperatures. The transition of the amorphous to epsilon-Fe2-3N was almost completed at 673 K. It is considered that the formation of the ideal epsilon-Fe3N is originated from the ordering of the nitrogen atoms during the annealing in vacuum. On the other hand, gamma'-phase (Fe4N) was seen to precipitation of epsilon-phase at 723 K. Two possible modes are proposed in the precipitation of gamma'-phase, depending on the heating rate and crystallographic orientation relationships, i.e. [121](epsilon)//[001](gamma), (2(1) over bar0$)(epsilon)//(110)(gamma) and [100](epsilon)//[110](gamma), (001)(epsilon)//(111)(gamma). In addition, alpha-Fe particles were observed to form from the gamma'-phase at high temperatures. We assumed that these structural changes are due to the diffusion of nitrogen and iron atoms during the annealing, except for the case of the precipitation of the gamma'-phase as depicted above. The results obtained in this work are in a good agreement with the assumption.
基金the Slovenian research agency(ARRS)programs P2-0393 and I0-0003the projects J2-3041,J7-4638,J7-4637 and N2-0257European Research Council(ERC)Starting Grant 123STABLE(Grant agreement ID:852208).
文摘Platinum-based fuel cell electrocatalysts are structured on a nano level in order to extend their active surface area and maximize the utilization of precious and scarce platinum.Their performance is dictated by the atomic arrangement of their surface layers atoms via structure-property relationships.Transmission electron microscopy(TEM)and scanning transmission electron microscopy(STEM)are the preferred methods for characterizing these catalysts,due to their capacity to achieve local atomic-level resolutions.Size,morphology,strain and local composition are just some of the properties of Pt-based nanostructures that can be obtained by(S)TEM.Furthermore,advanced methods of(S)TEM are able to provide insights into the quasi-in situ,in situ or even operando stability of these nanostructures.In this review,we present state-of-the-art applications of(S)TEM in the investigation and interpretation of structure-activity and structure-stability relationships.
基金sponsored by the National Basic Research Program of China(973 Program)under grant no.2015CB351905the National Natural Science Foundation of China(no.61504019)+3 种基金China Postdoctoral Science Foundation(no.2015M580783)Scientific Research Start-up Foundation of University of Electronic Science and Technology of China(Y02002010301082)the Technology Innovative Research Team of Sichuan Province of China(no.2015TD0005)the Fundamental Research Funds for the Central Universities of China(no.ZYGX2015J140)
基金Chinese foundation of aeronautical science( N o.96 G2 10 0 3)
文摘The forms and structures of the phases in Fe-Ni-Co-Nb-Ti-Si low expansion superal-loys have been studied using analytical electron microscopy, high resolution electron microscopy, chemical phase analysis, X-ray diffraction, etc. The effects of yttrium on the microstructures and properties in the superalloys have also been investigated. The results reveal that trace yttrium mainly located in the platelet precipitates makes the crystal structure changed. The platelet precipitates become smaller, denser and rather homogeneous with appropriate yttrium addition. Compared with the conventional low expansion superalloy, the misfit of the platelet phase with the matrix in the yttrium-containing low expansion superalloy decreases from 0.7% to 0.07%, which indicates very low stress at the interface.
文摘The direct observations of the atomic arrangements in both conventional furnace annealed and electric pulse rapid annealed Fe78B13Si9 amorphous alloy have been conducted by the lattice imaging technique in a higt resolution electron microscope. The results showed that the embrittlement of the alloy was related to the extent of atomic rearrangements during the annealing processes. The embrittlement of the alloy after 1hour conventional furnace annealing at about 270℃ is caused by the sufficient atomic rearrangements which are characterized by the growth of some bct Fe3B-like atomic short range ordering regions already existed in the as-quenched structure. Electric pulse rapid annealing can effectively retard the above-mentioned atomic rearrangements and thus restrain the embrittlement. The embrittlement only occurs when certain amount of bcc α-Fe nanocrystals are precipitated in the amorphous matrix during electric pulse rapid annealing.
基金Item Sponsored by National Natural Science Foundation of China (50361001)
文摘Strengthening due to precipitation of Cu in the a-Fe matrix is an important phenomenon utilized in the design of HSLA steels. In the present work, the microstructure of supersaturated solid solution in Fe-1.18%Cu binary alloy was investigated by means of high resolution electron microscopy. The results indicated that the solid solution was heterogeneous, there were lots of Cu atom clusters, which consisted of diffractive stripe microstructure similar to twin crystal. Orientation deviation was observed between two （110）o planes in diffractive stripes, which results in light and shade contrast. Furthermore, formation mechanisms of the nanometre stripe microstructure were discussed in terms of the interaction of Cu and Fe atoms in the Fe-Cu binary alloys.
