Open Access. Powered by Scholars. Published by Universities.^{®}

- Publication Year

- Publication

- Publication Type

- File Type

Articles **1** - **15** of ** 15**

## Full-Text Articles in Physics

Deformation, Lattice Instability, And Metallization During Solid-Solid Structural Transformations Under General Applied Stress Tensor: Example Of Si I -> Si Ii, Nikolai A. Zarkevich, Hao Chen, Valery I. Levitas, Duane D. Johnson

#### Deformation, Lattice Instability, And Metallization During Solid-Solid Structural Transformations Under General Applied Stress Tensor: Example Of Si I -> Si Ii, Nikolai A. Zarkevich, Hao Chen, Valery I. Levitas, Duane D. Johnson

*Materials Science and Engineering Publications*

Density functional theory (DFT) was employed to study the stress-strain behavior, elastic instabilities, and metallization during a solid-solid phase transformation (PT) between semiconducting Si I (cubic A4) and metallic Si II (tetragonal A5 structure) when subjected to a general stress tensor. With normal stresses (σ1, σ2, σ3) acting along ⟨110⟩, ⟨11¯0⟩, and ⟨001⟩, respectively, dictating the simulation cell, we determine combinations of 6 independent stresses that drive a lattice instability for the Si I→Si II PT, and a semiconductor-metal electronic transition. Metallization precedes the structural PT, hence, a stressed Si I can be a metal. Surprisingly, a stress-free ...

Growth And Characterization Of Baznga, Na Hyun Jo, Qisheng Lin, Udhara S. Kaluarachchi, William R. Meier, Soham Manni, Savannah S. Downing, Anna E. Böhmer, Tai Kong, Yang Sun, Valentin Taufour, Cai-Zhuang Wang, Kai-Ming Ho, Sergey L. Bud’Ko, Paul C. Canfield

#### Growth And Characterization Of Baznga, Na Hyun Jo, Qisheng Lin, Udhara S. Kaluarachchi, William R. Meier, Soham Manni, Savannah S. Downing, Anna E. Böhmer, Tai Kong, Yang Sun, Valentin Taufour, Cai-Zhuang Wang, Kai-Ming Ho, Sergey L. Bud’Ko, Paul C. Canfield

*Ames Laboratory Accepted Manuscripts*

We report the growth, structure and characterization of BaZnGa, identifying it as the sole known ternary compound in the Ba–Zn–Ga system. Single crystals of BaZnGa can be grown out of excess Ba–Zn and adopt a tI36 structure type. There are three unique Ba sites and three M = Zn/Ga sites. Using DFT calculations we can argue that whereas one of these three M sites is probably solely occupied by Ga, the other two M sites, most likely, have mixed Zn/Ga occupancy. Temperature-dependent resistivity and magnetization measurements suggest that BaZnGa is a poor metal with no electronic ...

Adsorption Of Dysprosium On The Graphite (0001) Surface: Nucleation And Growth At 300 K, Emma J. Kwolek, Huaping Lei, Ann Lii-Rosales, Mark Wallingford, Yinghui Zhou, Cai-Zhuang Wang, Michael C. Tringides, James W. Evans

#### Adsorption Of Dysprosium On The Graphite (0001) Surface: Nucleation And Growth At 300 K, Emma J. Kwolek, Huaping Lei, Ann Lii-Rosales, Mark Wallingford, Yinghui Zhou, Cai-Zhuang Wang, Michael C. Tringides, James W. Evans

*Physics and Astronomy Publications*

We have studied nucleation and growth of Dy islands on the basal plane of graphite at 300 K using scanning tunneling microscopy, density functional theory (DFT) in a form that includes van der Waals interactions, and analytic theory. The interaction of atomic Dy with graphite is strong, while the diffusion barrier is small. Experiment shows that at 300 K, the density of nucleated islands is close to the value predicted for homogeneous nucleation, using critical nucleus size of 1 and the DFT-derived diffusion barrier. Homogeneous nucleation is also supported by the monomodal shape of the island size distributions. Comparison with ...

