arXiv subjects

Aijun Hong

Publications and source records attributed to Aijun Hong.

9 recordsLinked to original sources

arXiv2025

Ta2Pd3Te8: A potential candidate of 1D van der Waals stacked thermoelectric materials

Discovering new thermoelectric (TE) materials is an eternal goal in the TE field. Excellent TE materials have ranged from 3D stacked to 2D stacked bulk. However, the 1D stacked receives little attention due to the scarcity in quantity. In this work, it is predicted that 1D van der Waals (vdW) stacked Ta2Pd3Te8 crystal is a compelling candidate for TE applications by combining first-principles calculations with phonon and electron Boltzmann transport equations and molecular dynamics methods. We find that Ta2Pd3Te8 crystal has mechanical, dynamical, and thermal stabilities, and its TE properties are featured by strong anisotropy, high power factor (PF) and low lattice thermal conductivity. The results indicate the ZT values of n-type Ta2Pd3Te8 at 900 K along a, b and c axes reach 0.48, 0.39 and 0.22, respectively. We propose that enlarging the bandgap can weaken the bipolar effect and thus significantly increases ZT to 1.11. The findings in the work not only stimulate more theoretical works on 1D vdW stacked TE materials, but also provide valuable information for experimentally improving TE materials.

cond-mat.mtrl-sci↗

arXiv2025

Crystal structures and electronic and magnetic properties of Janus bilayer Cl3Cr2I3

Two-dimensional (2D) magnetic material CrI3 has aroused extensive attention, because it could provide a new platform for investigating the relations between crystal structures and electronic and magnetic properties. Here, we study crystal structures and electronic and magnetic properties of three configurations (Cl-Cl I-I and Cl-I) of Janus bilayer Cl3Cr2I3 with two stacking orders (AB and AA1=3) by using the first principles approach incorporating the spin-orbit coupling (SOC) effect and the dipole correction. It is found that the spin polarization and the SOC effect can expand the lattice constant and the interlayer distance (ID) of the three configurations. Especially, the ID of the I-I configuration is 1 {\AA} larger than that of the Cl-Cl configuration. The total energy calculation results show that the atomic configuration, the SOC effect and the stacking order play an important role in determining the magnetic ground states of the Janus layers. Our results indicate the atomic configurations of the Janus bilayers are not conducive to the increase of critical temperature. Interestingly, the Cl-I configuration has a vertical dipole moment, and its AFM state has large spin splitting. It is revealed that the non-periodic structure, the symmetry breaking of the average potential and the weak interlayer interaction lead to the vertical dipole moment and the abnormal AFM state that is not the most stable state.

cond-mat.mtrl-sci↗

arXiv2023

Re-understanding of the deformation potential constant in the single crystal silicon

The mobility formula based on deformation potential (DP) theory is of great importance in semiconductor physics. However, the related calculations for the DP constant are controversial. It is necessary to redo in-depth and comprehensive research on the mobility of single crystal silicon and the related parameters such as the effective mass and the DP constant. In this work the conductivity effective mass is redefined and a method based on the first principles is presented to evaluate the correction of the DP constant. It is found that the effective mass is closer to experimental data and the correction of the DP is a negligible value of about 0.3 eV. Using these parameters, we obtain the mobilities of the single crystal silicon in reasonable agreement with the experimental values. Our method can be effectively applied to the prediction for the mobility in bulk materials.

cond-mat.mtrl-sci↗

arXiv2021

High-throughput screening of quaternary compounds and new insight for excellent thermoelectric performance

It is well known that the high electric conductivity, large Seebeck coefficient, and low thermal conductivity are preferred for enhancing thermoelectric performance, but unfortunately, these properties are strongly inter-correlated with no rational scenario for their efficient decoupling. This big dilemma for thermoelectric research appeals for alternative strategic solutions, while the high-throughput screening is one of them. In this work, we start from total 3136 real electronic structures of the huge X2YZM4 quaternary compound family and perform the high-throughput searching in terms of enhanced thermoelectric properties. The comprehensive data-mining allows an evaluation of the electronic and phonon characteristics of those promising thermoelectric materials. More importantly, a new insight that the enhanced thermoelectric performance benefits substantially from the coexisting quasi-Dirac and heavy fermions plus strong optical-acoustic phonon hybridization, is proposed. This work provides a clear guidance to theoretical screening and experimental realization and thus towards development of performance-excellent thermoelectric materials.

physics.app-ph↗

arXiv2020

Influence of different exchange-correlation potentials on twisted structures of bilayer XS2 (X= Mo, Cr)

