indirect band gap
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Author(s):  
Shanmugapriya V ◽  
Bharathi S ◽  
Esakkinaveen D ◽  
Arunpandiyan S ◽  
Selvakumar B ◽  
...  

Abstract The effect of pressure on the electronic and optical properties of SrAl2O4 up to 25 GPa was studied by means of the pseudo-potential plane waves method within the generalized gradient approximation for exchange and correlation. The calculated lattice parameters are consistent with available experimental and theoretical data. By analyzing the electronic and optical properties, the pressure dependences of the electronic structures and optical constants were investigated. The band structures show an indirect band gap for this compound and the calculated band gaps expend with increasing pressure. Meanwhile, the optical properties including the dielectric spectra, absorption coefficient spectra, reflectivity, and the real part of the refractive index spectra in the low energy range have a blue shift. Given this, the optical properties of SrAl2O4 could be tuned by changing pressure to some degree, which is beneficial to the optical applications.


Author(s):  
Hua Liang

Abstract The effect of pressure on the electronic and optical properties of SrAl2O4 up to 25 GPa was studied by means of the pseudo-potential plane waves method within the generalized gradient approximation for exchange and correlation. The calculated lattice parameters are consistent with available experimental and theoretical data. By analyzing the electronic and optical properties, the pressure dependences of the electronic structures and optical constants were investigated. The band structures show an indirect band gap for this compound and the calculated band gaps expend with increasing pressure. Meanwhile, the optical properties including the dielectric spectra, absorption coefficient spectra, reflectivity, and the real part of the refractive index spectra in the low energy range have a blue shift. Given this, the optical properties of SrAl2O4 could be tuned by changing pressure to some degree, which is beneficial to the optical applications.


Materials ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 522
Author(s):  
Shubo Wei ◽  
Hanyu Liu

Generally, pressure is a useful tool to modify the behavior of physical properties of materials due to the change in distance between atoms or molecules in the lattice. Barium iodide (BaI2), as one of the simplest and most prototypical iodine compounds, has substantial high pressure investigation value. In this work, we explored the crystal structures of BaI2 at a wide pressure range of 0–200 GPa using a global structure search methodology. A thermodynamical structure with tetragonal I4/mmm symmetry of BaI2 was predicted to be stable at 17.1 GPa. Further electronic calculations indicated that I4/mmm BaI2 exhibits the metallic feature via an indirect band gap closure under moderate pressure. We also found that the superconductivity of BaI2 at 30 GPa is much lower than that of CsI at 180 GPa based on our electron–phonon coupling simulations. Our current simulations provide a step toward the further understanding of the high-pressure behavior of iodine compounds at extreme conditions.


Author(s):  
Bindu Rani ◽  
Aadil Wani ◽  
Utkir Sharopov ◽  
Kulwinder Kaur ◽  
Shobhna Dhiman

Half heusler compounds have gained attention due to their excellent properties and good thermal stability. In this paper, using first principle calculation and Boltzmann transport equation, we have investigated structural, electronic, mechanical and thermoelectric properties of PdXSn (X=Zr,Hf) half Heusler materials. These materials are indirect band gap semiconductors with band gap of 0.52 (0.44) for PdZrSn (PdHfSn). Calculations of elastic and phonon characteristics show that both materials are mechanically and dynamically stable. At 300K the magnitude of lattice thermal conductivity observed for PdZrSn is 15.16 W/mK and 9.53 W/mK for PdHfSn. The highest ZT value for PdZrSn and PdHfSn is 0.32 and 0.4 respectively.


