The Effect of Lanthanum Doping and Oxygen Vacancy on Perovskite, Pyrochlore Oxide and Lanthanide Titanates: A First Principle Study

MRS Advances ◽  
2019 ◽  
Vol 4 (20) ◽  
pp. 1167-1175
Author(s):  
Amar Deep Pathak ◽  
Foram Thakkar ◽  
Suchismita Sanyal ◽  
Arian Nijmeijer ◽  
Hans Geerlings
Keyword(s):  
Bulk Modulus ◽  
Band Gap ◽  
Density Functional ◽  
Electronic Conductivity ◽  
Formation Enthalpy ◽  
Wide Band ◽  
Layered Perovskite ◽  
Lanthanum Doping ◽  
Reducing Environment ◽  
La Substitution

AbstractThe effects of La-substitution into SrTiO3 (STO) perovskite oxides on their phase structure, formation enthalpy and electrical conductivity have been investigated. La substitution in STO has been reported to show a significant enhancement in electronic conductivity in a wide-band-gap layered perovskite compound STO. Mixture of Lanthanum and Titanium oxide may lead to various phases including La2/3TiO3, La2Ti2O7 and La2TiO5. In this work, more than 50 structural models have been constructed by considering ionic state substituents, distance between substituents and their concentrations. We investigated the formation enthalpy, elastic properties and band gap by density functional theory (DFT) calculations. We have also investigated the effect of reducing environment on La2/3TiO3. The computed bulk modulus (∼2.4 % deviation) and band gap (∼12% deviation) of STO are in good agreement with the literature. Our results indicate that La substitution into STO could significantly reduce the band gap. Reduction in band gap is maximum when the substituents is present at low concentrations. Internal position of La substituents in STO affects the band gap marginally while energy remains almost same. Formation enthalpy of La2/3TiO3 from LaTiO3 is around 2 eV. La2/3TiO3 acts as band insulator (band gap = 2.8 eV). In reducing environment, the band gap of La2/3TiO3 significantly reduces. Sr substitution in La2/3TiO3 lower the band gap and formation enthalpy. La2Ti2O7 and La2TiO5 have higher band gap and lower bulk modulus than STO. Sr substitution is not feasible in La2Ti2O7 and La2TiO5.

scholarly journals Novel III-V Nitride Polymorphs in the P42/mnm and Pbca Phases

Materials ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 3743 ◽  
Author(s):  
Qingyang Fan ◽  
Xin Ai ◽  
Junni Zhou ◽  
Xinhai Yu ◽  
Wei Zhang ◽  
...  
Keyword(s):  
Shear Modulus ◽  
Bulk Modulus ◽  
Band Gap ◽  
Density Functional ◽  
Mechanical Stability ◽  
Elastic Anisotropy ◽  
Wide Band ◽  
Light Emitting ◽  
Ultraviolet Detectors ◽  
Direct Band

In this work, the elastic anisotropy, mechanical stability, and electronic properties for P42/mnm XN (XN = BN, AlN, GaN, and InN) and Pbca XN are researched based on density functional theory. Here, the XN in the P42/mnm and Pbca phases have a mechanic stability and dynamic stability. Compared with the Pnma phase and Pm-3n phase, the P42/mnm and Pbca phases have greater values of bulk modulus and shear modulus. The ratio of the bulk modulus (B), shear modulus (G), and Poisson’s ratio (v) of XN in the P42/mnm and Pbca phases are smaller than those for Pnma XN and Pm-3n XN, and larger than those for c-XN, indicating that Pnma XN and Pm-3n XN are more ductile than P42/mnm XN and Pbca XN, and that c-XN is more brittle than P42/mnm XN and Pbca XN. In addition, in the Pbca phases, XN can be considered a semiconductor material, while in the P42/mnm phase, GaN and InN have direct band-gap, and BN and AlN are indirect wide band gap materials. The novel III-V nitride polymorphs in the P42/mnm and Pbca phases may have great potential for application in visible light detectors, ultraviolet detectors, infrared detectors, and light-emitting diodes.

scholarly journals First-principles study of solid methane at high pressure

BIBECHANA ◽  
2014 ◽  
Vol 12 ◽  
pp. 70-79 ◽  
Author(s):  
Nurapati Pantha ◽  
Jagaran Acharya ◽  
Narayan Prasad Adhikari
Keyword(s):  
High Pressure ◽  
Band Gap ◽  
First Principles ◽  
Density Functional ◽  
Wide Band ◽  
Orthorhombic Structure ◽  
Generalized Gradient ◽  
Reported Data ◽  
Quantum Espresso ◽  
Solid Methane

