A molecular dynamics simulation study was performed to investigate the formation and evolution mechanisms of nano-clusters during the rapid solidification of liquid CaToMg30 alloy. The cluster-type index method （CTIM...A molecular dynamics simulation study was performed to investigate the formation and evolution mechanisms of nano-clusters during the rapid solidification of liquid CaToMg30 alloy. The cluster-type index method （CTIM） was adopted to describe microstructure evolutions of nano-clusters during solidification. Results indicate that amorphous structure is mainly formed with three bond-types of 1551, 1541 and 1431 at the cooling rate of 5~1011 K/S, and glass transition temperature Tg is about 530 K; the icosahedron cluster of （12 0 12 0） plays a key role in formation of amorphous structure, and smaller Mg atoms are much more probable to be central atoms of icosahedron clusters; and nano-clusters are mainly formed by combining medium-size clusters. Interestingly, it was also found that formation and evolution processes of the nano-cluster display a three-stage feature which is analogous to crystallization process of amorphous alloy.展开更多
A novel Fe-Y composite oxide(Fe:Y-6.5) nanocluster was synthesized by self-assembly approach.The α-Fe_(2)O_(3) and cubic-Y_(2)O_(3) nanocrystalline with diameter around 10 nm are homogeneously assembled to form a clu...A novel Fe-Y composite oxide(Fe:Y-6.5) nanocluster was synthesized by self-assembly approach.The α-Fe_(2)O_(3) and cubic-Y_(2)O_(3) nanocrystalline with diameter around 10 nm are homogeneously assembled to form a cluster architecture which are constituted of Fe6.5Y composite oxide particles.Additional oxygen vacancies are introduced with cubic-Y_(2)O_(3),and the oxygen vacancies as Fe^(3+)-V_(0)-Y^(3+) between α-Fe_(2)O_(3) and cubic-Y_(2)O_(3) nanocrystalline are generated by self-assembly process.Magnetic hysteresis loops recorded by vibrating sample magnetometry at 273 K display a ferromagnetic order,related to the fact that Fe^(3+)-V_(o)-Y^(3+) act as defect centers in the bound magnetic polaron model for Fe-Y composite oxide nanomaterial.The ferromagnetic prope rties are proportional to oxygen vacancy co ntents,and maximum magnetization(M_(m)) value of the nano-cluster reaches 5.14 A·m^(2)/g.展开更多
Ni/Co bimetallic nano-cluters have been prepared from the aqueous solution byreducing their corresponding metal salts under suitable conditions. The experimental conditionsincluding the type and concentration of prote...Ni/Co bimetallic nano-cluters have been prepared from the aqueous solution byreducing their corresponding metal salts under suitable conditions. The experimental conditionsincluding the type and concentration of protective agent, feeding order and the pH of the solutionthat influence the average particle size have been studied in detail. Transmission electronmicroscopy (TEM) indicates that the shape of those bimetallic nano-cluster particles is spheroid.The alloy structure has been shown by X-ray powder diffraction (XRD). The X-ray photoelectronspectroscopic (XPS) data have confirmed that the nickel and cobalt in the bimetallic nano-clustersare in the zero-valence state.展开更多
First-principles energetics analyses were performed to investigate the nucleation of(Y-Si-O)nano-clusters(NCs)in nanostructured ferritic alloys(NFAs).It was predicted that the nucleation of(Y-Si-O)NCs follows the same...First-principles energetics analyses were performed to investigate the nucleation of(Y-Si-O)nano-clusters(NCs)in nanostructured ferritic alloys(NFAs).It was predicted that the nucleation of(Y-Si-O)NCs follows the same general pathway as previously found for(Y-Ti/Al/Zr-O)NCs in NFAs:they all tend to begin with the(O-O)pairs and grow to(O-Y)-cores and further to larger NCs by attracting Y and other solute elements nearby.Nucleation of a hexa-atomic-[2Y-Si-3O]-cluster can reduce the total energy by 4.71 eV.Among various microalloying-induced NCs,the nucleation preference ordering was predicted as(Y-Zr-O)>(Y-Ti-O)>(Y-Al-O)>(Y-Si-O).The number densities and chemical compositions of NCs in multi-microalloyed NFAs would largely depend on the number availability of(O,Y)-cores,as well as the relative abundance and atomic diffusivities of microalloying solute elements nearby.展开更多
