Energetic stability, oxidation states, and electronic structure of Bi-doped NaTaO3: a first-principles hybrid functional study

2016 ◽  
Vol 18 (2) ◽  
pp. 857-865 ◽  
Author(s):  
Paul H. Joo ◽  
Maziar Behtash ◽  
Kesong Yang
Keyword(s):  
Electronic Structure ◽  
First Principles ◽  
Relative Stability ◽  
Chemical Potential ◽  
Oxidation States ◽  
Functional Study ◽  
Hybrid Functional ◽  
Energetic Stability

Hybrid functional calculations (HSE) well predict the relative stability of Bi-doped NaTaO3 as a function of Na chemical potential.

First-principles hybrid functional study of the electronic structure and charge carrier mobility in perovskite CH 3 NH 3 SnI 3

2016 ◽  
Vol 25 (10) ◽  
pp. 107202 ◽  
Author(s):  
Li-Juan Wu ◽  
Yu-Qing Zhao ◽  
Chang-Wen Chen ◽  
Lin-Zhi Wang ◽  
Biao Liu ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Charge Carrier ◽  
First Principles ◽  
Carrier Mobility ◽  
Charge Carrier Mobility ◽  
Functional Study ◽  
Hybrid Functional

The Properties of a Na-Doped Twist Boundary in SrTiO3 from First Principles

2002 ◽  
Vol 751 ◽  
Author(s):  
Roope K. Astala ◽  
Paul D. Bristowe
Keyword(s):  
Electronic Structure ◽  
Grain Boundary ◽  
Plane Wave ◽  
First Principles ◽  
Driving Force ◽  
Chemical Potential ◽  
Twist Boundary ◽  
Atomic Displacements ◽  
Formation Energies ◽  
Oxygen Chemical Potential

ABSTRACTThe segregation of Nasr impurities to a Σ = 5 [001] twist boundary in SrTiO3 is studied using DFT-based plane-wave pseudopotential techniques. The formation energies of the impurities are calculated as a function of oxygen chemical potential and electron chemical potential. The results indicate a strong driving force for segregation to the boundary and that the Na impurities exhibit acceptor-like behaviour. The atomic displacements caused by the impurities are small both in the bulk and at the grain boundary. Based on the results a model is suggested in which Nasr segregation is driven by soft relaxation of the electronic structure.

Oxygen vacancy defects in tantalum pentoxide: a density functional study

2002 ◽  
Vol 745 ◽  
Author(s):  
R. Ramprasad ◽  
Michael Sadd ◽  
Doug Roberts ◽  
Tom Remmel ◽  
Mark Raymond ◽  
...  
Keyword(s):  
First Principles ◽  
Density Functional ◽  
Chemical Potential ◽  
Orthorhombic Phase ◽  
Functional Study ◽  
Vacancy Defects ◽  
Plane Type ◽  
Study Results ◽  
Wide Range ◽  
Very High

ABSTRACTFirst principles total energy calculations were performed in order to characterize O vacancy defects in Ta2O5. A simplified version of the crystalline orthorhombic phase of Ta2O5 was used in this study. Results indicate that O vacancies in Ta2O5 can be broadly classified based on their location in the lattice. One type of vacancies (occupying the “in-plane” sites) displays deep or mid gap occupied states, and shallow unoccupied states, while a second type (occupying “cap” sites) results in shallow occupied states. For a wide range of local Fermi level or chemical potential, the neutral and +2 charged states of the in-plane type vacancy and the +2 charge state of the cap type vacancy are found to be most stable. Migration energies of the two types of vacancies in the neutral and +2 charge states are markedly different, with the “cap” type of vacancies displaying very high barriers to migration (∼ 5 eV) compared to the “in-plane” type (∼ 0.5–1.0 eV).

