scholarly journals Investigative properties of CeO2 doped with niobium: A combined characterization and DFT studies

2021 ◽  
Vol 11 (1) ◽  
pp. 191-203
Author(s):  
Toyin Shittu ◽  
Mohammednoor Altarawneh
Keyword(s):  
Density Functional ◽  
Surface Acidity ◽  
High Surface ◽  
Thermal Characteristics ◽  
Atomic Charge ◽  
Particle Growth ◽  
Structural Features ◽  
Lattice Parameter ◽  
First Principle Calculation ◽  
Nb Doping

Abstract Catalytic capacity of ceria mainly stems from a facile switch in the Ce oxidation states from +4 to +4 − x. While various experimental and computational studies pinpoint the reduction chemistry of Ce atom through the creation of oxygen vacancies, the analogous process when ceria surface is decorated with cations remains poorly understood. Where such results are available, a synergy between experimental and first principle calculation is scarce. Niobium materials are evolving and their use in catalysis is being widely investigated due to their high surface acidity and thermal and chemical stability. This study aims to report structural and electronic properties of various configurations of mixed Ce–Nb oxides and elaborates on factors that underpin potential catalytic improvements. Evaluations of the samples through X-ray diffraction (XRD), Fourier transform infrared (FTIR), N2-adsorption–desorption, scanning electron microscope (SEM), energy dispersive spectroscope (EDS), and thermogravimetric (TGA) analyses are examined and discussed. First principles density functional theory (DFT) calculations provide structural features of the Ce–Nb solutions at low concentration of Nb via computing atomic charge distribution. Contraction in the lattice parameter after Nb doping was confirmed with both XRD and DFT results. SEM analysis reveals particle growth at the loading of 50 wt%. FTIR results established the Ce–Nb–O bond at 1,100 cm−1 and the TGA analysis confirms the thermal stability of Nb-doped ceria. Tetrahedral O atoms demonstrate an increase in electronegativity and this in turn facilitates catalytic propensity of the material because the O atoms will exhibit higher affinity for adsorbed reactants. Cerium oxide (CeO2) after Nb doping displays a noticeable band gap narrowing, confirming the possible improvement in the catalytic behavior. The 4d states of the Niobium pentoxide (Nb2O5) is found to fill up the 4f states of CeO2 around the Fermi energy level promoting electrons excitation in the CeO2. Reported electronic, structural, and thermal characteristics herein indicate promising catalytic applications of niobium-promoted ceria.

scholarly journals First Principle Study on Atomic Scale Structures of Cathode in Aluminium-ion Battery Using Various van der Waals Corrections

2020 ◽  
Vol 213 ◽  
pp. 01023
Author(s):  
Kaihao Geng ◽  
Haining Cao ◽  
Meng-Chang Lin
Keyword(s):  
Density Functional ◽  
Van Der Waals ◽  
Structural Features ◽  
Atomic Scale ◽  
First Principle ◽  
Functional Theory ◽  
Principle Calculation ◽  
First Principle Calculation ◽  
Aluminium Ion ◽  
Scale Structures

There is still controversy on the atomistic configuration of aluminium-ion batteries (AIB) cathode when using first principle calculation based on density functional theory (DFT). We examined the relevant cathodic structures of Al/graphite battery by employing several van der Waals (vdW) corrections. Among them, DFT-TS method was determined to be a better dispersion correction in correctly rendering structural features already found through experiment investigations. The systematic comparison paved the way to the choice of vdW parameters in first principle calculation of graphitic electrode.

FIRST-PRINCIPLE CALCULATION OF STRUCTURAL AND ELECTRONIC PROPERTIES OF ZINC-BLENDE ByAlxGa1-x-yN MATCHED TO AlN SUBSTRATE

2012 ◽  
Vol 26 (24) ◽  
pp. 1250159 ◽  
Author(s):  
LAKHDAR DJOUDI ◽  
ABDELHADI LACHEBI ◽  
BOUALEM MERABET ◽  
HAMZA ABID
Keyword(s):  
Electronic Properties ◽  
Density Functional ◽  
Strong Dependence ◽  
Theoretical Data ◽  
Lattice Parameter ◽  
Full Potential ◽  
Generalized Gradient ◽  
First Principle Calculation ◽  
Zinc Blende ◽  
Structural And Electronic Properties

The full-potential linearized augmented plane wave method (FP-LAPW) within density functional theory, using the generalized gradient approximation, is used to study the structural and electronic properties of zinc-blende B y Al x Ga 1-x-y N quaternary alloys that match the lattice of an AlN substrate. The range of compositions, for which the lattice of the alloy matches AlN , is determined. Our calculated band structure, density of states, electron density and lattice parameter for B y Al x Ga 1-x-y N allow to accurately evaluate the profound effect that the incorporation of small amounts of Boron have on structural and electronic properties of Al x Ga 1-x N alloys. A comparison of the ground state properties with the available experimental and theoretical data is made for the compounds related to B y Al x Ga 1-x-y N and of the Al x Ga 1-x N alloys. The results show a strong dependence of the band gap (as well as the lattice parameter) on the Boron content, which might make B y Al x Ga 1-x-y N materials promising and useful for optoelectronic applications.

