First-principles Studies of Phase Stability and the Neutral Atomic Vacancies in LiNbO3, NaNbO3 and KNbO3

2005 ◽  
Vol 902 ◽  
Author(s):  
Akio Shigemi ◽  
Takahiro Wada
Keyword(s):  
Enthalpy Of Formation ◽  
Density Functional ◽  
Formation Energy ◽  
Type Structure ◽  
Enthalpies Of Formation ◽  
Functional Formalism ◽  
Reducing Atmosphere ◽  
Perovskite Type Oxide ◽  
Formation Energies ◽  
Perovskite Type

AbstractWe overall evaluated the enthalpies of formation and the formation energies of neutral vacancies in ANbO3 (A = Li, Na, K) using a plane-wave pseudopotential method within a density functional formalism. The LiNbO3 phase with the LiNbO3-type structure was confirmed to have lower enthalpy of formation than that with perovskite- or ilmenite-type structure. The NaNbO3 (R3c) and KNbO3 (Bmm2 and R3m) phases with the lowest symmetry were found to have the lowest enthalpy of formation. The formation energy of a A vacancy was found to be the lowest under an oxidizing atmosphere and that of an O vacancy was found to be the lowest under a reducing atmosphere. The formation energy of a Nb vacancy was the highest under both oxygen-rich and -poor conditions. These results are in agreement with the empirical rule that B site defects in perovskite-type oxide do not exist.

Electronic structure and phase stability of In-free photovoltaic semiconductors, Cu2ZnSnSe4 and Cu2ZnSnS4 by first-principles calculation

2009 ◽  
Vol 1165 ◽  
Author(s):  
Tsuyoshi Maeda ◽  
Satoshi Nakamura ◽  
Takahiro Wada
Keyword(s):  
Electronic Structure ◽  
Plane Wave ◽  
Phase Stability ◽  
First Principles ◽  
Density Functional ◽  
Formation Enthalpy ◽  
First Principles Calculation ◽  
Enthalpies Of Formation ◽  
Functional Formalism ◽  
The Difference

AbstractWe have theoretically evaluated the phase stability and electronic structure of Cu2ZnSnSe4 (CZTSe) and Cu2ZnSnS4 (CZTS). The enthalpies of formation for kesterite, stannite and wurtz-stannite phases of CZTSe and CZTS were calculated using a plane-wave pseudopotential method within the density functional formalism. For CZTSe, the calculated formation enthalpy (ΔH) of the kesterite phase (−312.7 kJ/mol) is a little smaller than that of the stannite phase (−311.3 kJ/mol) and much smaller than that of the wurtz-stannite phase (−305.7 kJ/mol). For CZTS, the ΔH of the kesterite phase (−361.9 kJ/mol) is smaller than that of the stannite phase (−359.9 kJ/mol) and much smaller than that of the wurtz-stannite phase (−354.6 kJ/mol). The difference of ΔH between the kesterite and stannite phases for CZTS is greater than that for CZTSe. This indicates the kesterite phase is more stable than the stannite phase in CZTS compared with CZTSe. The valence band maximums (VBMs) of both the kesterite- and stannite-type CZTSe(CZTS) are antibonding orbitals of Cu 3d and Se 4p (S 3p). The conduction band minimums (CBMs) are antibonding orbitals of Sn 5s and Se 4p (S 3p). The Zn atom does not affect the VBM or the CBM in either CZTSe(CZTS). The theoretical band gap of the kesterite phase calculated with sX-LDA in both CZTSe and CZTS is a little wider than that of the wurtz-stannite phase and much wider than that of the stannite phase.

Phase stability and cohesive properties of Au–Sn intermetallics: A first-principles study

2008 ◽  
Vol 23 (5) ◽  
pp. 1398-1416 ◽  
Author(s):  
G. Ghosh
Keyword(s):  
Ground State ◽  
First Principles ◽  
Density Functional ◽  
Local Density ◽  
Metastable Phase ◽  
Equilibrium Diagram ◽  
Lattice Parameters ◽  
Enthalpies Of Formation ◽  
Cohesive Properties ◽  
Formation Energies

The total energies and cohesive properties of 29 Au–Sn intermetallics (stable, metastable, and virtual) are calculated from first-principles density-functional theory (DFT) employing ultrasoft pseudopotentials (USPP) and both local-density approximation (LDA) and generalized gradient approximation (GGA) for the exchange-correlation functional. Among the intermetallics considered, the ground-state structures are found to be AuSn, AuSn2, and AuSn4. Another phase Au5Sn, though present in the equilibrium diagram, lies slightly above the ground state convex hull. The formation energies of stable phases calculated using USPP–LDA and USPP–GGA are nearly the same. Except for AuSn, calorimetric data for enthalpies of formation show a good agreement with the calculated formation energies. Based on our first-principles results, it is argued that the structures of two metastable phases arecP52-type γ brass (isotypic with Al4Cu9) at Au–20.5 at.% Sn andhP1-type γ (isotypic with HgSn6–10) at Sn–8 at.% Au. For the intermetallics considered in this study, we provide optimized values of lattice parameters and Wyckoff positions. The experimental lattice parameters show a better agreement with those calculated using USPP–LDA than with USPP–GGA. The results presented here form the basis for creating a reliable thermodynamic database to facilitate calculations of stable and metastable phase diagrams of binary and multicomponent systems containing Au and Sn, relevant to electronic packaging and many other joining applications.