2021 ◽  
Author(s):  
Xian-Hao Zhao ◽  
Tian-Yu Tang ◽  
Quan Xie ◽  
Li-Min Lu ◽  
Yan-Lin Tang

Abstract The current work has investigated the mechanical, electronic and optical properties of Pb-free vacancy-ordered double perovskites K2PdCl6 and K2PdBr6 by using first-principles calculations based on the framework of density functional theory (DFT). The calculated lattice constants of K2PdCl6 and K2PdBr6 are close to the experiments. It is determined by calculating the Goldschmidt’s tolerance factors and elastic constants of K2PdCl6 and K2PdBr6 that they can be stabilized into 3D cubic crystal structures. The calculated Poisson and Pugh’s ratios indicate that K2PdCl6 is a brittle material, while K2PdBr6 exhibits ductile behavior. Both K2PdCl6 and K2PdBr6 are indirect band gap semiconductors, which show suitable band gaps of 2.151 eV and 1.368 eV for optoelectronic devices, respectively. In addition, the optical properties of K2PdCl6 and K2PdBr6 in the photon energy range of 0−6 eV further reveal the application potential of these compounds in single-junction and tandem solar cells as well as other optoelectronic devices.


2021 ◽  
Author(s):  
P Gajjar ◽  
Dhara Raval ◽  
Sanjeev Gupta ◽  
Rajeev Ahuja

Abstract We studied the physical, electronic transport and optical properties of a unique pentagonal PdQ2 (Q= S, Se) monolayers. The dynamic stability of 2D - wrinkle like - PdQ2 is proven by positive phonon frequencies in the phonon dispersion curve. The optimized structural parameters of wrinkled pentagonal PdQ2 are in good agreement with the available experimental results. The ultimate tensile strength (UTHS) was calculated and found that, penta-PdS2 monolayer can withstand up to 16% (18%) strain along x (y) direction with 3.44 GPa (3.43 GPa). While, penta-PdSe2 monolayer can withstand up to 17% (19%) strain along x (y) dirrection with 3.46 GPa (3.40 GPa). It is found that, the penta-PdQ2 monolayers has the semiconducting behavior with indirect band gap of 0.94 and 1.26 eV for 2D-PdS2 and 2D-PdSe2, respectively. More interestingly, at room temperacture, the hole mobilty (electron mobility) obtained for 2D-PdS2 and PdSe2 are 67.43 (258.06) cm2 V-1 s-1 and 1518.81 (442.49) cm2 V-1 s-1, respectively. In addition, I-V characteristics of PdSe2 monolayer show strong negative differential conductance (NDC) region near the 3.57 V. The Shockly-Queisser (SQ) effeciency prameters of PdQ2 monolayers are also explored and the highest SQ efficeinciy obtained for PdS2 is 33.93% at -5% strain and for PdSe2 is 33.94% at -2% strain. The penta-PdQ2 exhibits high optical absorption intensity in the UV region, up to 4.04 × 105 (for PdS2) and 5.28 × 105 (for PdSe2), which is suitable for applications in optoelectronic devices. Thus, the ultrathin PdQ2 monolayers could be potential material for next-generation solar-cell applications and high performance nanodevices.


2021 ◽  
Vol 42 (12) ◽  
pp. 122002
Author(s):  
Xiaoshu Guo ◽  
Sandong Guo

Abstract A two-dimensional (2D) MA2Z4 family with and phases has been attracting tremendous interest, the MoSi2N4 and WSi2N4 of which have been successfully fabricated ( Science 369, 670 (2020)). Janus monolayers have been achieved in many 2D families, so it is interesting to construct a Janus monolayer from the MA2Z4 family. In this work, Janus MSiGeN4 (M = Zr and Hf) monolayers are predicted from -MA2Z4, which exhibit dynamic, mechanical and thermal stabilities. It is found that they are indirect band-gap semiconductors by using generalized gradient approximation (GGA) plus spin-orbit coupling (SOC). With biaxial strain from 0.90 to 1.10, the energy band gap shows a nonmonotonic behavior due to a change of conduction band minimum (CBM). A semiconductor to metal transition can be induced by both compressive and tensile strains, and the phase transformation point is about 0.96 for compressive strain and 1.10 for tensile strain. The tensile strain can change the positions of CBM and valence band maximum (VBM), and can also induce the weak Rashba-type spin splitting near CBM. For MSiGeN4 (M = Zr and Hf) monolayers, both an in-plane and out-of-plane piezoelectric response can be produced, when a uniaxial strain in the basal plane is applied, which reveals the potential as piezoelectric 2D materials. The high absorption coefficients in the visible light region suggest that MSiGeN4 (M = Zr and Hf) monolayers have potential photocatalytic applications. Our works provide an idea to achieve a Janus structure from the MA2Z4 family, and can hopefully inspire further research exploring Janus MA2Z4 monolayers.