文摘ZnSe multipod-based structures,including tetrapod-like microrods,long microwires,and short nanorods,are selectively prepared by atmospheric pressure thermal evaporation of ZnSe nanoparticles without using any catalyst.The morphologies could be well controlled by simply adjusting the deposition position.The phase structures,morphologies,and optical properties of the products are investigated by X-ray diffraction(XRD),scanning electron microscopy(SEM),high-resolution transmission electron microscopy(TEM),and photoluminescence(PL) spectroscopy.A vapor-liquid mechanism is proposed for the formation of ZnSe multipod-based structures.The presented route is expected to be applied to the synthesis of other Ⅱ-Ⅵ groups or other group's semiconductor materials with controllable morphologies.
文摘The microstructures and defects of various aged Sm( Co, Fe,Cu,Ti)_7 alloys have been observed in several orientations by using high resolution electron microscopy.Experimental results indicate that the alloy is composed of Sm2(Co,Fe,Cu,Ti)_(17)(2:17) phase with a small amount of titanium and Sm(Co,Fe,Cu)5,(1:5) phase.The 2:17 phase is rich in iron and the 1.5 phase is rich in copper.At aging stages corresponding to the peak magnetic coercivity,the alloy has a cellular-like microstructure with fine cells of the 2:17 phase surrounded by thin boundaries of the 1:5 phase.The average size of the cells is about 33 nm.The orientation relationship of [0001]_(2:17)/[0001]1:5 and(1210)_(2:17)/(0110)_(1:5) has been found in this alloy.The high resolution images show coherence between 2:17 phase and 1:5 phase and very small mismatch in some phase boundaries.The cells of 2:17 phase are full of microtwins with twin plane perpendicular to caxis.The cells of 2:17 phase rapidly grow up,when the aging temperature rises and aging time prolongs.For the alloy aged at 850℃, the 2:17 phase and 1:5 phase transform from cellular-like into striplike microstructure,and a few of twin boundaries can be seen in the 2:17 phase.Besides the twin boundaries,antiphase boundaries are sometimes observed in the 2:17 phase of the alloy aged at 800℃,for 10 h.
文摘The characteristic of interface depending on the atomic structure exerts an inportant,and sometime controlling,influence on performance of the interacial materials. The present paper reviews the main studies on fine structure of both the materials inter- faces and interfacial reaction products in semiconductor uperlattice,metal multilayer ceram- ics and composite materials by mean of selected area electron doffraction patterns and high resolution electron microscopy. The following features of interfaces are reviewed:the orientation relationships;the char- acteristic of steps,facets and ronghness of interfaces;atomic bonding across the interface;the degree of coherency,the structure of misfit dislocations and elastic relaxations at the inter- faces:the presence of defects at the onterfaces:the structure of the interfacial reaction prod- ucts as well as the reaction kinetics and reaetion mechanism.
文摘The microstructural characteristics of syntactic polycrystal in the calcium rare earth fluorocarbonate minerals from Southwest China have been studied by means of selected area electron diffraction and high resolution electron microscopy(HREM). The complication of the heterogeneous fabric of the minerals have been revealed by HREM. The results show that the crystal structure of the minerals was formed by a disorder stacking of the unit layers of bast naesite and synchisite in the calcium rare earth fluorocarbonate minerals along c direction. The stacking fault and other crystal defects in the syntactic polycrystal have been discussed.
文摘The microstructures of the grain boundary phases in Fe-Ni-Co-Nb-Ti superalloy have been studied by high resolution electron microscopy (HREM).Besides the Laves phase,three other grain boundary phases have been found and analyzed. The ε phase particles are needle-like with some stacking faults along the(0001) direction. The dominant phase at the grain boundaries is the orthorhombic phase that is also rod-like. High reselution image also confirms the existence of the triclinic phase at the grain boundaries that is irregular and scarce.