We study the structural and electronic properties of solid methane of space group P212121 at high pressure. The density-functional theory (DFT) based first-principles calculations within the Generalized Gradient Approximations (GGA) have been performed by using Quantum Espresso package. Our findings show that the solid methane in orthorhombic structure compresses fast at the first, and then slowly as a function of elevated hydrostatic pressure. The pressure-volume diagram agrees with the available previously reported data up to pressure of around 200 GPa. In orthorhombic structure, solid methane is a wide band gap insulator at low pressures (tens of GPa). The band gap decreases with increase in the pressure. At high pressure (around 900 GPa), the band gap decreases to semi-conductor range (1.78 eV). Our results reveal that methane to be metallic above the pressure coverage of the present study which is consistent to the interior of the giant planets. The band gap as a function of pressure (from the present work) agrees well with the previously reported data. DOI: http://dx.doi.org/10.3126/bibechana.v12i0.11779BIBECHANA 12 (2015) 70-79

scholarly journals Ground State Properties of the Wide Band Gap Semiconductor Beryllium Sulfide (BeS)

Materials ◽  
2021 ◽  
Vol 14 (20) ◽  
pp. 6128
Author(s):  
Blaise A. Ayirizia ◽  
Janee’ S. Brumfield ◽  
Yuriy Malozovsky ◽  
Diola Bagayoko
Keyword(s):  
Band Gap ◽  
Lattice Constant ◽  
Ground State ◽  
Density Functional ◽  
Local Density ◽  
Wide Band ◽  
Electronic Energy ◽  
Computational Method ◽  
Energy Bands ◽  
Ground State Properties

We report the results from self-consistent calculations of electronic, transport, and bulk properties of beryllium sulfide (BeS) in the zinc-blende phase, and employed an ab-initio local density approximation (LDA) potential and the linear combination of atomic orbitals (LCAO). We obtained the ground state properties of zb-BeS with the Bagayoko, Zhao, and Williams (BZW) computational method, as enhanced by Ekuma and Franklin (BZW-EF). Our findings include the electronic energy bands, the total (DOS) and partial (pDOS) densities of states, electron and hole effective masses, the equilibrium lattice constant, and the bulk modulus. The calculated band structure clearly shows that zb-BeS has an indirect energy band gap of 5.436 eV, from Γ to a point between Γ and X, for an experimental lattice constant of 4.863 Å. This is in excellent agreement with the experiment, unlike the findings of more than 15 previous density functional theory (DFT) calculations that did not perform the generalized minimization of the energy functional, required by the second DFT theorem, which is inherent to the implementation of our BZW-EF method.

First-Principle Study of the Structural, Electronic, and Optical Properties of Cubic Cesium Lead Halide Perovskites for Photovoltaic System

2020 ◽  
Vol 4 (2) ◽  
pp. 1-16
Author(s):  
Muhammad Waqas
Keyword(s):  
Optical Properties ◽  
Band Gap ◽  
Density Functional ◽  
Covalent Bond ◽  
Wide Band ◽  
Photovoltaic System ◽  
Full Potential ◽  
Potential Applications ◽  
Halide Perovskites ◽  
Lead Halide

Lead halide perovskites have attracted considerable attention as optoelectronic materials because these materials have high photovoltaic conversion efficiency. The current study is based on Density Functional Theory (DFT). This theory was used to calculate the structural, optical, and electronic properties of the lead halide perovskites CsPbX3 (X = Chlorine (Cl), Bromine (Br), Iodine (I)) compounds . In order to calculate the above mentioned properties of cubic perovskites CsPbX3 (X = Cl, Br, I), Full Potential Linear Augmented Plane Wave (FP-LAPW) method was implemented in conjunction with DFT utilizing LDA, GGA-PBE and mBJ approximations. A good agreement was found between experimentally measured values and theoretically calculated lattice constants. These compounds have a direct and wide band gap located at the point of R-symmetry, while the band gap decreases from ‘Cl’ to ‘I’ down the group. The densities of electrons revealed a strong ionic bond between Cs and halides and a strong covalent bond between ‘Pb’ and (Cl, Br, and I). The dielectric functions (reflectivity, refractive indices, absorption coefficients), optical conductivities (real and imaginary part) and other optical properties indicated that these compounds have novel energy harvester applications. The modeling of these perovskite compounds shows that they have high absorption power and direct band gaps in visible ultraviolet range and it also shows that these compounds have potential applications in solar cells.

