The mechanical behavior of a magnesium alloy E-form under bending was investigated using the elasto-visco-plastic polycrystal model(ΔEVPSC) and its finite element(FE) implementation(ΔEVPSC-FE) developed in Jeong et ...The mechanical behavior of a magnesium alloy E-form under bending was investigated using the elasto-visco-plastic polycrystal model(ΔEVPSC) and its finite element(FE) implementation(ΔEVPSC-FE) developed in Jeong et al. and Jeong and Tomé. The crystallographic orientation distribution(COD) obtained from X-ray diffraction was used to represent the initial texture, and the Voce hardening parameters were calibrated by fitting the uniaxial tension and the compression flow stress curves. A quasi-static FE analysis of a miniaturized V-bending operation was conducted using the ΔEVPSC-FE model. The bending induced an inhomogeneous stress response along the through-thickness and the lateral directions, which was well captured by the model. Moreover, the predictive capability of the model was validated by comparing with various experimental results such as(1) force vs. displacement curves;(2) the through-thickness variations in the twin volume fraction;and(3) the changes in crystallographic texture as a function of displacement. Additional bending simulation was performed using an isotropic texture, the result of which suggests that the potential improvement in bendability of the magnesium alloy is attainable by weakening the initial texture. Moreover, the simulation results imply that the crystallographic texture, which may affect the twin activation across the thickness direction, plays a significant role in the shifting direction of the neutral layer.展开更多
PrBa_(0.5)Sr_(0.5)Co_(1.5)Fe_(0.5)O_(5+δ)(PrBSCF) has attracted much research interest as a potential triple ionic and electronic conductor(TIEC) electrode for protonic ceramic fuel cells(PCFCs). The chemical formula...PrBa_(0.5)Sr_(0.5)Co_(1.5)Fe_(0.5)O_(5+δ)(PrBSCF) has attracted much research interest as a potential triple ionic and electronic conductor(TIEC) electrode for protonic ceramic fuel cells(PCFCs). The chemical formula for Pr BSCF is AA'B_(2)O_(5+δ), with Pr(A-site) and Ba/Sr(A'-site) alternately stacked along the c-axis. Due to these structural features, the bulk oxygen ion diffusivity is significantly enhanced through the disorder-free channels in the PrO layer;thus, the A site cations(lanthanide ions) play a pivotal role in determining the overall electrochemical properties of layered perovskites. Consequently, previous research has predominantly focused on the electrical properties and oxygen bulk/surface kinetics of Ln cation effects,whereas the hydration properties for PCFC systems remain unidentified. Here, we thoroughly examined the proton uptake behavior and thermodynamic parameters for the hydration reaction to conclusively determine the changes in the electrochemical performances depending on LnBa_(0.5)Sr_(0.5)Co_(1.5)Fe_(0.5)O_(5+δ)(LnBSCF,Ln=Pr, Nd, and Gd) cathodes. At 500 ℃, the quantitative proton concentration of PrBSCF was 2.04 mol% and progressively decreased as the Ln cation size decreased. Similarly, the Gibbs free energy indicated that less energy was required for the formation of protonic defects in the order of Pr BSCF < Nd BSCF < Gd BSCF. To elucidate the close relationship between hydration properties and electrochemical performances in LnBSCF cathodes, PCFC single cell measurements and analysis of the distribution of relaxation time were further investigated.展开更多
Absorption and desorption processes of hydrogen in metals are facilitated by alloying elements;however,the formation of secondary phases often reduces storage capacity.The alloying effect on the hydrogen kinetics has ...Absorption and desorption processes of hydrogen in metals are facilitated by alloying elements;however,the formation of secondary phases often reduces storage capacity.The alloying effect on the hydrogen kinetics has been examined by time-lag permeation measurement,which lacks spatial resolution and yields the averaged diffusion coefficient from multiple phases.Here,we report an advanced scanning Kelvin probe force microscopy,combined with in-situ hydrogen loading system for submicron-scale measurement of diffusion kinetics in metals.Successive probing of the surface during hydrogen loading detects the temporal and spatial variations in the surface potential,enabling the estimation of diffusion coefficient.Not only for a single-phase magnesium but also for multiphase titaniumiron based alloys,we can obtain the diffusion coefficients of hydrogen in each phase.The estimated diffusion coefficients for TiFe alloys are higher than that for the pristine TiFe intermetallic compound,due to alloying elements that reduce the diffusion barrier and modify bond character.Our approach paves the way to the microscopic understanding of hydrogen diffusion in metals.展开更多