基金financially supported by the National Natural Science Foundation of China(No.51365014)the Industrial Support Key Project of Jiangxi Province,China(No.20161BBE50072)
基金financially supported by the National Nature Science Foundation of China (No.51302017)the National High Technology Research and Development Program of China (No.2012AA110102)the fund from the Science and Technology Commission of Beijing (No.2121100006712002)
文摘Li[Li0.2Ni0.13Coo.13Mn0.54]O2 cathode materials were synthesized by carbonate-based co-precipitation method, and then, its surface was coated by thin layers of FePO4. The prepared samples were characterized by X-ray diffraction （XRD）, field emission scanning electron micro- scope （FESEM）, energy-dispersive spectroscopy （EDS）, and transmission electron microscopy （TEM）. The XRD and TEM results suggest that both the pristine and the coated materials have a hexagonal layered structure, and the FePO4 coating layer does not make any major change in the crystal structure. The FePO4-coated sample exhibits both improved initial discharge capacity and columbic efficiency compared to the pristine one. More significantly, the FePO4 coating layer has a much positive influence on the cycling perfor- mance. The FePO4-coated sample exhibits capacity reten- tion of 82 % after 100 cycles at 0.5℃ between 2.0 and 4.8 V, while only 28 % for the pristine one at the same charge-discharge condition. The electrochemical impe- dance spectroscopy （EIS） results indicate that this improved cycling performance could be ascribed to the presence of FePO4 on the surface of Li[Li0.2Ni0.13Co0.13Mno.54102 par- ticle, which helps to protect the cathode from chemical attacks by HF and thus suppresses the large increase in charge transfer resistance.
基金supported by the Natural Science Foundation of Shaanxi Province,China(No.2021JM-061).
文摘The evolutions of nano-twins and martensitic transformation in 316L austenitic stainless steel during large tensile deformation were studied by electron backscatter diffraction(EBSD)technology and transmission electron microscopy(TEM)in detail.The results show that due to the low stacking fault energy of the steel,phase transformation induced plasticity(TRIP)and twinning induced plasticity(TWIP)coexist during the tensile deformation.The deformation firstly induces the formation of deformation twins,and dislocation pile-up is caused by the reduction of the dislocation mean free path(MFP)or grain refinement due to the twin boundaries,which further induces the martensitic transformation.With the increase of tensile deformation,a large number of nano-twins andα’-martensite appear,and the width of nano-twins decreases gradually,meanwhile the frequency of the intersecting deformation twins increases.The martensitic transformation can be divided into two types:γ-austenite→α’-martensite andγ-austenite→ε-martensite.α’-martensite is mainly distributed near the twin boundaries,especially at the intersection of twins,whileε-martensite and stacking faults exist in the form of transition products between the twins and the matrix.
文摘The microstructural features of clacium rare earth(Ca RE) fluorocarbonate minerals from Southwest China were studied by using selected area electron diffraction(SAED) and high resolution transmission electron microscopy(HRTEM). Three new regularly mixed layer structures of B 8S 6 type with long period and different stacking sequence, i.e. B 8S 6 Ⅰ, B 8S 6 Ⅱ, and B 8S 6 Ⅲ, were found in the derived polycrystal of parisite, in which their structural symmetry, cell parameters, chemical formulas of crystal and stacking models of structural unit layer, etc. were determined. The results of this study also show that these new regularly mixed layer structrues were formed by order stacking unit layer of bastnaesite(B) and synchisite(S) in varying proportion along c axis. The observation under HRTEM reveals that in the three new regularly mixed layer structures there are different distribution modes of Ce F ion layers, CO 2- 3 ion groups between the Ce F ion layers, and CO 2- 3 ion groups between Ce F and Ca 2+ ion layers, and there are some heterogeneous textures, such as disorder interlayer and stacking fault. It further proves the complexity of the crystal structure of the Ca RE fluorocarbonate minerals.
