Van An Dinh - Academia.edu (original) (raw)

Papers by Van An Dinh

Chemical Engineering Journal

VNU Journal of Science: Mathematics - Physics, 2020

In this work, we investigate the defect structure of Silicene with a vancacy and the adsorption... more In this work, we investigate the defect structure of Silicene with a vancacy and the adsorption mechanism of isopropanol on the surface of defected Silicene by employing the Density Functional Theory method. The adsorption profile was determined based on van der Waals functional optPBE-vdW and the charge transfer between isopropanol and silicene this system was also calculated by Bader charge analysis method. In the defected Silicene, Si vacancy preferably forms on the lower layer of the bulking structure. As a Si vacancy is introduced, Silicene exhibits a metallic behavior with zero bandgap. Due to the losing electron of defected Silicene, isopropanol is adsorbed on the surface with the most favourable adsorption configuration in which oxygen atom towards the surface of Silicene. Isopropanol adsorption opens a tunnelling gap of defected Silicence, resulting in the mili-gap characteristics of the adsorbed Silicene system. The adsorption profile of this volatile organic compound on...

VNU Journal of Science: Mathematics - Physics, 2020

Borophene, a new member of the 2D material family, was proven theoretically and empirically in ma... more Borophene, a new member of the 2D material family, was proven theoretically and empirically in many recent studies that it has a unique structure and promising properties applied in batteries and electronic devices. In this work, the adsorbability of β12 – borophene towards some main poisonous gases was investigated. Herein, first-principle calculations were employed to obtain the adsorption configurations, adsorption energy of CO, NO, CO2, NH3, and NO2 on b12 – borophene by using three van der Waals correlation functionals: revPBE-vdW, optPBE-vdW, and vdW-DF2. Also, the most stable configurations and diffusion possibilities of the gas molecules on the surface of b12 – borophene were determined visually by using Computational DFT-based Nanoscope. The nature of bonding and interaction between gas molecules and b12 – borophene were disclosed by using the density of states analysis and Bader charge analysis. Remarkably, borophene exhibits as a highly selective adsorbent when having gre...

VNU Journal of Science: Mathematics - Physics, 2020

In this work, we investigated the adsorption mechanism of acetone and toluene on the surface of s... more In this work, we investigated the adsorption mechanism of acetone and toluene on the surface of silicene by the quantum simulation method. The images of the potential energy surfaces for different positions of the adsorbate on the silicene surface were explored by Computational DFT-based Nanoscope tool for determination of the most stable configurations and diffusion possibilities. The charge transfer in order of 0.2 – 0.3 electrons and the tunneling gap opening of 18 – 23 meV due to acetone and toluene, respectively, suggest that silicene is considerably sensitive with these VOCs and can be used as the material in the fabrication of reusable VOC sensors.

ACS Sustainable Chemistry & Engineering, Apr 19, 2023

AIP Advances

We study the band valley modification induced by isotropic strain in monolayer WSe2 using the non... more We study the band valley modification induced by isotropic strain in monolayer WSe2 using the non-local van der Waals density functionals theory including the spin–orbit coupling effect. The dominant contributions of orbitals to the band extrema, spin splitting, and exciton diversity in monolayer WSe2 are visually displayed. The vertical shift of the d and p partial orbitals of W and Se atoms, respectively, at band edges under strain results in a notable reduction of the bandgap. Under tensile strain, the deformations of the band valleys lead to an additional appearance of optical excitons and the disappearance of momentum excitons. Therefore, the experimental observations of the changes in the radiation spectra such as the redshift of A and B excitons, blueshift of C and D excitons, enhancement of intensity, localization, and symmetrization of the exciton resonances can be explained thoroughly. Under compression, the band valley modification may lead to an additional appearance of ...