In systems in atomic and nano scales such as clusters or agglomerates constituted of particles from a few to less than one hundred of atoms, quantum confinement effects are very important. Their optical and electronic...In systems in atomic and nano scales such as clusters or agglomerates constituted of particles from a few to less than one hundred of atoms, quantum confinement effects are very important. Their optical and electronic properties are often dependent on the size of the systems and the way in which the atoms in these clusters are bonded. Generally, these nano-structures display optical and electronic properties significantly different of those found in corresponding bulk materials. Silicon agglomerates found in Silicon Rich Oxide (SRO) films have optical properties, which have reported as depended directly on nano-crystal size. Furthermore, the room temperature photoluminescence (PL) of Silicon Rich Oxides (SRO) has repeatedly generated a huge interest due to their possible applications in optoelectronic devices. However, a plausible emission mechanism has not yet widespread acceptance of the scientific community. In this research, we employed the Density Functional Theory with a functional B3LYP and a basis set 6 - 31G* to calculate the optical and electronic properties of small (six to ten silicon atoms) and medium size clusters of silicon (constituted of eleven to fourteen silicon atoms). With the theoretical calculation of the structural and optical properties of silicon clusters, it is possible to evaluate the contribution of silicon agglomerates in the luminescent emission mechanism experimentally found in thin SRO films.展开更多
The development of high-performance metal nanocluster catalysts is hindered by a fundamental stabilization-activity trade-off.Oxide supports often induce over-stabilization via insulating overlayers that block active ...The development of high-performance metal nanocluster catalysts is hindered by a fundamental stabilization-activity trade-off.Oxide supports often induce over-stabilization via insulating overlayers that block active sites,while conventional functionalized carbon supports suffer from thermodynamic instability and weak metal-support electronic coupling,leading to aggregation.Herein,a novel defectmediated covalent anchoring strategy is presented to immobilize transition metal(Pd,Ru,and Ir)NCs within ordered mesoporous carbon.This approach leverages intrinsic micropore defects to capture precursors and facilitate in-situ formation of direct metal-carbon covalent bonds.Controlled pyrolysis confines metal atom sintering into clusters within the mesopores,achieving high metal loading.This enrooted architectu re uniquely balances stability and activity:it avoids the excessive metal-carbon bonding detrimental to single-atom catalysts while maintaining sufficient,controllable interactions.The resulting Pd NCs catalyst exhibits exceptional hydrogen oxidation reaction activity,surpassing mass activity benchmarks of conventional Pt/C.Critically,this methodology decouples atomic-scale stabilization from catalytic site accessibility,resolving the long-standing activity-stability dilemma and providing a generalizable platform for fabricating stable,high-loading cluster catalysts with optimized electronic structures.展开更多
基金Project(50831003) supported by the National Natural Science Foundation of ChinaProject(20114BAB215026) supported by Jiangxi Provincial Natural Science Foundation,ChinaProject(ZD201002) supported by Fund for Basic Scientific Research of Gannan Medical University,China
文摘A molecular dynamics simulation study was performed to investigate the formation and evolution mechanisms of nano-clusters during the rapid solidification of liquid CaToMg30 alloy. The cluster-type index method （CTIM） was adopted to describe microstructure evolutions of nano-clusters during solidification. Results indicate that amorphous structure is mainly formed with three bond-types of 1551, 1541 and 1431 at the cooling rate of 5~1011 K/S, and glass transition temperature Tg is about 530 K; the icosahedron cluster of （12 0 12 0） plays a key role in formation of amorphous structure, and smaller Mg atoms are much more probable to be central atoms of icosahedron clusters; and nano-clusters are mainly formed by combining medium-size clusters. Interestingly, it was also found that formation and evolution processes of the nano-cluster display a three-stage feature which is analogous to crystallization process of amorphous alloy.
基金Project supported by National Key R&D Program of China(2017YFB0305801)the Joint Funds of NSFC-Liaoning(U1508213)。
文摘A novel Fe-Y composite oxide(Fe:Y-6.5) nanocluster was synthesized by self-assembly approach.The α-Fe_(2)O_(3) and cubic-Y_(2)O_(3) nanocrystalline with diameter around 10 nm are homogeneously assembled to form a cluster architecture which are constituted of Fe6.5Y composite oxide particles.Additional oxygen vacancies are introduced with cubic-Y_(2)O_(3),and the oxygen vacancies as Fe^(3+)-V_(0)-Y^(3+) between α-Fe_(2)O_(3) and cubic-Y_(2)O_(3) nanocrystalline are generated by self-assembly process.Magnetic hysteresis loops recorded by vibrating sample magnetometry at 273 K display a ferromagnetic order,related to the fact that Fe^(3+)-V_(o)-Y^(3+) act as defect centers in the bound magnetic polaron model for Fe-Y composite oxide nanomaterial.The ferromagnetic prope rties are proportional to oxygen vacancy co ntents,and maximum magnetization(M_(m)) value of the nano-cluster reaches 5.14 A·m^(2)/g.