基金supported by the National Basic Research Program of China (Grant No.2011CB013404)National Natural Science Foundation of China(Grant Nos.51321092,51527901 and 51375010)
文摘In this study,we mainly focus on the structural morphology and inter-atomic bonding state of tribofilms resulting from a highly-hydrogenated amorphous carbon(a-C:H) film in order to ascertain the underlying mechanisms for its superlubric behavior(i.e.,less than 0.01 friction coefficient).Specifically,we achieved superlubricity(i.e.,friction coefficients of down to 0.003) with this film in dry nitrogen and argon atmospheres especially when the tribo-pair is made of an a-C:H coated Si disk sliding against an a-C:H coated steel ball,while the a-C:H coated disk against uncoated ball does not provide superlubricity.We also found that the state of superlubricity is more stable in argon than in nitrogen and the formation of a smooth and uniformly-thick carbonaceous tribofilm appears to be one of the key factors for the realization of such superlubricity.Besides,the interfacial morphology of sliding test pairs and the atomic-scale bond structure of the carbon-based tribofilms also play an important role in the observed superlubric behavior of a-C:H films.Using Raman spectroscopy and high resolution transmission electron microscopy,we have compared the structural differences of the tribofilms produced on bare and a-C:H coated steel balls.For the a-C:H coated ball as mating material which provided superlow friction in argon,structural morphology of the tribofilm was similar or comparable to that of the original a-C:H coating;while for the bare steel ball,the sp^2-bonded C fraction in the tribofilm increased and a fingerprint-like nanocrystalline structure was detected by high resolution transmission electron microscopy(HRTEM).We also calculated the shear stresses for different tribofilms,and established a relationship between the magnitude of the shear stresses and the extent of sp^3-sp^2 phase transformation.
基金funded by the European Commission Council under ERC[grant no.759696]support from RFBR(projectnumber no.19-33-90127)+1 种基金support by the Russian Ministry of Science and Education under grant no.075-15-2019-1891support from the Swedish Research Council(grant 2017-06465).
文摘Highly crystalline UO_(2)nanoparticles(NPs)with sizes of 2–3 nm were produced by fast chemical deposition of uranium(IV)under reducing conditions at pH 8–11.The particles were then characterized by microscopy and spectroscopy techniques including high-resolution transmission electron microscopy(HRTEM),X-ray diffraction(XRD),high-energy resolution fluorescence detection(HERFD)X-ray absorption spectroscopy at the U M_(4)edge and extended X-ray absorption fine structure(EXAFS)spectroscopy at the U L_(3)edge.The results of this investigation show that despite U(IV)being the dominant oxidation state of the freshly prepared UO_(2)NPs,they oxidize to U_(4)O_(9)with time and under the X-ray beam,indicating the high reactivity of U(IV)under these conditions.Moreover,it was found that the oxidation process of NPs is accompanied by their growth in size to 6 nm.We highlight here the major differences and similarities of the UO_(2)NP properties to PuO_(2),ThO_(2)and CeO_(2)NPs.
基金financially supported by the Basic Research Project of the Science and Technology Innovation Commission of Shenzhen(no.JCYJ20170412153139454)the National Natural Science Foundation of China(no.21875097)+1 种基金Natural Science Foundation of Guangdong Province(no.2018A030313725 and 2018B030322001)the Professorial and Doctoral Scientific Research Foundation of Huizhou University(no.2020JB025).
文摘Lithium-rich layered oxide cathodes have an advantage of high energy density.However,continuous capacity fading and voltage hysteresis have largely restricted their practical application.In this work,we investigated in depth the voltage-fading mechanism of Li-rich materials by in situ Raman spectroscopy,X-ray absorption near edge structure(XANES)spectroscopy,andhigh-resolution transmission electron microscopy(HRTEM).
基金ALBA synchrotron(proposal 2019073634)ILL(EASY access system)+1 种基金Spain’s Agencia Estatal de Investigación Severo Ochoa Program for Centers of Excellence in R&D(CEX2019-000917-S)funding through grant PID2020-113805GB-I00.
文摘Defects in crystalline structures play a vital role in their properties,so their proper characterization is essential to understanding and improving the behaviour of the materials.In this work,their presence in Ca_(4)Fe_(9)O_(17) has been analysed.Its structure exhibits three different iron coordination topologies and can be described as layers of corner-sharing FeO_(5) bipyramids stacked along the c axis together with layers of edge-sharing FeO_(6) octahedra,both being linked by FeO_(4) tetrahedra.The relative position of the FeO_(4) tetrahedra generates three possible stacking directions,which results in stacking faults when more than one is combined.Structural refinement using the Rietveld method in X-ray and neutron powder diffraction data was not possible due to significant mismatches between the observed and calculated integrated intensities for several peaks resulting from this atomic disorder.Selected area electron diffraction(SAED)and high-resolution scanning transmission electron microscopy(HR-STEM)images confirm the local defective nature of the material.The FAULTS software enabled a successful refinement of the structure considering a high concentration of planar defects,conferred by the existence of three possible stacking directions in the crystal structure,all of them confined in the basal plane.