Applied Surface Science, 2021

ECS Meeting Abstracts, 2020

In transition metal-based cathode materials, the oxidation and reduction of transition metal ions... more In transition metal-based cathode materials, the oxidation and reduction of transition metal ions cause local distortion in the crystal structure during intercalation and de-intercalation, resulting in the formation of a quasiparticle, named small polaron. Since a strong binding energy of 500 meV between an alkali ion and a small polaron was reported[1], the polaron would migrate simultaneously with the diffusion of the alkali ions[2]. Using the density functional method, we investigate the crystal, electronic structure, and electrochemical properties of orthorhombic NaxVPO5 and NaxVPO4F, focusing on the diffusion mechanism of a Na ion accompanied with polaron. The diffusion of Na ions can be described as a process of the complex of the Na vacancy and accompanying positive polaron at high Na concentrations and as that of the Na ion and negative polaron at low Na concentrations. When a Na vacancy is introduced to fully occupied structure (x=1), the positive small polaron prefers loca...

Lithium-Related Batteries, 2022

Materials Science in Semiconductor Processing, 2021

Abstract Na ion batteries (SIBs) have attained tremendous consideration due to their environmenta... more Abstract Na ion batteries (SIBs) have attained tremendous consideration due to their environmental friendliness, natural abundance and low costs. In this study, the electronic and electrochemical characteristics of SnSe2 monolayer for SIBs are investigated by using first principle calculations. The electronic structure of 2D SnSe2 exhibit semiconducting character with band gap of 0.85 eV and 1.4 eV by using PBE-GGA and HSE06 schemes, respectively. Our computation revealed that Na adsorbed SnSe2 system demonstrate metallic characteristics. With rise of Na loading, the electronic conductivity of the host materials upsurges. An average open circuit voltage (OCV) of 0.662 V is perceived with Na storage capacity of 387 mAhg−1. This capacity is greater than the commercial anode materials (i.e. graphite has storage capacity of 372 mAhg−1 and 273 mAhg−1 for LIBs and KIBs, respectively). Furthermore, a significantly low activation energy (104 meV) for Na diffusion on the SnSe2 monolayer surface is obtained. Hence, these outcomes suggest that SnSe2 monolayer is a potential applicant for SIBs.

Physical Chemistry Chemical Physics, 2019

The rapidly rising demand for energy storage systems presents an imperative need to develop sodiu... more The rapidly rising demand for energy storage systems presents an imperative need to develop sodium-ion batteries with high energy density, high conductivity, and low barrier energy.

The Japan Society of Applied Physics, 2013

2 Faculty of pure and applied physics, Tsukuba University E-mail: DINH.Anvan@nims.go.jp Rechargea... more 2 Faculty of pure and applied physics, Tsukuba University E-mail: DINH.Anvan@nims.go.jp Rechargeable Li-ion batteries have been widely used as a power source for mobile electronic devices and expected to be a promising power source for electric motor cycles, electric vehicles and the smart grid system. Today, many attempts have been made to improve the cathode performance or design a new cathode material. However, the materials used for the cathode still lack some requirements such as the power density, ionic conductivity, cost and friendliness with environment. To overcome these, the proper explanation of the electrochemical properties, diffusion mechanism inside the materials is urgently needed. In this work, we present a new insight of Li ion diffusion in the cathode materials based on the first principle calculation[1]. The diffusion of Li vacancy and its accompanying polaron is treated as the process of the polaron-Li vacancy complex. The diffusion mechanism is explained upon t...

The Japan Society of Applied Physics, 2014

Dinh Van An , Sato Kazunori, Katayama-Yoshida Hiroshi and Kakeshita Tomoyuki E-mail: divan@mat.en... more Dinh Van An , Sato Kazunori, Katayama-Yoshida Hiroshi and Kakeshita Tomoyuki E-mail: divan@mat.eng.osaka-u.ac.jp 1 Graduate School of Engineering, Osaka Univ.. 2 Graduate School of Engineering Science, Osaka Univ. Abstract The prototype dilute magnetic semiconductor GaMnAs has been discovered [1] and investigated during two decades. Previously, ferromagnetism in this material has been known to be induced by the p-d exchange interaction of the valence holes and localized d-electrons of Mn atoms [2], and the Zener p-d exchange interaction model has been widely accepted as the main mechanism inducing ferromagnetism in GaMnAs [3]. Following this model, the d-orbitals of Mn atoms hybridize the p-orbitals of As atoms and form an Mn-induced impurity band (IB) that merges with the valence band (VB) to expand VB towards the bandgap, and the Fermi level (EF) lies in the merged VB. Recently, besides many experimental works support this model, several experiments have reported that EF locates i...