Nanomaterials ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 3127
Author(s):  
Chen Chong ◽  
Hongxia Liu ◽  
Shulong Wang ◽  
Kun Yang

By adopting the first-principles plane wave pseudopotential method based on density functional theory, the electronic structure properties of single-layer MoS2 (molybdenum disulfide) crystals under biaxial strain are studied. The calculation results in this paper show that when a small strain is applied to a single-layer MoS2, its band structure changes from a direct band gap to an indirect band gap. As the strain increases, the energy band still maintains the characteristics of the indirect band gap, and the band gap shows a linear downward trend. Through further analysis of the density of states, sub-orbital density of states, thermodynamic parameters and Raman spectroscopy, it revealed the variation of single-layer MoS2 with strain. This provides a theoretical basis for realizing the strain regulation of MoS2.


2021 ◽  
Vol 6 (1) ◽  
Author(s):  
Z. L. Sun ◽  
A. F. Wang ◽  
H. M. Mu ◽  
H. H. Wang ◽  
Z. F. Wang ◽  
...  

AbstractRealizing applicably appreciated spintronic functionalities basing on the coupling between charge and spin degrees of freedom is still a challenge. For example, the anisotropic magnetoresistance (AMR) effect can be utilized to read out the information stored in magnetic structures. However, the application of AMR in antiferromagnet-based spintronics is usually hindered by the small AMR value. Here, we discover a colossal AMR with its value reaching 1.84 × 106% at 2 K, which stems from the field-induced metal-to-insulator transition (MIT), in a nearly Dirac material EuMnSb2. Density functional theory calculations identify a Dirac-like band around the Y point that depends strongly on the spin–orbit coupling and dominates the electrical transport. The indirect band gap at the Fermi level evolves with magnetic structure of Eu2+ moments, consequently giving rise to the field-induced MIT and the colossal AMR. Our results suggest that the antiferromagnetic topological materials can serve as a fertile ground for spintronics applications.


Author(s):  
Zhiyuan Sun ◽  
Jing Xu ◽  
Nsajigwa Mwankemwa ◽  
Wen-Xing Yang ◽  
Zao Yi ◽  
...  

Abstract Single-layer MoSi2N4, a high-quality two-dimensional material, has recently been fabricated by chemical vapor deposition. Motivated by this latest experimental work, herein, we apply first-principles calculations to investigate the electronic, optical, and photocatalytic properties of alkali-metals(Li, Na, and K)-adsorbed MoSi2N4 monolayer. The electronic structure analysis show that the pristine MoSi2N4 monolayer exhibits an indirect band gap (Eg=1.89 eV). By contrast, the band gaps of one Li-, Na- and K-adsorbed MoSi2N4 monolayers are 1.73, 1.61, and 1.75 eV, respectively. Moreover, the work function of the MoSi2N4 monolayer (4.80eV) is significantly reduced after the adsorption of alkali metal atoms. The work function of one Li-, Na- and K-adsorbed MoSi2N4 monolayers are 1.50, 1.43, and 2.03 eV, respectively. Then, the optical investigations indicate that alkali metal adsorption processes substantially increase the visible light absorption range and coefficient of the MoSi2N4 monolayer. Furthermore, based on redox potential variations after alkali-metals adsorbed, the Li-, and Na-adsorbed MoSi2N4 monolayer are more suitable for water splitting photocatalytic process, and the Li-adsorbed case shows the highest potential application for CO2 reduction. In conclusion, the alkali-metals-adsorbed MoSi2N4 monolayer exhibits promising applications as novel optoelectronic devices and photocatalytic materials due to the unique physical and chemical properties.


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