基金This work was supported in part by the project of KJCXGC-01 of Northwest Normal University the Joint Program between the Educational Committee and the Economic Trade Committee of Gansu Province, China (CX-04).]
文摘Ni/Co bimetallic nano-cluters have been prepared from the aqueous solution byreducing their corresponding metal salts under suitable conditions. The experimental conditionsincluding the type and concentration of protective agent, feeding order and the pH of the solutionthat influence the average particle size have been studied in detail. Transmission electronmicroscopy (TEM) indicates that the shape of those bimetallic nano-cluster particles is spheroid.The alloy structure has been shown by X-ray powder diffraction (XRD). The X-ray photoelectronspectroscopic (XPS) data have confirmed that the nickel and cobalt in the bimetallic nano-clustersare in the zero-valence state.
基金financially suppor ted by the National MCF Energy R&D Program of China(Project No.2018YFE0306100)the National Natural Science Foundation of China(No.51971249)。
文摘First-principles energetics analyses were performed to investigate the nucleation of(Y-Si-O)nano-clusters(NCs)in nanostructured ferritic alloys(NFAs).It was predicted that the nucleation of(Y-Si-O)NCs follows the same general pathway as previously found for(Y-Ti/Al/Zr-O)NCs in NFAs:they all tend to begin with the(O-O)pairs and grow to(O-Y)-cores and further to larger NCs by attracting Y and other solute elements nearby.Nucleation of a hexa-atomic-[2Y-Si-3O]-cluster can reduce the total energy by 4.71 eV.Among various microalloying-induced NCs,the nucleation preference ordering was predicted as(Y-Zr-O)>(Y-Ti-O)>(Y-Al-O)>(Y-Si-O).The number densities and chemical compositions of NCs in multi-microalloyed NFAs would largely depend on the number availability of(O,Y)-cores,as well as the relative abundance and atomic diffusivities of microalloying solute elements nearby.
文摘In systems in atomic and nano scales such as clusters or agglomerates constituted of particles from a few to less than one hundred of atoms, quantum confinement effects are very important. Their optical and electronic properties are often dependent on the size of the systems and the way in which the atoms in these clusters are bonded. Generally, these nano-structures display optical and electronic properties significantly different of those found in corresponding bulk materials. Silicon agglomerates found in Silicon Rich Oxide (SRO) films have optical properties, which have reported as depended directly on nano-crystal size. Furthermore, the room temperature photoluminescence (PL) of Silicon Rich Oxides (SRO) has repeatedly generated a huge interest due to their possible applications in optoelectronic devices. However, a plausible emission mechanism has not yet widespread acceptance of the scientific community. In this research, we employed the Density Functional Theory with a functional B3LYP and a basis set 6 - 31G* to calculate the optical and electronic properties of small (six to ten silicon atoms) and medium size clusters of silicon (constituted of eleven to fourteen silicon atoms). With the theoretical calculation of the structural and optical properties of silicon clusters, it is possible to evaluate the contribution of silicon agglomerates in the luminescent emission mechanism experimentally found in thin SRO films.
基金financially supported by the National Natural Science Foundation of China(No.U2030208&22279082)Sichuan Science and Technology Program(2025YFHZ0056)。
文摘The development of high-performance metal nanocluster catalysts is hindered by a fundamental stabilization-activity trade-off.Oxide supports often induce over-stabilization via insulating overlayers that block active sites,while conventional functionalized carbon supports suffer from thermodynamic instability and weak metal-support electronic coupling,leading to aggregation.Herein,a novel defectmediated covalent anchoring strategy is presented to immobilize transition metal(Pd,Ru,and Ir)NCs within ordered mesoporous carbon.This approach leverages intrinsic micropore defects to capture precursors and facilitate in-situ formation of direct metal-carbon covalent bonds.Controlled pyrolysis confines metal atom sintering into clusters within the mesopores,achieving high metal loading.This enrooted architectu re uniquely balances stability and activity:it avoids the excessive metal-carbon bonding detrimental to single-atom catalysts while maintaining sufficient,controllable interactions.The resulting Pd NCs catalyst exhibits exceptional hydrogen oxidation reaction activity,surpassing mass activity benchmarks of conventional Pt/C.Critically,this methodology decouples atomic-scale stabilization from catalytic site accessibility,resolving the long-standing activity-stability dilemma and providing a generalizable platform for fabricating stable,high-loading cluster catalysts with optimized electronic structures.