MATERIALS TRANSACTIONS, 2020

In this work, we investigated the adsorption mechanism of acetone and toluene on the surface of s... more In this work, we investigated the adsorption mechanism of acetone and toluene on the surface of single-vacancy silicene by Density Functional Theory method with taking into account the van der Waals interaction via the optPBE-vdW functional. The potential energy surface and adsorption energy profile are obtained by using the Computational DFTbased Nanoscope tool. It is found that acetone prefers an inclined configuration while toluene favors the parallel one towards the substrate. The single-vacancy silicene maintains its metallic electronic structure after adsorption. The adsorption energies for acetone and toluene adsorptions are ¹0.36 eV and ¹0.57 eV, respectively. The Bader charge analysis shows a charge transfer of 0.17e and 0.30e for adsorption of acetone and toluene on silicene, respectively.

The European Physical Journal Plus

Journal of Physics: Condensed Matter

Active enhancement of the optical absorption coefficient to improve the light converting efficien... more Active enhancement of the optical absorption coefficient to improve the light converting efficiency of thin-film solar cell materials is crucial to develop the next-generation solar cell devices. Here we report first-principles calculations with generalized gradient approximation to study the optoelectronic properties of pristine and divacancy (DV) blue phosphorene (BlueP) thin films under structural deformation. We show that instead of forming sp-like covalent bonds as in the pristine BlueP layer, a DV introduces two particular dangling bonds between the voids. Using a microscopic (non-) affine deformation model, we reveal that the orbital hybridization of these dangling bonds is strongly modified in both the velocity and vorticity directions depending on the type of deformation, creating an effective light trap to enhance the material absorption efficiency. Furthermore, this successful light trap is complemented by a clear signature of σ + π plasmon when a DV BlueP layer is slight...

Physical Review Materials, 2022

The P2-layered oxide NaMnO 2 is known as a cheap and high-capacity material for secondary batteri... more The P2-layered oxide NaMnO 2 is known as a cheap and high-capacity material for secondary batteries, but has been limited in application due to the large Jahn-Teller lattice distortion. Through the highly accurate hybrid functional method (HSE06), we computationally evaluate the doping influences on the lattice distortions, stabilities, electronic structures, redox potentials, and diffusion mechanisms. Our calculations indicate that dopants not only reduce the lattice distortion degree, especially for Li, Mg, Ti, and V cases, but also increase the stability of the structure, implying the dopants would alleviate the Jahn-Teller lattice distortion. At low Na concentrations, the Li dopant preferably diffuses out of the MnO 2 layer, but hardly moves to the Na layer, suggesting that P2-layered oxides can prevent the dopant's migrations during the Na extractions. At full Na concentrations, all the considered dopants, except for Ti and V, have a small effect on the redox potential. The effect on the diffusion mechanism is described through the diffusion of a Na ion-polaron complex near the dopant's environments. Fe, Mg, Ti, and Cr dopants can hinder the Na ion-polaron complex diffusion with significantly higher activation energies, respectively, while the Al dopant almost remains the activation energy as well as the perfect structure. However, Li, V, Co, and Ni dopants benefit from such complex diffusion with much lower activation energy so the ion diffusivities increase significantly. It is found that the doping influence on the activation energy for Na ion diffusion is associated with the M-O bond change and charges of the neighboring dopants.