Doping Limitation Due to Self-compensation by Native Defects in In-doped Rocksalt CdxZn1-xO

2021 ◽  
Author(s):  
Chun Yuen HO ◽  
Chia Hsiang Li ◽  
Chao Ping Liu ◽  
Zhi-Quan Huang ◽  
Feng-Chuan Chuang ◽  
...  
Keyword(s):  
Dft Calculations ◽  
Band Gap ◽  
Electron Mobility ◽  
Density Functional ◽  
Defect Formation ◽  
Wide Band ◽  
High Electron ◽  
Transparent Conductor ◽  
Full Spectrum ◽  
Native Defects

Abstract CdO-ZnO alloys (CdxZn1-xO) exhibit a transformation from the wurtzite (WZ) to the rocksalt (RS) phase at a CdO composition of ~70% with a drastic change in the band gap and electrical properties. RS-CdxZn1-xO alloys (x>0.7) are particularly interesting for transparent conductor applications due to their wide band gap and high electron mobility. In this work, we synthesized RS-CdxZn1-xO alloys doped with different concentrations of In dopants and evaluated their electrical and optical properties. Experimental results are analyzed in terms of the amphoteric native defect model and compared directly to defect formation energies obtained by hybrid density functional theory (DFT) calculations. A saturation in electron concentration of ~7x1020cm-3 accompanied by a rapid drop in electron mobility is observed for the RS-CdxZn1-xO films with 0.7≤x<1 when the In dopant concentration [In] is larger than 3%. Hybrid DFT calculations confirm that the formation energy of metal vacancy acceptor defects is significantly lower in RS-CdxZn1-xO than in CdO, and hence limits the free carrier concentration. Mobility calculations reveal that due to the strong compensation by native defects, RS-CdxZn1-xO alloys exhibit a compensation ratio of >0.7 for films with x<0.8. As a consequence of the compensation by native defects, in heavily doped RS-CdxZn1-xO carrier-induced band filling effect is limited. Furthermore, the much lower mobility of the RS-CdxZn1-xO alloys also results in a higher resistivity and reduced transmittance in the near infra-red region (λ>1100 nm), making the material not suitable as transparent conductors for full spectrum photovoltaics.

Theoretical Analysis of the DOS and Band Structural Properties of Ti1-XSnxO2 Solid Solutions

2012 ◽  
Vol 465 ◽  
pp. 33-36
Author(s):  
Zhi Dong Lin ◽  
Wen Long Song ◽  
Ju Cheng Zheng
Keyword(s):  
Band Gap ◽  
Solid Solutions ◽  
Density Functional ◽  
Wide Band ◽  
Low Energy ◽  
Low Density ◽  
First Principle ◽  
Wide Band Gap ◽  
Functional Theory ◽  
First Principle Calculations

The band structure and density of states (DOS) of Ti1-xSnxO2 solid solutions with x=0, 1/8, 1/4, 1/2 and 1 were investigated by means of the first-principle calculations based on density functional theory. The result indicated that band gap and Fermi level of TiO2-SnO2 vary continuously from those of pure TiO2 to those of Sn content increasing. In addition, the DOS moves towards low energy and the bang gap is broadened with growing value of x. The wide band gap and the low density of the states in the conduction band result in the enhancement of photoactivity in Ti1-xSnxO2.

First Principles Calculations of Electronic and Optical Properties of Al1-xLaxN

2011 ◽  
Vol 393-395 ◽  
pp. 110-113
Author(s):  
Chang Peng Chen ◽  
Mei Lan Qi
Keyword(s):  
Optical Properties ◽  
Band Gap ◽  
Density Functional ◽  
Density Functional Method ◽  
High Energy ◽  
Functional Method ◽  
Absorption Region ◽  
Additional Absorption ◽  
Calculation Results ◽  
La Substitution

Based on the density functional method, the electronic structures and the optical properties for Al1-xLaxN(x=0, 0.0625, 0.125, 0.1875) are comparatively investigated in detail. The calculation results indicate that La substitution of the Al sites induces effective reduction of the band gap of AlN, and the band gap being continuously reduced when increasing La doping level. With the increase of La concentration, both the imaginary part of dielectric function and the absorption spectrum show red-shift corresponding to the change of band gaps. Moreover, additional absorption peaks are observed above the absorption edge in the high-energy range which widens the absorption region.