First-principles Calculations on the Zn1-xMgxO Window Layer Material for CIS Thin Film Solar Cells

2007 ◽  
Vol 1012 ◽  
Author(s):  
Tsuyoshi Maeda ◽  
Akio Shigemi ◽  
Takahiro Wada
Keyword(s):  
Solid Solution ◽  
Conduction Band ◽  
Density Functional ◽  
Window Layer ◽  
Enthalpies Of Formation ◽  
Wurtzite Phase ◽  
Functional Formalism ◽  
Rocksalt Phase ◽  
Solution Increase ◽  
Mg Content

AbstractWe have theoretically evaluated the phase stability and electronic structure of a Zn1-xMgxO solid solution. The enthalpies of formation for both the wurtzite and rocksalt phases of Zn1-xMgxO were calculated using a plane-wave pseudopotential method within the density functional formalism. For 0 < x < 0.5, the calculated enthalpies of formation (&[Delta]H) for the wurtzite phases were lower than those for the rocksalt phases. On the other hand, for x > 0.75, the &[Delta]H values for the wurtzite phase were larger than those for the rocksalt phases. This indicates that the wurtzite phase is more stable for a Zn1-xMgxO solid solution with 0 < x < 0.5, while the rocksalt phase is more stable for a solid solution with x > 0.75. The band gaps of a wurtzite Zn1-xMgxO solid solution increase with increasing Mg content. MgO substitution on Zn1-xMgxO largely affects the conduction band leaving the valence band nearly unchanged. The conduction band minimum (CBM) shifted to higher energy with increasing Mg content. These theoretical results qualitatively agree with the experimental results for Zn1-xMgxO thin films fabricated by RF magnetron co-sputtering.

Theoretical Studies of GaAs on Si

1989 ◽  
Vol 159 ◽  
Author(s):  
John E. Northrup
Keyword(s):  
Density Functional ◽  
Exchange Reactions ◽  
Functional Formalism ◽  
Bulk Gaas ◽  
Interface Dipole ◽  
Gaas On Si ◽  
Chemical Potentials ◽  
Metastable Structure ◽  
Si Films ◽  
Formation Energies

ABSTRACTThe energies of various two-dimensional GaAs on Si films have been calculated using the first principles pseudopotential method and density functional formalism. For GaAs on Si(111), the structures formed by adding a bilayer of GaAs to Si(111)1×1:As are shown to have positive formation energies, even after exchange reactions which eliminate the interface dipole are allowed. For GaAs on Si(100), the dependence of the formation energy of the films on the chemical potentials of the atomic constituents has been calculated. In the limit where μAs=μAs(bulk), and assuming the films have equilibrated with a bulk GaAs reservoir (μGa + μAs = μGaAs (bulk)), the lowest energy film is found to be the Si(100)2×1:As surface. In the opposite limit, μGa=μGa(bulk), the lowest energy film is the Si(100)2×1:(GaAs) surface. A new metastable structure obtained by adding 1/2 monolayer of Ga to Si(100)2×l:As has been studied.

Oxygen Vacancies in Amorphous HfO2 and SiO2

2008 ◽  
Vol 1073 ◽  
Author(s):  
Chioko Kaneta ◽  
Takahiro Yamasaki
Keyword(s):  
First Principles ◽  
Density Functional ◽  
Formation Energy ◽  
Oxygen Vacancies ◽  
Gate Dielectrics ◽  
Propagation Mechanism ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
The Difference ◽  
Formation Energies

ABSTRACTFormation energies and electronic properties of oxygen vacancies in amorphous HfO2 gate dielectrics are investigated by employing the first-principles method based on the density functional theory. We have found that the formation energy of neutral oxygen vacancy in amorphous HfO2 distributes from 4.7 to 6.1 eV, most of which is lower than the value for cubic HfO2, 6.0 eV. We also investigated the stabilities of the Vo pairs in various charged state and compared with those in amorphous SiO2. We found that Vo++ is stabilized in the vicinity of Vo in SiO2. In HfO2, however, this does not happen. This suggests the difference of defect propagation mechanism in HfO2 and SiO2.

Anisotropy of Piezoelectricity near Morphotropic Phase Boundary in Perovskite-Type Oxide Ferroelectrics

2002 ◽  
Vol 266 (1) ◽  
pp. 393-407
Author(s):  
Makoto Iwata ◽  
Hiroshi Orihara ◽  
Yoshihiro Ishibashi
Keyword(s):  
Phase Boundary ◽  
Morphotropic Phase Boundary ◽  
Perovskite Type Oxide ◽  
Perovskite Type

Optical Spectra, EPR, and Spin–Lattice Relaxation of Yb3+ Ions in Crystals Having Perovskite-Type Structure

1977 ◽  
Vol 81 (1) ◽  
pp. 287-293 ◽  
Author(s):  
A. A. Antipin ◽  
A. V. Vinokurov ◽  
M. P. Davydova ◽  
S. L. Korableva ◽  
A. L. Stolov ◽  
...  
Keyword(s):  
Lattice Relaxation ◽  
Optical Spectra ◽  
Type Structure ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Perovskite Type ◽  
Perovskite Type Structure
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