Journal of Alloys and Compounds, 2021

Abstract We theoretically propose novel orthorhombic phase of tavorite-like AxVPO4F cathodes (A =... more Abstract We theoretically propose novel orthorhombic phase of tavorite-like AxVPO4F cathodes (A = Li, Na and 0 ≤x≤ 1) applicable for Li-ion and Na-ion batteries. Phase stability, electronic structures, electrochemical properties, and diffusion mechanisms of A ions and vacancies of AxVPO4F are clarified using the density functional method. Both LiVPO4F and NaVPO4F would experience bi-phase reactions upon the A extractions for 0.125 ≤x≤ 0.5 and 0.5 ≤x≤ 1, and exhibit high voltages of 4.12 and 3.80 V and the high capacities of 156 and 143 mAhg−1, respectively. The effect of small polaron on the ion diffusion mechanism is carefully addressed. The activation energies of Na ion diffusion gain 323 and 530 meV whilst they lower to 95 and 240 meV for Li ion diffusion in the Na/Li-rich and poor phases, respectively. Therefore, the proposed cathodes can be expected to exhibit significantly faster Li/Na-ion diffusion than that in popular cathodes such as lithium olivine phosphate LiFePO4 (430 meV), high-rate triclinic LiVPO4F (418 meV) and NaVOPO4 (627 meV).

Computational Materials Science, 2008

We present a first principle study of new class of high-Tc half-heusler ferromagnets NiCrZ (Z = S... more We present a first principle study of new class of high-Tc half-heusler ferromagnets NiCrZ (Z = Si, P, Ge, As, Te). The structure and magnetic properties are investigated through the calculation of the electronic structure, equilibrium lattice constant, magnetic exchange interaction Jij and Curie temperature Tc. The role of sp-elements and the influence of lattice expansion/compression are also studied. In alloys having 20 valence electrons, a pseudo-gap of the majority band can be formed at Fermi level. Otherwise, the half-metallicity and ferromagnetism at temperatures much higher than room temperature are found to be stable in a wide range of lattice expansion. Based on these results, NiCrZ can be expected to be promising materials for spintronics. ∗Electronic address: divan@cmp.sanken.osaka-u.ac.jp.

Chemical Engineering Journal

VNU Journal of Science: Mathematics - Physics, 2020

In this work, we investigate the defect structure of Silicene with a vancacy and the adsorption... more In this work, we investigate the defect structure of Silicene with a vancacy and the adsorption mechanism of isopropanol on the surface of defected Silicene by employing the Density Functional Theory method. The adsorption profile was determined based on van der Waals functional optPBE-vdW and the charge transfer between isopropanol and silicene this system was also calculated by Bader charge analysis method. In the defected Silicene, Si vacancy preferably forms on the lower layer of the bulking structure. As a Si vacancy is introduced, Silicene exhibits a metallic behavior with zero bandgap. Due to the losing electron of defected Silicene, isopropanol is adsorbed on the surface with the most favourable adsorption configuration in which oxygen atom towards the surface of Silicene. Isopropanol adsorption opens a tunnelling gap of defected Silicence, resulting in the mili-gap characteristics of the adsorbed Silicene system. The adsorption profile of this volatile organic compound on...

VNU Journal of Science: Mathematics - Physics, 2020

Borophene, a new member of the 2D material family, was proven theoretically and empirically in ma... more Borophene, a new member of the 2D material family, was proven theoretically and empirically in many recent studies that it has a unique structure and promising properties applied in batteries and electronic devices. In this work, the adsorbability of β12 – borophene towards some main poisonous gases was investigated. Herein, first-principle calculations were employed to obtain the adsorption configurations, adsorption energy of CO, NO, CO2, NH3, and NO2 on b12 – borophene by using three van der Waals correlation functionals: revPBE-vdW, optPBE-vdW, and vdW-DF2. Also, the most stable configurations and diffusion possibilities of the gas molecules on the surface of b12 – borophene were determined visually by using Computational DFT-based Nanoscope. The nature of bonding and interaction between gas molecules and b12 – borophene were disclosed by using the density of states analysis and Bader charge analysis. Remarkably, borophene exhibits as a highly selective adsorbent when having gre...