The atomically thin nature of two-dimensional(2D)layered materials makes them susceptible to charge trapping by randomly created disorders,adversely affecting carrier dynamics such as charge transport and exciton life...The atomically thin nature of two-dimensional(2D)layered materials makes them susceptible to charge trapping by randomly created disorders,adversely affecting carrier dynamics such as charge transport and exciton lifetime.Typically,these disorders lead to poor device performance or require additional space to mitigate performance degradation.In this study,we investigate 2D layered Dion–Jacobson(DJ)-phase oxide perovskite nanosheets,which exhibit charge trapping within their well-defined quantum well(QW)structures,resulting in unique tailoring of electrical conductivity and photoconductivity.These DJ-phase perovskites,composed of tunable atomic constituents,demonstrate resonant tunneling and anomalous charge trapping due to their ultra-clean QWs.Remarkably,the conductivity of insulating HSr_(2)Nb_(3)O_(10)(HSNO)increased over 1000 times upon applying voltage without additional treatments.We observed persistent photoconductivity in 2D vertical heterostructure devices,attributed to charge trapping in QWs,and demonstrated artificial synaptic behaviours in a single flake with tailored energy consumption.Varying the number of perovskite layers significantly allows the tunability of the energy bandgap.This study also highlights the high tunability of 2D perovskite nanosheets,promising various applications,including magnetic,high-k dielectric,and resistive switching devices.Our findings suggest a new class of ionic layered materials with great potential as novel two-dimensional building blocks for device applications.展开更多
The electrochemical properties of a friction stir processed(FSPed)equiatomic CrMnFeCoNi high-entropy alloy(HEA)was investigated in an aerated 0.5 M Na_(2)SO_(4) electrolyte solution at room temperature.The microstruct...The electrochemical properties of a friction stir processed(FSPed)equiatomic CrMnFeCoNi high-entropy alloy(HEA)was investigated in an aerated 0.5 M Na_(2)SO_(4) electrolyte solution at room temperature.The microstructural analysis reveals a highly refined stir zone(SZ)with an average grain size that decreases from the top region of the SZ to the bottom region of the SZ(also known as shear-processed zone;SPZ).However,the region below the SPZ,(i.e.below the plunge depth)experienced an increase in average grain size and dislocation densities compared to the other regions.There is no secondary phase observed in the FSPed region,however,the microstructural evolution in the FSPed region affects the electrochemical behavior of the HEA.Cr_(2)O_(3) passive layer was observed to form on the FSPed HEA,leading to excellent corrosion properties from the polarization corrosion tests.Grain refinement in the SZ enhances the rapid formation of the passive layer,thus,leading to better corrosion properties in the front surface of the FSPed HEA.The localized corrosion behavior of the FSPed HEA was predicted to be caused by the micro-galvanic nature of the HEA,which leads to an increase in polarization at the anodic sites(pits).A numerical model was established using the corrosion parameters from the experiment to simulate the localized corrosion behavior on the surface of the FSPed HEA in a neutral environment.The predicted initial pitting potential and corresponding current density agree well with the experimental results.The model is also capable of tracking the dissolution of the pits over longer periods.展开更多
Resistive strain sensors(RSS)with ultrasensitivity have attracted much attention as multifunctional sensors.However,since most ultrasensitive RSS are designed by cracked conductive metals,the sensing performance is se...Resistive strain sensors(RSS)with ultrasensitivity have attracted much attention as multifunctional sensors.However,since most ultrasensitive RSS are designed by cracked conductive metals,the sensing performance is severely degraded due to accumulated structural deformation with consecutive cycles.To overcome such limitation,newly designed structures have been suggested,but the development of mechanosensors exhibiting superior stability and ultrasensitivity still remains a challenge.Here,we demonstrate that vertical graphene(VG)RSS with high sensitivity(gauge factor greater than 5000),remarkable durability(>10,000 cycles),and extraordinary resilience can serve multifunctional applications.We find that well-defined cracks on tufted network structure result in highly reversible resistance variation,especially revivable status even after broken current path,confirmed by microscopic in situ monitoring.The VG integrated with a wireless sensing system exhibits excellent timbre recognition performance.Our findings provide inspirable insights for mechanosensing system,making VG a promising component for future practicable flexible sensor technologies.展开更多
基金the financial support from Korea Institute of Energy Technology Evaluation and Planning(KETEP)grant funded by the Korea government(20214000000480)The support from the National Research Foundation of Korea funded by the Ministry of Education(No.2018R1A6A1A03024509 and NRF2020R1F1A1073885)is acknowledged.