Obtaining Mixed Ionic/Electronic Conductivity In Perovskite Oxides In A Reducing Environment: A Computational Prediction For Doped Srtio3, S. Suthirakun, Salai Ammal, G. Xiao, Fanglin Chen, Kevin Huang, Hans-Conrad Zur Loye, Andreas Heyden

#### Obtaining Mixed Ionic/Electronic Conductivity In Perovskite Oxides In A Reducing Environment: A Computational Prediction For Doped Srtio3, S. Suthirakun, Salai Ammal, G. Xiao, Fanglin Chen, Kevin Huang, Hans-Conrad Zur Loye, Andreas Heyden

*Salai C. Ammal*

No abstract provided.

Density Functional Theory Study On The Electronic Structure Of *N*- And *P*-Type Doped Srtio_{3} At Anodic Solid Oxide Fuel Cell Conditions, S. Suthirakun, Salai Ammal, G. Xiao, Fanglin Chen, Hans-Conrad Zur Loye, Andreas Heyden

#### Density Functional Theory Study On The Electronic Structure Of N- And P-Type Doped Srtio3 At Anodic Solid Oxide Fuel Cell Conditions, S. Suthirakun, Salai Ammal, G. Xiao, Fanglin Chen, Hans-Conrad Zur Loye, Andreas Heyden

*Salai C. Ammal*

The electronic conductivity and thermodynamic stability of mixed n-type and p-type doped SrTiO3 have been investigated at anodic solid oxide fuel cell (SOFC) conditions using density functional theory (DFT) calculations. In particular, constrained *ab initio* thermodynamic calculations have been performed to evaluate the phase stability and reducibility of various Nb- and Ga-doped SrTiO3 at synthesized and anodic SOFC conditions. The density of states (DOS) of these materials was analyzed to study the effects of n- and p-doping on the electronic conductivity. In agreement with experimental observations, we find that the transformation from 20% Nb-doped Sr-deficient SrTiO3 to a non-Sr-deficient phase ...

Magneto-Structural Transformations Via A Solid-State Nudged Elastic Band Method: Application To Iron Under Pressure, Nikolai A. Zarkevich, Duane D. Johnson

#### Magneto-Structural Transformations Via A Solid-State Nudged Elastic Band Method: Application To Iron Under Pressure, Nikolai A. Zarkevich, Duane D. Johnson

*Ames Laboratory Publications*

We extend the solid-state nudged elastic band method to handle a non-conserved order parameter, in particular, magnetization, that couples to volume and leads to many observed effects in magnetic systems. We apply this formalism to the well-studied magneto-volumecollapse during the pressure-induced transformation in iron—from ferromagnetic body-centered cubic (bcc) austenite to hexagonal close-packed (hcp) martensite. We find a bcc-hcp equilibrium coexistence pressure of 8.4 GPa, with the transition-state enthalpy of 156 meV/Fe at this pressure. A discontinuity in magnetization and coherent stress occurs at the transition state, which has a form of a cusp on the potential-energy surface ...

Nudged-Elastic Band Method With Two Climbing Images: Finding Transition States In Complex Energy Landscapes, Nikolai A. Zarkevich, Duane D. Johnson

#### Nudged-Elastic Band Method With Two Climbing Images: Finding Transition States In Complex Energy Landscapes, Nikolai A. Zarkevich, Duane D. Johnson

*Ames Laboratory Publications*

The nudged-elastic band (NEB) method is modified with concomitant two climbing images (C2-NEB) to find a transition state (TS) in complex energy landscapes, such as those with a serpentine minimal energy path (MEP). If a single climbing image (C1-NEB) successfully finds the TS, then C2-NEB finds it too. However, improved stability of C2-NEB makes it suitable for more complex cases, where C1-NEB misses the TS because the MEP and NEB directions near the saddle point are different. Generally, C2-NEB not only finds the TS, but also guarantees, by construction, that the climbing images approach it from the opposite sides along ...