VNU Journal of Science: Mathematics - Physics, 2020

In this work, we investigated the adsorption mechanism of acetone and toluene on the surface of s... more In this work, we investigated the adsorption mechanism of acetone and toluene on the surface of silicene by the quantum simulation method. The images of the potential energy surfaces for different positions of the adsorbate on the silicene surface were explored by Computational DFT-based Nanoscope tool for determination of the most stable configurations and diffusion possibilities. The charge transfer in order of 0.2 – 0.3 electrons and the tunneling gap opening of 18 – 23 meV due to acetone and toluene, respectively, suggest that silicene is considerably sensitive with these VOCs and can be used as the material in the fabrication of reusable VOC sensors.

ACS Sustainable Chemistry & Engineering, Apr 19, 2023

AIP Advances

We study the band valley modification induced by isotropic strain in monolayer WSe2 using the non... more We study the band valley modification induced by isotropic strain in monolayer WSe2 using the non-local van der Waals density functionals theory including the spin–orbit coupling effect. The dominant contributions of orbitals to the band extrema, spin splitting, and exciton diversity in monolayer WSe2 are visually displayed. The vertical shift of the d and p partial orbitals of W and Se atoms, respectively, at band edges under strain results in a notable reduction of the bandgap. Under tensile strain, the deformations of the band valleys lead to an additional appearance of optical excitons and the disappearance of momentum excitons. Therefore, the experimental observations of the changes in the radiation spectra such as the redshift of A and B excitons, blueshift of C and D excitons, enhancement of intensity, localization, and symmetrization of the exciton resonances can be explained thoroughly. Under compression, the band valley modification may lead to an additional appearance of ...

Applied Surface Science, 2021

ECS Meeting Abstracts, 2020

In transition metal-based cathode materials, the oxidation and reduction of transition metal ions... more In transition metal-based cathode materials, the oxidation and reduction of transition metal ions cause local distortion in the crystal structure during intercalation and de-intercalation, resulting in the formation of a quasiparticle, named small polaron. Since a strong binding energy of 500 meV between an alkali ion and a small polaron was reported[1], the polaron would migrate simultaneously with the diffusion of the alkali ions[2]. Using the density functional method, we investigate the crystal, electronic structure, and electrochemical properties of orthorhombic NaxVPO5 and NaxVPO4F, focusing on the diffusion mechanism of a Na ion accompanied with polaron. The diffusion of Na ions can be described as a process of the complex of the Na vacancy and accompanying positive polaron at high Na concentrations and as that of the Na ion and negative polaron at low Na concentrations. When a Na vacancy is introduced to fully occupied structure (x=1), the positive small polaron prefers loca...

Lithium-Related Batteries, 2022

Materials Science in Semiconductor Processing, 2021

Abstract Na ion batteries (SIBs) have attained tremendous consideration due to their environmenta... more Abstract Na ion batteries (SIBs) have attained tremendous consideration due to their environmental friendliness, natural abundance and low costs. In this study, the electronic and electrochemical characteristics of SnSe2 monolayer for SIBs are investigated by using first principle calculations. The electronic structure of 2D SnSe2 exhibit semiconducting character with band gap of 0.85 eV and 1.4 eV by using PBE-GGA and HSE06 schemes, respectively. Our computation revealed that Na adsorbed SnSe2 system demonstrate metallic characteristics. With rise of Na loading, the electronic conductivity of the host materials upsurges. An average open circuit voltage (OCV) of 0.662 V is perceived with Na storage capacity of 387 mAhg−1. This capacity is greater than the commercial anode materials (i.e. graphite has storage capacity of 372 mAhg−1 and 273 mAhg−1 for LIBs and KIBs, respectively). Furthermore, a significantly low activation energy (104 meV) for Na diffusion on the SnSe2 monolayer surface is obtained. Hence, these outcomes suggest that SnSe2 monolayer is a potential applicant for SIBs.