Oxygen vacancy defects in tantalum pentoxide: a density functional study

2002 ◽  
Vol 747 ◽  
Author(s):  
R. Ramprasad ◽  
Michael Sadd ◽  
Doug Roberts ◽  
Tom Remmel ◽  
Mark Raymond ◽  
...  
Keyword(s):  
First Principles ◽  
Density Functional ◽  
Chemical Potential ◽  
Orthorhombic Phase ◽  
Functional Study ◽  
Vacancy Defects ◽  
Plane Type ◽  
Study Results ◽  
Wide Range ◽  
Very High

ABSTRACTFirst principles total energy calculations were performed in order to characterize O vacancy defects in Ta2O5. A simplified version of the crystalline orthorhombic phase of Ta2O5 was used in this study. Results indicate that O vacancies in Ta2O5 can be broadly classified based on their location in the lattice. One type of vacancies (occupying the “in-plane” sites) displays deep or mid gap occupied states, and shallow unoccupied states, while a second type (occupying “cap” sites) results in shallow occupied states. For a wide range of local Fermi level or chemical potential, the neutral and +2 charged states of the in-plane type vacancy and the +2 charge state of the cap type vacancy are found to be most stable. Migration energies of the two types of vacancies in the neutral and +2 charge states are markedly different, with the “cap” type of vacancies displaying very high barriers to migration (∼ 5 eV) compared to the “in-plane” type (∼ 0.5–1.0 eV).

A first principles study of the phonon anharmonicity, electronic structure and optical characteristics of LaAlO3

2018 ◽  
Vol 1 (1) ◽  
pp. 161-180 ◽  
Author(s):  
Bahaa Ilyas ◽  
Badal Elias
Keyword(s):  
Thermal Conductivity ◽  
Electronic Structure ◽  
Ab Initio ◽  
Conversion Efficiency ◽  
First Principles ◽  
Phonon Scattering ◽  
Phonon Dispersion ◽  
Optical Spectra ◽  
Hybrid Functional ◽  
The Way

The way elementary excitations work together with their couplings and interact as condensed matter systems is very important when designing optimum energy-conversion devices. We investigated the electronic structure of LaAlO3, and we show that the bandgap insulator of LaAlO3 obtained theoretically by the hybrid functional HSE06 is an indirect 5.649eV that show a very good agreement with experimental data. The lattice constant is obtained exactly as experiment. In thermos-electric materials, the concept of conversion-efficiency (heat to electricity) is improved instantly by suppressing the phonon quasi-particles propagations that are responsible for draft macroscopic thermal transport. The material presented here for thermo-electric conversion-efficiency of cubic perovskite LaAlO3, show that it has an ultralow thermal-conductivity, while the formalism to its strong phonon scattering interactions resides mostly unclear. From the bases of Ab-initio simulations, the 4-dimensional phonon-dispersion surfaces of the cubic perovskite LaAlO3, have been mapped and we found that the origins of the ionic potential an-harmonicity being responsible for the unique behaviour and properties of LaAlO3. It is investigated that these phonon scattering arise solely from the LaAlO3 unstable electronic-structure, with its orbital interactions resulting to lattice instability similar to the ferroelectric instabilities. Our results show a microscopic insight bonding electronic-structure and phonon an-harmonicity in LaAlO3, and provides some new picture the way interactions happen between phonon–electron and phonon–phonon this lead to understand the concept of ultralow thermal-conductivity. Ab-initio calculations was performed on cubic perovskite LaAlO3 to obtain the phonon density of states (DOS) from 50 K to 5000 K, we find that the anharmonic behaviour starts around temperature limits of 500 K. The computed optical spectra were obtained using both the Beth Slapter Equation BSE and compared with the perturbed method using HSE06, optical spectra show that the inter-band transition occur precisely from the O-valence bands to the La-conduction bands throughout the low energy area. The energy-loss spectrum, optical conductivity and reflectivity and the refractive index are computed from first principles by using HSE06 hybrid functional. The optical band gap of material shows about 6.21 eV, which agrees with some cited experimental measurements.

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