Anomalous Magneto-Structural Behavior Of Mnbi Explained: A Path Towards An Improved Permanent Magnet, Nikolai A. Zarkevich, Linlin Wang, Duane D. Johnson

#### Anomalous Magneto-Structural Behavior Of Mnbi Explained: A Path Towards An Improved Permanent Magnet, Nikolai A. Zarkevich, Linlin Wang, Duane D. Johnson

*Ames Laboratory Publications*

Low-temperature MnBi (hexagonal NiAs phase) exhibits anomalies in the lattice constants (a, c) and bulk elastic modulus (B) below 100 K, spin reorientation and magnetic susceptibilitymaximum near 90 K, and, importantly for high-temperature magnetic applications, an increasingcoercivity (unique to MnBi) above 180 K. We calculate the total energy and magneto-anisotropyenergy (MAE) versus (a, c) using DFT+U methods. We reproduce and explain all the above anomalies. We predict that coercivity and MAE increase due to increasing a, suggesting means to improve MnBi permanent magnets.

Site-Preference And Valency For Rare-Earth Sites In (R-Ce)2fe14b Magnets, Aftab Alam, Mahmud Khan, R. William Mccallum, Duane D. Johnson

#### Site-Preference And Valency For Rare-Earth Sites In (R-Ce)2fe14b Magnets, Aftab Alam, Mahmud Khan, R. William Mccallum, Duane D. Johnson

*Ames Laboratory Publications*

Rare-earth (R) permanent magnets of R_{2}Fe_{14}B have technological importance due to their high energy products, and they have two R-sites (Wyckoff 4*f* and 4*g*, with four-fold multiplicity) that affect chemistry and valence. Designing magnetic behavior and stability via alloying is technologically relevant to reduce critical (expensive) R-content while retaining key properties;cerium, an abundant (cheap) R-element, offers this potential. We calculate magnetic propertiesand Ce site preference in ( R1−xCex) 2Fe14B [R = La,Nd] using density functional theory (DFT)methods—including a DFT + U scheme to treat localized 4*f*-electrons. Fe moments compare well ...

Chapter 14 – Evolutionary Algorithms Applied To Electronic-Structure Informatics: Accelerated Materials Design Using Data Discovery Vs. Data Searching, Duane D. Johnson

#### Chapter 14 – Evolutionary Algorithms Applied To Electronic-Structure Informatics: Accelerated Materials Design Using Data Discovery Vs. Data Searching, Duane D. Johnson

*Ames Laboratory Publications*

We exemplify and propose extending the use of genetic programs (GPs) – *a genetic algorithm (GA) that evolves computer programs via mechanisms similar to genetics and natural selection* – to symbolically regress key functional relationships between materials data, especially from electronic structure. GPs can extract *structure–property relations* or enable simulations across multiple scales of time and/or length. Uniquely, GP-based regression permits “data discovery” – finding relevant data and/or extracting correlations (data reduction/data mining) – in contrast to searching for what you know, or you think you know (intuition). First, catalysis-related materials correlations are discussed, where simple electronic-structure-based rules are revealed ...

Magnetostriction, Elasticity, And D03 Phase Stability In Fe–Ga And Fe–Ga–Ge Alloys, G. Petculescu, K. L. Ledet, Mianliang Huang, Thomas A. Lograsso, Y. N. Zhang, R. Q. Wu, M. Wun-Fogle, J. B. Restorff, A. E. Clark, K. B. Hathaway

#### Magnetostriction, Elasticity, And D03 Phase Stability In Fe–Ga And Fe–Ga–Ge Alloys, G. Petculescu, K. L. Ledet, Mianliang Huang, Thomas A. Lograsso, Y. N. Zhang, R. Q. Wu, M. Wun-Fogle, J. B. Restorff, A. E. Clark, K. B. Hathaway

*Ames Laboratory Conference Papers, Posters, and Presentations*

The contrast between the saturation tetragonal magnetostriction, λ^{γ,2} = (3/2)λ_{100}, of Fe_{1−x}Ga_{x} and Fe_{1−y}Ge_{y}, at compositions where both alloys exhibit D0_{3} cubic symmetry (*second peak* region), was investigated. This region corresponds to *x* = 28 at. % Ga and *y* = 18 at. % Ge or, in terms of *e*/*a* = 2 *x* + 3 *y* + 1, to an *e*/*a* value of ∼1.55 for each of the alloys. Single crystal, slow-cooled, ternary Fe_{1−x−y} Ga_{x}Ge_{y} alloys with *e*/*a* ∼1.55 and gradually increasing *y ...*