文摘The mechanical behavior of a magnesium alloy E-form under bending was investigated using the elasto-visco-plastic polycrystal model(ΔEVPSC) and its finite element(FE) implementation(ΔEVPSC-FE) developed in Jeong et al. and Jeong and Tomé. The crystallographic orientation distribution(COD) obtained from X-ray diffraction was used to represent the initial texture, and the Voce hardening parameters were calibrated by fitting the uniaxial tension and the compression flow stress curves. A quasi-static FE analysis of a miniaturized V-bending operation was conducted using the ΔEVPSC-FE model. The bending induced an inhomogeneous stress response along the through-thickness and the lateral directions, which was well captured by the model. Moreover, the predictive capability of the model was validated by comparing with various experimental results such as(1) force vs. displacement curves;(2) the through-thickness variations in the twin volume fraction;and(3) the changes in crystallographic texture as a function of displacement. Additional bending simulation was performed using an isotropic texture, the result of which suggests that the potential improvement in bendability of the magnesium alloy is attainable by weakening the initial texture. Moreover, the simulation results imply that the crystallographic texture, which may affect the twin activation across the thickness direction, plays a significant role in the shifting direction of the neutral layer.
基金supported by the National Research Foundation (NRF) grant funded by the Korea government (NRF2022R1C1C1007619, NRF-2021M3H4A1A01002921, NRF2021M3I3A1084292)supported by the KIST Institutional Program (Project No. 2E32592-23-069)。
文摘PrBa_(0.5)Sr_(0.5)Co_(1.5)Fe_(0.5)O_(5+δ)(PrBSCF) has attracted much research interest as a potential triple ionic and electronic conductor(TIEC) electrode for protonic ceramic fuel cells(PCFCs). The chemical formula for Pr BSCF is AA'B_(2)O_(5+δ), with Pr(A-site) and Ba/Sr(A'-site) alternately stacked along the c-axis. Due to these structural features, the bulk oxygen ion diffusivity is significantly enhanced through the disorder-free channels in the PrO layer;thus, the A site cations(lanthanide ions) play a pivotal role in determining the overall electrochemical properties of layered perovskites. Consequently, previous research has predominantly focused on the electrical properties and oxygen bulk/surface kinetics of Ln cation effects,whereas the hydration properties for PCFC systems remain unidentified. Here, we thoroughly examined the proton uptake behavior and thermodynamic parameters for the hydration reaction to conclusively determine the changes in the electrochemical performances depending on LnBa_(0.5)Sr_(0.5)Co_(1.5)Fe_(0.5)O_(5+δ)(LnBSCF,Ln=Pr, Nd, and Gd) cathodes. At 500 ℃, the quantitative proton concentration of PrBSCF was 2.04 mol% and progressively decreased as the Ln cation size decreased. Similarly, the Gibbs free energy indicated that less energy was required for the formation of protonic defects in the order of Pr BSCF < Nd BSCF < Gd BSCF. To elucidate the close relationship between hydration properties and electrochemical performances in LnBSCF cathodes, PCFC single cell measurements and analysis of the distribution of relaxation time were further investigated.
基金supported by the Korea Institute of Science and Technology(No.2E30993).
文摘Absorption and desorption processes of hydrogen in metals are facilitated by alloying elements;however,the formation of secondary phases often reduces storage capacity.The alloying effect on the hydrogen kinetics has been examined by time-lag permeation measurement,which lacks spatial resolution and yields the averaged diffusion coefficient from multiple phases.Here,we report an advanced scanning Kelvin probe force microscopy,combined with in-situ hydrogen loading system for submicron-scale measurement of diffusion kinetics in metals.Successive probing of the surface during hydrogen loading detects the temporal and spatial variations in the surface potential,enabling the estimation of diffusion coefficient.Not only for a single-phase magnesium but also for multiphase titaniumiron based alloys,we can obtain the diffusion coefficients of hydrogen in each phase.The estimated diffusion coefficients for TiFe alloys are higher than that for the pristine TiFe intermetallic compound,due to alloying elements that reduce the diffusion barrier and modify bond character.Our approach paves the way to the microscopic understanding of hydrogen diffusion in metals.
