scholarly journals Rapid oxygen exchange between hematite and water vapor

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Zdenek Jakub ◽  
Matthias Meier ◽  
Florian Kraushofer ◽  
Jan Balajka ◽  
Jiri Pavelec ◽  
...  
Keyword(s):  
Water Vapor ◽  
Density Functional ◽  
Oxygen Exchange ◽  
Lattice Oxygen ◽  
Atomic Scale ◽  
Surrounding Water ◽  
Functional Theory ◽  
Research Fields ◽  
The Stability ◽  
The Cost

AbstractOxygen exchange at oxide/liquid and oxide/gas interfaces is important in technology and environmental studies, as it is closely linked to both catalytic activity and material degradation. The atomic-scale details are mostly unknown, however, and are often ascribed to poorly defined defects in the crystal lattice. Here we show that even thermodynamically stable, well-ordered surfaces can be surprisingly reactive. Specifically, we show that all the 3-fold coordinated lattice oxygen atoms on a defect-free single-crystalline “r-cut” ($$1\bar{1}02$$ 1 1 ¯ 02 ) surface of hematite (α-Fe2O3) are exchanged with oxygen from surrounding water vapor within minutes at temperatures below 70 °C, while the atomic-scale surface structure is unperturbed by the process. A similar behavior is observed after liquid-water exposure, but the experimental data clearly show most of the exchange happens during desorption of the final monolayer, not during immersion. Density functional theory computations show that the exchange can happen during on-surface diffusion, where the cost of the lattice oxygen extraction is compensated by the stability of an HO-HOH-OH complex. Such insights into lattice oxygen stability are highly relevant for many research fields ranging from catalysis and hydrogen production to geochemistry and paleoclimatology.

scholarly journals Substrate-Controlled Magnetism: Fe Nanowires on Vicinal Cu Surfaces

Nanomaterials ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 159 ◽  
Author(s):  
D. Hashemi ◽  
M. J. Waters ◽  
W. Hergert ◽  
J. Kieffer ◽  
V. S. Stepanyuk
Keyword(s):  
Density Functional ◽  
Magnetic Coupling ◽  
Atomic Scale ◽  
Magnetic Interactions ◽  
Critical Temperatures ◽  
Magnetic Exchange ◽  
Functional Theory ◽  
Novel Approach ◽  
The Stability ◽  
Exchange Parameters

Here we present a novel approach to controlling magnetic interactions between atomic-scale nanowires. Our ab initio calculations demonstrate the possibility to tune magnetic properties of Fe nanowires formed on vicinal Cu surfaces. Both intrawire and interwire magnetic exchange parameters are extracted from density functional theory (DFT) calculations. This study suggests that the effective interwire magnetic exchange parameters exhibit Ruderman–Kittel–Kasuya–Yosida-like (RKKY) oscillations as a function of Fe interwire separation. The choice of the vicinal Cu surface offers possibilities for controlling the magnetic coupling. Furthermore, an anisotropic Heisenberg model was used in Monte Carlo simulations to examine the stability of these magnetic configurations at finite temperatures. The predicted critical temperatures of the Fe nanowires on Cu(422) and Cu(533) surfaces are well above room temperature.

Phase Stability Study of the Shape Memory Alloy CuAl-X (X: Be, Zn, Ti, Ni, Ag and Au) by Ab Initio Calculations

2016 ◽  
Vol 879 ◽  
pp. 250-255
Author(s):  
Nassim Boudalia ◽  
Jean Marc Raulot ◽  
Etienne Patoor ◽  
Claude Esling
Keyword(s):  
Density Functional Theory ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
First Principles ◽  
Density Functional ◽  
Dft Method ◽  
Stability Study ◽  
Atomic Scale ◽  
Functional Theory ◽  
The Stability

Shape memory alloys (SMA) have been at the forefront of research in recent years. They have been used for a wide variety of applications in various fields. This work presents a brief study at the atomic scale of Cu-Al based Shape Memory Alloys. Using first-principles Density Functional Theory (DFT) method, the stability of different austenitic and martensitic phases of Cu3Al, the effect of intrinsic vacancies, the doping effect by an element X (X = Be, Zn, Ti, Ni, Ag and Au) have been studied.

Effects of Alloying Elements on the Stability of ω-Fe Phase in Steel: A Density Functional Theory Study

2021 ◽  
Vol 1016 ◽  
pp. 1246-1251
Author(s):  
S. Assa Aravindh ◽  
Sakari Pallaspuro ◽  
Wei Cao ◽  
Mahesh Somani ◽  
Matti Alatalo ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Cohesive Energy ◽  
Density Functional ◽  
Magnetic Moments ◽  
Ferromagnetic State ◽  
Atomic Scale ◽  
Alloying Elements ◽  
Density Functional Theory Study ◽  
Functional Theory ◽  
The Stability

Recent advances in transmission electron microscopy (TEM) in respect of structural characterization down to atomic scale have enabled confirmation of stabilization of long ignored hexagonal omega (ω) phase in steel. The presence of ω phase is suggested to increase the strength of steel, and one of the factors concerning its stabilization is enrichment caused by the presence of certain solute atoms in the nanometer sized areas. Here, we report a density functional theory study conducted on a (3×3×2) ω –Fe supercell by introducing alloying elements in such a way that at a particular instant, either interstitial or substitutional C co-exist with any one of the elements Mn, Cr, Al, Si, and Co in substitutional position. From total energy calculations, we show that the cohesive energy of ω-Fe supercell increases in general, and the most stable combinations in the decreasing order of stability are Csub-Cr > Csub-Co > Csub-Si. Even though the ferromagnetic state is more stable when compared to non-magnetic and antiferromagnetic configurations, the total magnetism of the supercell decreases as some of the atoms acquire negative magnetic moments. The density of states analysis shows that the d-band width of Fe decreases in presence of alloying elements, and this can lead to increased cohesive energy. Our results elucidate that the presence of minor alloying elements can be a factor in stabilizing the metastable ω-phase in steel.

