This study shows that the mechanical strength of the composite of Fe matrix and titanium carbide(Ti C)ceramic particles is significantly enhanced with addition of molybdenum(Mo) atoms. Ti C reinforced Fe(Fe-0.2C-7Mn) ...This study shows that the mechanical strength of the composite of Fe matrix and titanium carbide(Ti C)ceramic particles is significantly enhanced with addition of molybdenum(Mo) atoms. Ti C reinforced Fe(Fe-0.2C-7Mn) composites with and without Mo were fabricated by a liquid pressing infiltration(LPI)process and the effect of Mo on interfacial properties of TiC–Fe composite was investigated using atomic probe tomography(APT) analysis, molecular dynamics(MD) simulations, first-principle density functional theory(DFT), and thermodynamic calculations. First, DFT calculations showed that total energies of the Mo-doped Ti C–Fe superlattices strongly depend on the position of Mo defects, and are minimized when the Mo atom is located at the TiC/Fe interface, supporting the probable formation of MoC-like interphase at the TiC/Fe interface region. Then, APT analysis confirmed the DFT predictions by finding that about6.5 wt.% Mo is incorporated in the Ti C–Fe(Mo) composite and that sub-micrometer thick(Ti,Mo)C interphase is indeed formed near the interface. The MD simulations show that Mo atoms migrate to the Mo-free TiC–Fe interface at elevated temperatures and the mechanical strength of the interface is considerably enhanced, which is in good agreement with experimental observations.展开更多
Atomic movement under application of external stimuli (i.e., electric field or mechanical stress) in oxide materials has not been observed due to a lack of experimental methods but has been well known to determine t...Atomic movement under application of external stimuli (i.e., electric field or mechanical stress) in oxide materials has not been observed due to a lack of experimental methods but has been well known to determine the electric polarization. Here, we investigated atomic movement arising from the ferroelectric response of BiFeO3 thin films under the effect of an electric field and stress in real time using a combination of switching spectroscop)6 time-resolved X-ray microdiffraction, and in situ stress engineering. Under an electric field applied to a BiFeO3 film, the hysteresis loop of the reflected X-ray intensity was found to result from the opposing directions of displaced atoms between the up and down polarization states. An additional shift of atoms arising from the linearly increased dielectric component of the polarization in BiFeO3 was confirmed through gradual reduction of the diffracted X-ray intensity. The electric-field- induced displacement of oxygen atoms was found to be larger than that of Fe atom for both ferroelectric switching and increase of the polarization. The effect of external stress on the BiFeO3 thin film, which was controlled by applying an electric field to the highly piezoelectric substrate, showed smaller atomic shifts than for the case of applying an electric field to the film, despite the similar tetragonality.展开更多
Physical property variation in dopant-free ZnO films was investigated. Film annealing under various environments(O_2, in-Air, N2 and vacuum) resulted in better crystallinity than in the as-grown film. In particular,...Physical property variation in dopant-free ZnO films was investigated. Film annealing under various environments(O_2, in-Air, N2 and vacuum) resulted in better crystallinity than in the as-grown film. In particular, the film annealed under the N_2 environment showed better crystallinity and electrical properties than films annealed in other environments. Based on spectroscopic analysis, we found a correlation between physical(structural, electrical) and chemical properties: The crystallinity of ZnO films is closely related to ZnO bonding, whereas carrier concentration is associated with VO(oxygen vacancy).展开更多
基金financially supported by the Fundamental Research Program (PNK7480) of the Korea Institute of Materials Science (KIMS)the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (NRF2020M3H4A3105943)+1 种基金supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF)funded by the Ministry of Education (NRF2014R1A1A2059123)。
文摘This study shows that the mechanical strength of the composite of Fe matrix and titanium carbide(Ti C)ceramic particles is significantly enhanced with addition of molybdenum(Mo) atoms. Ti C reinforced Fe(Fe-0.2C-7Mn) composites with and without Mo were fabricated by a liquid pressing infiltration(LPI)process and the effect of Mo on interfacial properties of TiC–Fe composite was investigated using atomic probe tomography(APT) analysis, molecular dynamics(MD) simulations, first-principle density functional theory(DFT), and thermodynamic calculations. First, DFT calculations showed that total energies of the Mo-doped Ti C–Fe superlattices strongly depend on the position of Mo defects, and are minimized when the Mo atom is located at the TiC/Fe interface, supporting the probable formation of MoC-like interphase at the TiC/Fe interface region. Then, APT analysis confirmed the DFT predictions by finding that about6.5 wt.% Mo is incorporated in the Ti C–Fe(Mo) composite and that sub-micrometer thick(Ti,Mo)C interphase is indeed formed near the interface. The MD simulations show that Mo atoms migrate to the Mo-free TiC–Fe interface at elevated temperatures and the mechanical strength of the interface is considerably enhanced, which is in good agreement with experimental observations.
文摘Atomic movement under application of external stimuli (i.e., electric field or mechanical stress) in oxide materials has not been observed due to a lack of experimental methods but has been well known to determine the electric polarization. Here, we investigated atomic movement arising from the ferroelectric response of BiFeO3 thin films under the effect of an electric field and stress in real time using a combination of switching spectroscop)6 time-resolved X-ray microdiffraction, and in situ stress engineering. Under an electric field applied to a BiFeO3 film, the hysteresis loop of the reflected X-ray intensity was found to result from the opposing directions of displaced atoms between the up and down polarization states. An additional shift of atoms arising from the linearly increased dielectric component of the polarization in BiFeO3 was confirmed through gradual reduction of the diffracted X-ray intensity. The electric-field- induced displacement of oxygen atoms was found to be larger than that of Fe atom for both ferroelectric switching and increase of the polarization. The effect of external stress on the BiFeO3 thin film, which was controlled by applying an electric field to the highly piezoelectric substrate, showed smaller atomic shifts than for the case of applying an electric field to the film, despite the similar tetragonality.
基金supported in part by NRF Korea (No. NRF2015R1D1A1A01058672)Korea Atomic Energy Research Institutesupported by the GPF Program (No. 2015H1A2A1034200) of NRF
文摘Physical property variation in dopant-free ZnO films was investigated. Film annealing under various environments(O_2, in-Air, N2 and vacuum) resulted in better crystallinity than in the as-grown film. In particular, the film annealed under the N_2 environment showed better crystallinity and electrical properties than films annealed in other environments. Based on spectroscopic analysis, we found a correlation between physical(structural, electrical) and chemical properties: The crystallinity of ZnO films is closely related to ZnO bonding, whereas carrier concentration is associated with VO(oxygen vacancy).