基金supported by the National Research Foundation of Korea(NRF)grant funded by the government of the Republic of Korea(the Ministry of Science and ICT)(Nos.NRF-2023R1A2C2003247,2021R1C1C2091728,and 2021R1A2C2010695)the Nano&Material Technology Development Program through the National Research Foundation of Korea(NRF)funded by Ministry of Science and ICT(No.RS-2024-00402972)the National Research Council of Science&Technology(NST)grant by the Korea。
文摘The atomically thin nature of two-dimensional(2D)layered materials makes them susceptible to charge trapping by randomly created disorders,adversely affecting carrier dynamics such as charge transport and exciton lifetime.Typically,these disorders lead to poor device performance or require additional space to mitigate performance degradation.In this study,we investigate 2D layered Dion–Jacobson(DJ)-phase oxide perovskite nanosheets,which exhibit charge trapping within their well-defined quantum well(QW)structures,resulting in unique tailoring of electrical conductivity and photoconductivity.These DJ-phase perovskites,composed of tunable atomic constituents,demonstrate resonant tunneling and anomalous charge trapping due to their ultra-clean QWs.Remarkably,the conductivity of insulating HSr_(2)Nb_(3)O_(10)(HSNO)increased over 1000 times upon applying voltage without additional treatments.We observed persistent photoconductivity in 2D vertical heterostructure devices,attributed to charge trapping in QWs,and demonstrated artificial synaptic behaviours in a single flake with tailored energy consumption.Varying the number of perovskite layers significantly allows the tunability of the energy bandgap.This study also highlights the high tunability of 2D perovskite nanosheets,promising various applications,including magnetic,high-k dielectric,and resistive switching devices.Our findings suggest a new class of ionic layered materials with great potential as novel two-dimensional building blocks for device applications.
基金supported by the National Research Foundation of Korea(NRF)grants funded by the Ministry of Science and ICT(MSIT)(Nos.NRF-2018R1A5A1025224 and 2020R1A5A6017701)supported by the Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education(No.2020R1I1A3A04037992)。
文摘The electrochemical properties of a friction stir processed(FSPed)equiatomic CrMnFeCoNi high-entropy alloy(HEA)was investigated in an aerated 0.5 M Na_(2)SO_(4) electrolyte solution at room temperature.The microstructural analysis reveals a highly refined stir zone(SZ)with an average grain size that decreases from the top region of the SZ to the bottom region of the SZ(also known as shear-processed zone;SPZ).However,the region below the SPZ,(i.e.below the plunge depth)experienced an increase in average grain size and dislocation densities compared to the other regions.There is no secondary phase observed in the FSPed region,however,the microstructural evolution in the FSPed region affects the electrochemical behavior of the HEA.Cr_(2)O_(3) passive layer was observed to form on the FSPed HEA,leading to excellent corrosion properties from the polarization corrosion tests.Grain refinement in the SZ enhances the rapid formation of the passive layer,thus,leading to better corrosion properties in the front surface of the FSPed HEA.The localized corrosion behavior of the FSPed HEA was predicted to be caused by the micro-galvanic nature of the HEA,which leads to an increase in polarization at the anodic sites(pits).A numerical model was established using the corrosion parameters from the experiment to simulate the localized corrosion behavior on the surface of the FSPed HEA in a neutral environment.The predicted initial pitting potential and corresponding current density agree well with the experimental results.The model is also capable of tracking the dissolution of the pits over longer periods.
基金support from the National Research Foundation of Korea (NRF)grant funded by the Korean government (No.2016R1E1A1A01942649)support from the National Research Foundation of Korea (NRF)grant funded by the Korean government (2018R1D1A1B07048109 and 2021R1F1A1050726)+1 种基金support from the National Research Foundation of Korea (NRF)grant funded by the Korean government (grant nos.2018R1D1A1B07045581)from a Korea University Grant.
文摘Resistive strain sensors(RSS)with ultrasensitivity have attracted much attention as multifunctional sensors.However,since most ultrasensitive RSS are designed by cracked conductive metals,the sensing performance is severely degraded due to accumulated structural deformation with consecutive cycles.To overcome such limitation,newly designed structures have been suggested,but the development of mechanosensors exhibiting superior stability and ultrasensitivity still remains a challenge.Here,we demonstrate that vertical graphene(VG)RSS with high sensitivity(gauge factor greater than 5000),remarkable durability(>10,000 cycles),and extraordinary resilience can serve multifunctional applications.We find that well-defined cracks on tufted network structure result in highly reversible resistance variation,especially revivable status even after broken current path,confirmed by microscopic in situ monitoring.The VG integrated with a wireless sensing system exhibits excellent timbre recognition performance.Our findings provide inspirable insights for mechanosensing system,making VG a promising component for future practicable flexible sensor technologies.