Thermodynamic Stability of Hexagonal and Rhombohedral Bn at Cvd Conditions from Van der Waals Corrected First Principles Calculations

2019 ◽  
Author(s):  
Henrik Pedersen ◽  
Björn Alling ◽  
Hans Högberg ◽  
Annop Ektarawong
Keyword(s):  
Thin Films ◽  
Thermodynamic Stability ◽  
First Principles ◽  
Thermal Equilibrium ◽  
Density Functional ◽  
Van Der Waals ◽  
Chemical Vapor ◽  
First Principles Calculations ◽  
Functional Theory ◽  
The Stability

Thin films of boron nitride (BN), particularly the sp<sup>2</sup>-hybridized polytypes hexagonal BN (h-BN) and rhombohedral BN (r-BN) are interesting for several electronic applications given band gaps in the UV. They are typically deposited close to thermal equilibrium by chemical vapor deposition (CVD) at temperatures and pressures in the regions 1400-1800 K and 1000-10000 Pa, respectively. In this letter, we use van der Waals corrected density functional theory and thermodynamic stability calculations to determine the stability of r-BN and compare it to that of h-BN as well as to cubic BN and wurtzitic BN. We find that r-BN is the stable sp<sup>2</sup>-hybridized phase at CVD conditions, while h-BN is metastable. Thus, our calculations suggest that thin films of h-BN must be deposited far from thermal equilibrium.

Site preference and atomic ordering in the ternary Rh5Ga2As: first-principles calculations

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Nilanjan Roy ◽  
Sucharita Giri ◽  
Harshit ◽  
Partha P. Jana
Keyword(s):  
Total Energy ◽  
First Principles ◽  
Density Functional ◽  
Structure Type ◽  
Site Preference ◽  
X Ray Diffraction ◽  
Atomic Ordering ◽  
Functional Theory ◽  
The Stability ◽  
Bonding Characteristics

Abstract The site preference and atomic ordering of the ternary Rh5Ga2As have been investigated using first-principles density functional theory (DFT). An interesting atomic ordering of two neighboring elements Ga and As reported in the structure of Rh5Ga2As by X-ray diffraction data only is confirmed by first-principles total-energy calculations. The previously reported experimental model with Ga/As ordering is indeed the most stable in the structure of Rh5Ga2As. The calculation detected that there is an obvious trend concerning the influence of the heteroatomic Rh–Ga/As contacts on the calculated total energy. Interestingly, the orderly distribution of As and Ga that is found in the binary GaAs (Zinc-blende structure type), retained to ternary Rh5Ga2As. The density of states (DOS) and Crystal Orbital Hamiltonian Population (COHP) are calculated to enlighten the stability and bonding characteristics in the structure of Rh5Ga2As. The bonding analysis also confirms that Rh–Ga/As short contacts are the major driving force towards the overall stability of the compound.

scholarly journals The stability and electronic and photocatalytic properties of the ZnWO4 (010) surface determined from first-principles and thermodynamic calculations

RSC Advances ◽  
2021 ◽  
Vol 11 (38) ◽  
pp. 23477-23490
Author(s):  
Yonggang Wu ◽  
Jihua Zhang ◽  
Bingwei Long ◽  
Hong Zhang
Keyword(s):  
Phase Diagram ◽  
Density Functional Theory ◽  
First Principles ◽  
Density Functional ◽  
Thermodynamic Calculations ◽  
Photocatalytic Properties ◽  
Thermodynamic Approach ◽  
Functional Theory ◽  
Stability Phase Diagram ◽  
The Stability

The ZnWO4 (010) surface termination stability is studied using a density functional theory-based thermodynamic approach. The stability phase diagram shows that O-Zn, DL-W, and DL-Zn terminations of ZnWO4 (010) can be stabilized.

A DENSITY FUNCTIONAL STUDY OF THE STRUCTURE OF SILANE COUPLING AGENT 3–AMINOPROPYLTRIETHOXYSILANE

2005 ◽  
Vol 04 (01) ◽  
pp. 117-126
Author(s):  
N. L. MA ◽  
P. WU
Keyword(s):  
Coupling Agent ◽  
Density Functional ◽  
Solution Structure ◽  
Silane Coupling Agent ◽  
Industrial Applications ◽  
Functional Study ◽  
Stable Form ◽  
Functional Theory ◽  
Silane Coupling ◽  
The Stability

Using density functional theory, we predicted the solution structure of the hydrolyzed 3–aminopropyltriethoxysilane (h–APS), which is a silane coupling agent commonly used in many industrial applications. We have located five stable minima on the potential energy surface of h–APS in which four of them are "neutral", and the remaining one is zwitterionic (dipolar) in nature. Our calculations suggested that the stability of the most stable form of h–APS in water (denoted as II_N) arose from strong intramolecular OH ⋯ N hydrogen bond. The least stable form is the zwitterionic form (I_ZW), which is estimated to be over 90 kJ mol -1 less stable than II_N. The factors governing the relative stabilities of different forms are discussed.

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