The inversion degree(X)of a spinel-type nanomaterial is an essential parameter to understand the mag netic and electronic properties of ferrites.In this work,we have related different theoretical and experi mental app...The inversion degree(X)of a spinel-type nanomaterial is an essential parameter to understand the mag netic and electronic properties of ferrites.In this work,we have related different theoretical and experi mental approaches in order to know the X parameter of a Co-based spinel.Our hypothesis is that the hys teresis curve at 5 K may be used tofind the X parameter taking into consideration that the coercivity and remanence of this kind of nanoparticle(NP)are strongly dependent on the cation distribution between A and B sites of the spinel structure.To investigate this,CoFe_(2)O_(4)NPs werefirstly synthesized and fully characterized by powder X-ray diffraction(PXRD),transmission electron microscopy(TEM),and vibrating sample magnetometry(VSM).These results pointed out monodisperse CoFe_(2)O_(4)nanostructures with a spherical shape of 6.85±0.05 nm.Subsequently,first-principles calculations were carried out to obtain the most stable atomic configuration as a function of the level of inversion,as well as the atomic pro perties for each X.Then,these data were used to define the constants used in the micromagnetic calcu lations.A hysteresis loop was generated for each X and further compared to the experimental curve measured at 5 K.In this sense,the bestfit was found for X=0.75,which indicates this value as the most probable inversion degree for the CoFe_(2)O_(4)nanostructures investigated in this work.Overall,we are able to connect the experiments with the atomistic explanation through micromagnetic simulations in order tofind the cationic configuration of the Co-based spinel nanostructure.展开更多
Noble-metal-based catalysts are the most used nanomaterials to carry out electrochemical reactions,which are commonly applied in fuel cells.This kind of catalyst is expensive and it is worth mentioning that noble meta...Noble-metal-based catalysts are the most used nanomaterials to carry out electrochemical reactions,which are commonly applied in fuel cells.This kind of catalyst is expensive and it is worth mentioning that noble metals are scarce.So,nanocatalysts based on cheaper metals,such as Ag and Cu,are highly desired.Here,we report the natural arrangement of different Ag_(x)Cu_(y)nanostructures through oleylamine reduction.Firstly,an experimental study was carried out in order to study the crystallographic structure,size,and shape of each synthesized nanostructure.The samples were fully characterized via powder X-ray diffraction,while scanning-transmission electron microscopy with a high-angle annular dark-field(HAADF)was applied to investigate the morphological features.Interestingly,the HAADF images of the AgCu NPs mostly show a Janus-type configuration,instead of a core-shell architecture,which is the most stable atomic arrangement.Given this,we subsequently performed classical molecular dynamics simulations under the NVT canonical ensemble to further deepen our study.The theoretical results pointed out that the nanostructure with a core-shell morphology is the one with the lowest energy.However,it also indicates an energy decrease in the Janus configuration,as long as the NP size increases.Therefore,for nanostructures with a large number of atoms,this could lead to a strong competition between Janus and core-shell arrangement.Finally,considering the AgCu NP size,it is worth noting that the theoretical data supports the experimental results,making these systems interesting not only because of their properties but also due to the relatively easy synthesis procedure.展开更多
基金support of ICM P10-061-F by Fondo de Innovación para la Competitividad-Minecon,the Basal Funding for Scientific and Technological Centers number AFB180001 CEDENNA(Conicyt)Fondecyt Projects numbers 3170240,11170544,1200782 and 1201491+2 种基金JLP acknowledges CIP2018006 from Universidad Central de ChileSEB acknowledges the support of DICYT project 041931BRthe super computing infrastructure of the NLHPC(ECM-02).
文摘The inversion degree(X)of a spinel-type nanomaterial is an essential parameter to understand the mag netic and electronic properties of ferrites.In this work,we have related different theoretical and experi mental approaches in order to know the X parameter of a Co-based spinel.Our hypothesis is that the hys teresis curve at 5 K may be used tofind the X parameter taking into consideration that the coercivity and remanence of this kind of nanoparticle(NP)are strongly dependent on the cation distribution between A and B sites of the spinel structure.To investigate this,CoFe_(2)O_(4)NPs werefirstly synthesized and fully characterized by powder X-ray diffraction(PXRD),transmission electron microscopy(TEM),and vibrating sample magnetometry(VSM).These results pointed out monodisperse CoFe_(2)O_(4)nanostructures with a spherical shape of 6.85±0.05 nm.Subsequently,first-principles calculations were carried out to obtain the most stable atomic configuration as a function of the level of inversion,as well as the atomic pro perties for each X.Then,these data were used to define the constants used in the micromagnetic calcu lations.A hysteresis loop was generated for each X and further compared to the experimental curve measured at 5 K.In this sense,the bestfit was found for X=0.75,which indicates this value as the most probable inversion degree for the CoFe_(2)O_(4)nanostructures investigated in this work.Overall,we are able to connect the experiments with the atomistic explanation through micromagnetic simulations in order tofind the cationic configuration of the Co-based spinel nanostructure.
基金FONDECYT(grants 3170240 and 1200782)Basal Program for Centers of Excellence,Grant AFB180001 CEDENNA,CONICYT+1 种基金DICYT project 041931BRUSA1799 Vridei 041931SB_GO。
文摘Noble-metal-based catalysts are the most used nanomaterials to carry out electrochemical reactions,which are commonly applied in fuel cells.This kind of catalyst is expensive and it is worth mentioning that noble metals are scarce.So,nanocatalysts based on cheaper metals,such as Ag and Cu,are highly desired.Here,we report the natural arrangement of different Ag_(x)Cu_(y)nanostructures through oleylamine reduction.Firstly,an experimental study was carried out in order to study the crystallographic structure,size,and shape of each synthesized nanostructure.The samples were fully characterized via powder X-ray diffraction,while scanning-transmission electron microscopy with a high-angle annular dark-field(HAADF)was applied to investigate the morphological features.Interestingly,the HAADF images of the AgCu NPs mostly show a Janus-type configuration,instead of a core-shell architecture,which is the most stable atomic arrangement.Given this,we subsequently performed classical molecular dynamics simulations under the NVT canonical ensemble to further deepen our study.The theoretical results pointed out that the nanostructure with a core-shell morphology is the one with the lowest energy.However,it also indicates an energy decrease in the Janus configuration,as long as the NP size increases.Therefore,for nanostructures with a large number of atoms,this could lead to a strong competition between Janus and core-shell arrangement.Finally,considering the AgCu NP size,it is worth noting that the theoretical data supports the experimental results,making these systems interesting not only because of their properties but also due to the relatively easy synthesis procedure.