In this work, we employ the LDA, GGA and GGA with four vdW corrections to study crystal and electronic structures of bilayer transition metal dichalcogenides (TMDs) with different twist angles. We find the GGA interlayer distance of bilayer MoS2 has good agreement with experimental value while vdW correction method still needs to be further improved. Our results indicate the GGA interlayer distances of bilayer XS2 (X= Mo, Cr) with twist angles are smaller than that of normal bilayer, which is the opposite in the LDA case. The GGA results show that reduced bandgap is due to the reduction of interlayer distance and, flat valley and conductivity bands appear owing to twist angle. Our study not only supports valuable information for application possibility of twisted two-dimensional (2D) materials but also stimulates more related research.

cond-mat.mtrl-sci↗

arXiv2020

Prediction for structure stability and ultrahigh hydrogen evolution performance of monolayer 2H-CrS2

By a combination of the first-principles calculations and climbing image nudged elastic band method (ciNEB) we investigate structure stabilities and hydrogen evolution reaction (HER) performance of monolayer 2H-CrS2. The results suggest the free energy for the Volmer reaction in the monolayer 2H-CrS2 with S vacancy is 0.07 eV, comparable with Pt-based catalyst, and HER on the surface of the monolayer is prone to the Volmer-Heyrovsky mechanism with no energy barrier. We propose that high HER performance stems from the reduction of the energy level of d-band center. Additionally, the S vacancy leads to defect states in the middle of electronic bandgap and the reduction of potential barrier between the S atom layer and the vacuum, which is conducive to improve HER performance.

cond-mat.mtrl-sci↗

arXiv2020

Effects of biaxial strain and local constant potential on electronic structure of monolayer SnSe

We use the modified Becke-Johnson exchange potential (mBJ) with the spin-orbit coupling effect (SOC) to study effects of biaxial strain and local constant potential on electronic structure of monolayer SnSe. Our results show the fundamental band gap size can be tuned via biaxial strain. Compressive strain (tensile strain) can narrow (enlarge) band gap, and compressive strain causes the transition from quasi-direct to indirect band gap. Moreover, considering that any tuning of electronic structure is realized by changing the periodic potential distribution in the crystalline, we directly add constant potential (CP) to muffin-tin spheres. The results demonstrate that positive and negative CPs can narrow and enlarge band gap, respectively. At CP of 0.9 Ry, semiconductor-metal transition appears, and interestingly a new type of nearly linear dispersions occur at band edge. Our work is good for inspiring more experimental and further theoretical research works.

cond-mat.mtrl-sci↗

arXiv2019

Large enhancement of infrared absorption due to trimer comprised of doping-N and S-S divacancies in the imperfect monolayer MoS2: A first-principles study

In this study, we systematically study on crystal and electronic structures and optical absorption properties of perfect monolayer MoS2 (M), M with S vacancy (M@SV), M with N doping at S site (M@ND) and M with both S vacancy and N doping at S site (M@V-D) using first-principles method. It is showed that the N atom is tend to located between Mo and S layers, leaving one vacancy at original site, to form interstitial N atom. Thus, the interstitial N atom and the S vacancy make up the NI-VS dimer. We study M@V-D with five atomic configurations and find the most stable structure having the NI-VS-VS trimer. It is showed that the absorbance for the stable M@V-D in the most infrared region is obviously higher than that for the other systems. It is revealed that large enhancement of infrared absorption for the stable M@V-D is mainly attributable to the special electronic structure determined by the crystal structure with the trimer. It is considered that M@V-D could be the promising candidate for infrared materials.

cond-mat.mtrl-sci↗

arXiv2015

Optimizing thermoelectric performances of low-temperature SnSe compounds by electronic structure design

Recently SnSe compound was reported to have a peak thermoelectric figure-5 of-merit (ZT) of 2.62 at 923 K, but the ZT values at temperatures below 750 K are relatively low. In this work, the electronic structures of SnSe are calculated using the density functional theory, and the electro- and thermo-transport properties upon varying chemical potential (or carrier density) are evaluated by the semi-classic Boltzmann transport theory, showing that the calculated ZT values along the a10 and c-axes below 675 K are in agreement with reported values, but that along the b-axis can be as high as 2.57 by optimizing the carrier concentration to ~3.6*1019 cm-3. It is revealed that a mixed ionic-covalent bonding and heavy-light band overlapping near the valence band are the reasons for the higher thermoelectric performance

cond-mat.mtrl-sci↗