Density Functional Theory Study On The Electronic Structure Of *N*- And *P*-Type Doped Srtio_{3} At Anodic Solid Oxide Fuel Cell Conditions, S. Suthirakun, Salai Cheettu Ammal, G. Xiao, Fanglin Chen, Hans-Conrad Zur Loye, Andreas Heyden

#### Density Functional Theory Study On The Electronic Structure Of N- And P-Type Doped Srtio3 At Anodic Solid Oxide Fuel Cell Conditions, S. Suthirakun, Salai Cheettu Ammal, G. Xiao, Fanglin Chen, Hans-Conrad Zur Loye, Andreas Heyden

*Faculty Publications*

The electronic conductivity and thermodynamic stability of mixed n-type and p-type doped SrTiO3 have been investigated at anodic solid oxide fuel cell (SOFC) conditions using density functional theory (DFT) calculations. In particular, constrained *ab initio* thermodynamic calculations have been performed to evaluate the phase stability and reducibility of various Nb- and Ga-doped SrTiO3 at synthesized and anodic SOFC conditions. The density of states (DOS) of these materials was analyzed to study the effects of n- and p-doping on the electronic conductivity. In agreement with experimental observations, we find that the transformation from 20% Nb-doped Sr-deficient SrTiO3 to a non-Sr-deficient phase ...

Low-Temperature Adsorption Of H2s On Ag(111), Selena M. Russell, Da-Jiang Liu, Maki Kawai, Yousoo Kim, Patricia A. Thiel

#### Low-Temperature Adsorption Of H2s On Ag(111), Selena M. Russell, Da-Jiang Liu, Maki Kawai, Yousoo Kim, Patricia A. Thiel

*Chemistry Publications*

H_{2}S forms a rich variety of structures on Ag(111) at low temperature and submonolayer coverage. The molecules decorate step edges, exist as isolated entities on terraces, and aggregate into clusters and islands, under various conditions. One type of island exhibits a (×)R25.3° unit cell. Typically, molecules in the clusters and islands are separated by about 0.4 nm, the same as the S–S separation in crystalline H_{2}S. Density functional theory indicates that hydrogen-bonded clusters contain two types of molecules. One is very similar to an isolated adsorbed H_{2}S molecule, with both ...

Unbiased Density Functional Solutions Of Freezing In Binary Mixtures Of Hard Or Soft Spheres, M. Valera, R. F. Bielby, F. J. Pinksi, Duane D. Johnson

#### Unbiased Density Functional Solutions Of Freezing In Binary Mixtures Of Hard Or Soft Spheres, M. Valera, R. F. Bielby, F. J. Pinksi, Duane D. Johnson

*Duane D. Johnson*

various size ratios, σ2/σ1, using density functional theory. The Grand Potential is minimized using an unbiased, discrete, real-space mesh that does not constrain the shape of the density, and, in many cases, leads to solutions qualitatively different from those using Gaussians and plane-waves. Besides the usual face-centered-cubic solid-solution phase for σ2/σ1≈1.0, we find a sublattice-melt phase for σ2/σ1=0.85–0.5 (where the small-sphere density is nonlocalized and multi-peaked) and the NaCl phase for σ2/σ1=0.45–0.35 (when the small-sphere density again sharpens). For a range of size ratios of soft ...

The Slater–Pauling Curve: First Principles Calculations Of The Moments Of Fe1 − C Ni C And V1 − C Fe C, Duane D. Johnson, F. J. Pinski, J. B. Staunton

#### The Slater–Pauling Curve: First Principles Calculations Of The Moments Of Fe1 − C Ni C And V1 − C Fe C, Duane D. Johnson, F. J. Pinski, J. B. Staunton

*Duane D. Johnson*

We have performed calculations of the electronic structure of the random substitutional alloys Fe1−c Ni c and V1−c Fe c using the spin‐polarized, self‐consistent Korringa–Kohn–Rostoker coherent‐potential approximation (KKR‐CPA) method. This is a first principles method based on spin density functionaltheory and a local spin density approximation for the exchange and correlation functional. For fcc Fe1−c Ni c , a range of volumes were considered for 0.25