BULK MODULUS CALCULATIONS FOR GROUP-IV CARBIDES AND GROUP-III NITRIDES

2004 ◽  
Vol 18 (24) ◽  
pp. 1247-1254 ◽  
Author(s):  
A. MAHMOOD ◽  
L. E. SANSORES ◽  
J. HEIRAS
Keyword(s):  
Bulk Modulus ◽  
Density Functional ◽  
Theoretical Calculations ◽  
Wide Band ◽  
Group Iii Nitrides ◽  
Group Iv ◽  
Hard Coatings ◽  
Generalized Gradient ◽  
Group Iii ◽  
Quantum Mechanical Method

Wide band gap semiconductors such as group-IV carbides ( SiC , GeC ) and group-III nitrides ( AlN , GaN and BN ) are known to be important materials for novel semiconductor applications. They also have interesting mechanical properties such as having a particularly high value for their bulk modulus and are therefore potential candidates for hard coatings. In this paper we report the theoretical calculations for the bulk modulus for zincblende and wurzite polytypes of these materials. The Density Functional and Total-energy Pseudopotential Techniques in the Generalized Gradient approximation, an ab initio quantum mechanical method, is used to obtain the theoretical structure, from which equilibrium lattice parameters and volume of the cell versus pressure may be extracted. The Murnaghan's equation of state is then used to calculate bulk modulus under elastic deformation, which is related to the hardness of a material under certain conditions. The results for bulk modulus are compared with other theoretical and experimental values reported in the literature.

STRUCTURAL, ELECTRONIC, THERMODYNAMIC AND THERMAL PROPERTIES OF ZINC-BLENDE InP, InAs AND THEIR InAsx P1-x TERNARY ALLOYS VIA FIRST PRINCIPLES CALCULATIONS

2013 ◽  
Vol 27 (27) ◽  
pp. 1350166 ◽  
Author(s):  
O. NEMIRI ◽  
S. GHEMID ◽  
Z. CHOUAHDA ◽  
H. MERADJI ◽  
F. EL HAJ HASSAN
Keyword(s):  
Thermal Properties ◽  
Bulk Modulus ◽  
Band Gap ◽  
Lattice Constant ◽  
First Principles ◽  
Density Functional ◽  
Experimental Studies ◽  
Ternary Alloys ◽  
Full Potential ◽  
First Principles Calculations

First-principles calculations are performed to study the structural, electronic, thermodynamic and thermal properties of the InP and InAs bulk materials and InAs x P 1-x ternary alloys using the full potential-linearized augmented plane wave method (FP-LAPW) within the density functional theory (DFT). The dependence of the lattice constant, bulk modulus, band gap, Debye temperature, heat capacity and mixing entropy on the composition x was analyzed. The lattice constant for InAs x P 1-x alloys exhibits a marginal deviation from the Vegard's law. A large deviation of the bulk modulus from linear concentration dependence (LCD) was observed for our alloys. We found that the composition dependence of the energy band gap is almost linear by using the mBJ and EV-GGA approximations. The microscopic origins of the gap bowing were explained and detailed by using the approach of Zunger and co-workers. Furthermore, the calculated phase diagram shows a miscibility gap for these alloys with a high critical temperature. Thermal effects on some macroscopic properties of InAs x P 1-x alloys are predicted using the quasi-harmonic Debye model, in which the phononic effects are considered. This is the first quantitative theoretical prediction of the thermal properties of the InAs x P 1-x alloys, and we still expect the confirmation of experimental studies.

scholarly journals Ab Initio Study of MgTe Self-Interstitial (Mgi and Tei): A Wide Band Gap Semiconductor

2017 ◽  
Vol 16 ◽  
pp. 47-51
Author(s):  
Emmanuel Igumbor ◽  
Ezekiel Omotoso ◽  
Walter Ernst Meyer
Keyword(s):  
Band Gap ◽  
Density Functional ◽  
Defect Formation ◽  
Local Density ◽  
Wide Band ◽  
Shallow Donor ◽  
Generalized Gradient ◽  
Wide Band Gap ◽  
Functional Theory ◽  
Formation Energies

We present results of defect formation energies and charge state thermodynamic transition levels of Mg and Te interstitials in MgTe wurzite structure. We use the generalized gradient approximation and local density approximation functionals in the framework of density functional theory for all calculations. The formation energies of the Mg and Te interstitials in MgTe for both the tetrahedral and hexagonal configurations were obtained. The Mg and Te interstitials in MgTe depending on the functional, introduced transition state levels that are either donor or acceptor within the band gap of the MgTe. The Te interstitial exhibit charge states controlled metastability, negative-U and DX centre properties. The Mg interstitial acts as deep or shallow donor and there is no evidence of acceptor levels found for the Mg interstitial.

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