Physical Chemistry Chemical Physics, 2019

The rapidly rising demand for energy storage systems presents an imperative need to develop sodiu... more The rapidly rising demand for energy storage systems presents an imperative need to develop sodium-ion batteries with high energy density, high conductivity, and low barrier energy.

The Japan Society of Applied Physics, 2013

2 Faculty of pure and applied physics, Tsukuba University E-mail: DINH.Anvan@nims.go.jp Rechargea... more 2 Faculty of pure and applied physics, Tsukuba University E-mail: DINH.Anvan@nims.go.jp Rechargeable Li-ion batteries have been widely used as a power source for mobile electronic devices and expected to be a promising power source for electric motor cycles, electric vehicles and the smart grid system. Today, many attempts have been made to improve the cathode performance or design a new cathode material. However, the materials used for the cathode still lack some requirements such as the power density, ionic conductivity, cost and friendliness with environment. To overcome these, the proper explanation of the electrochemical properties, diffusion mechanism inside the materials is urgently needed. In this work, we present a new insight of Li ion diffusion in the cathode materials based on the first principle calculation[1]. The diffusion of Li vacancy and its accompanying polaron is treated as the process of the polaron-Li vacancy complex. The diffusion mechanism is explained upon t...

The Japan Society of Applied Physics, 2014

Dinh Van An , Sato Kazunori, Katayama-Yoshida Hiroshi and Kakeshita Tomoyuki E-mail: divan@mat.en... more Dinh Van An , Sato Kazunori, Katayama-Yoshida Hiroshi and Kakeshita Tomoyuki E-mail: divan@mat.eng.osaka-u.ac.jp 1 Graduate School of Engineering, Osaka Univ.. 2 Graduate School of Engineering Science, Osaka Univ. Abstract The prototype dilute magnetic semiconductor GaMnAs has been discovered [1] and investigated during two decades. Previously, ferromagnetism in this material has been known to be induced by the p-d exchange interaction of the valence holes and localized d-electrons of Mn atoms [2], and the Zener p-d exchange interaction model has been widely accepted as the main mechanism inducing ferromagnetism in GaMnAs [3]. Following this model, the d-orbitals of Mn atoms hybridize the p-orbitals of As atoms and form an Mn-induced impurity band (IB) that merges with the valence band (VB) to expand VB towards the bandgap, and the Fermi level (EF) lies in the merged VB. Recently, besides many experimental works support this model, several experiments have reported that EF locates i...

MATERIALS TRANSACTIONS, 2020

In this work, we investigated the adsorption mechanism of acetone and toluene on the surface of s... more In this work, we investigated the adsorption mechanism of acetone and toluene on the surface of single-vacancy silicene by Density Functional Theory method with taking into account the van der Waals interaction via the optPBE-vdW functional. The potential energy surface and adsorption energy profile are obtained by using the Computational DFTbased Nanoscope tool. It is found that acetone prefers an inclined configuration while toluene favors the parallel one towards the substrate. The single-vacancy silicene maintains its metallic electronic structure after adsorption. The adsorption energies for acetone and toluene adsorptions are ¹0.36 eV and ¹0.57 eV, respectively. The Bader charge analysis shows a charge transfer of 0.17e and 0.30e for adsorption of acetone and toluene on silicene, respectively.

The European Physical Journal Plus

Journal of Physics: Condensed Matter

Active enhancement of the optical absorption coefficient to improve the light converting efficien... more Active enhancement of the optical absorption coefficient to improve the light converting efficiency of thin-film solar cell materials is crucial to develop the next-generation solar cell devices. Here we report first-principles calculations with generalized gradient approximation to study the optoelectronic properties of pristine and divacancy (DV) blue phosphorene (BlueP) thin films under structural deformation. We show that instead of forming sp-like covalent bonds as in the pristine BlueP layer, a DV introduces two particular dangling bonds between the voids. Using a microscopic (non-) affine deformation model, we reveal that the orbital hybridization of these dangling bonds is strongly modified in both the velocity and vorticity directions depending on the type of deformation, creating an effective light trap to enhance the material absorption efficiency. Furthermore, this successful light trap is complemented by a clear signature of σ + π plasmon when a DV BlueP layer is slight...

Physical Review Materials, 2022

The P2-layered oxide NaMnO 2 is known as a cheap and high-capacity material for secondary batteri... more The P2-layered oxide NaMnO 2 is known as a cheap and high-capacity material for secondary batteries, but has been limited in application due to the large Jahn-Teller lattice distortion. Through the highly accurate hybrid functional method (HSE06), we computationally evaluate the doping influences on the lattice distortions, stabilities, electronic structures, redox potentials, and diffusion mechanisms. Our calculations indicate that dopants not only reduce the lattice distortion degree, especially for Li, Mg, Ti, and V cases, but also increase the stability of the structure, implying the dopants would alleviate the Jahn-Teller lattice distortion. At low Na concentrations, the Li dopant preferably diffuses out of the MnO 2 layer, but hardly moves to the Na layer, suggesting that P2-layered oxides can prevent the dopant's migrations during the Na extractions. At full Na concentrations, all the considered dopants, except for Ti and V, have a small effect on the redox potential. The effect on the diffusion mechanism is described through the diffusion of a Na ion-polaron complex near the dopant's environments. Fe, Mg, Ti, and Cr dopants can hinder the Na ion-polaron complex diffusion with significantly higher activation energies, respectively, while the Al dopant almost remains the activation energy as well as the perfect structure. However, Li, V, Co, and Ni dopants benefit from such complex diffusion with much lower activation energy so the ion diffusivities increase significantly. It is found that the doping influence on the activation energy for Na ion diffusion is associated with the M-O bond change and charges of the neighboring dopants.

Journal of Alloys and Compounds, 2021

Abstract We theoretically propose novel orthorhombic phase of tavorite-like AxVPO4F cathodes (A =... more Abstract We theoretically propose novel orthorhombic phase of tavorite-like AxVPO4F cathodes (A = Li, Na and 0 ≤x≤ 1) applicable for Li-ion and Na-ion batteries. Phase stability, electronic structures, electrochemical properties, and diffusion mechanisms of A ions and vacancies of AxVPO4F are clarified using the density functional method. Both LiVPO4F and NaVPO4F would experience bi-phase reactions upon the A extractions for 0.125 ≤x≤ 0.5 and 0.5 ≤x≤ 1, and exhibit high voltages of 4.12 and 3.80 V and the high capacities of 156 and 143 mAhg−1, respectively. The effect of small polaron on the ion diffusion mechanism is carefully addressed. The activation energies of Na ion diffusion gain 323 and 530 meV whilst they lower to 95 and 240 meV for Li ion diffusion in the Na/Li-rich and poor phases, respectively. Therefore, the proposed cathodes can be expected to exhibit significantly faster Li/Na-ion diffusion than that in popular cathodes such as lithium olivine phosphate LiFePO4 (430 meV), high-rate triclinic LiVPO4F (418 meV) and NaVOPO4 (627 meV).

Computational Materials Science, 2008

We present a first principle study of new class of high-Tc half-heusler ferromagnets NiCrZ (Z = S... more We present a first principle study of new class of high-Tc half-heusler ferromagnets NiCrZ (Z = Si, P, Ge, As, Te). The structure and magnetic properties are investigated through the calculation of the electronic structure, equilibrium lattice constant, magnetic exchange interaction Jij and Curie temperature Tc. The role of sp-elements and the influence of lattice expansion/compression are also studied. In alloys having 20 valence electrons, a pseudo-gap of the majority band can be formed at Fermi level. Otherwise, the half-metallicity and ferromagnetism at temperatures much higher than room temperature are found to be stable in a wide range of lattice expansion. Based on these results, NiCrZ can be expected to be promising materials for spintronics. ∗Electronic address: divan@cmp.sanken.osaka-u.ac.jp.