scholarly journals Lattice disorder effect on magnetic ordering of iron arsenides

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Athena S. Sefat ◽  
Xiaoping P. Wang ◽  
Yaohua Liu ◽  
Qiang Zou ◽  
Mimgming Fu ◽  
...  
Keyword(s):  
Magnetic Coupling ◽  
Magnetic Ordering ◽  
Structural Features ◽  
Lattice Parameter ◽  
Chemical Compositions ◽  
Lattice Disorder ◽  
Local Lattice ◽  
Higher Temperature ◽  
Disordered Crystal ◽  
Planar Strain

AbstractThis study investigates magnetic ordering temperature in nano- and mesoscale structural features in an iron arsenide. Although magnetic ground states in quantum materials can be theoretically predicted from known crystal structures and chemical compositions, the ordering temperature is harder to pinpoint due to potential local lattice variations that calculations may not account for. In this work we find surprisingly that a locally disordered material can exhibit a significantly larger Néel temperature (TN) than an ordered material of precisely the same chemical stoichiometry. Here, a EuFe2As2 crystal, which is a ‘122’ parent of iron arsenide superconductors, is found through synthesis to have ordering below TN = 195 K (for the locally disordered crystal) or TN = 175 K (for the ordered crystal). In the higher TN crystals, there are shorter planar Fe-Fe bonds [2.7692(2) Å vs. 2.7745(3) Å], a randomized in-plane defect structure, and diffuse scattering along the [00 L] crystallographic direction that manifests as a rather broad specific heat peak. For the lower TN crystals, the a-lattice parameter is larger and the in-plane microscopic structure shows defect ordering along the antiphase boundaries, giving a larger TN and a higher superconducting temperature (Tc) upon the application of pressure. First-principles calculations find a strong interaction between c-axis strain and interlayer magnetic coupling, but little impact of planar strain on the magnetic order. Neutron single-crystal diffraction shows that the low-temperature magnetic phase transition due to localized Eu moments is not lattice or disorder sensitive, unlike the higher-temperature Fe sublattice ordering. This study demonstrates a higher magnetic ordering point arising from local disorder in 122.

Effect of TiO2 crystal form on the denitration performance of Ce–W–Ti catalyst

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Xue Bian ◽  
Yuntao Yu ◽  
Nana Hao ◽  
Wenyuan Wu
Keyword(s):  
Titanium Dioxide ◽  
Mixed Crystal ◽  
Surface Acidity ◽  
High Surface ◽  
Crystal Form ◽  
Large Specific Surface Area ◽  
Metatitanic Acid ◽  
Pure Phase ◽  
Crystal Phases ◽  
Better Than

Abstract Titanium dioxide supports, which were prepared by roasting metatitanic acid under different conditions, were used to prepare a series of Ce–W–Ti catalysts. The structure and denitration properties of the catalyst were studied. The results showed that TiO2 had different crystal types (mixed crystal phases with different proportions of anatase and rutile) under different roasting conditions, and the denitration efficiency of mixed crystal was better than that of pure phase TiO2. Ce–W/200 °C-1 hTiO2 catalyst exhibited a prominent NO conversion rate, and it can reach higher than 90% at a temperature range from 250 to 500°C. The large specific surface area, low content of rutile TiO2 in the support, high content of chemical adsorbed oxygen and high surface acidity were favorable to denitration performance of Ce–W–Ti catalyst.

Cluster, Surface and Bulk Properties of ZnCd Binary Alloys: Molecular-Dynamics Simulations

2005 ◽  
Vol 502 ◽  
pp. 51-56 ◽  
Author(s):  
Sakir Erkoc
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Density Functional ◽  
Structural Features ◽  
Bulk Materials ◽  
Bulk Properties ◽  
Atom Clusters ◽  
Dynamics Simulations ◽  
Mixed Clusters ◽  
Stable Structures

The structural and electronic properties of isolated neutral ZnmCdn clusters for m+n £ 3 have been investigated by performing density functional theory calculations at B3LYP level. The optimum geometries, vibrational frequencies, electronic structures, and the possible dissosiation channels of the clusters considered have been obtained. An empirical many-body potential energy function (PEF), which comprices two- and three-body atomic interactions, has been developed to investigate the structural features and energetics of ZnmCdn (m+n=3,4) microclusters. The most stable structures were found to be triangular for the three-atom clusters and tetrahedral for the four-atom clusters. On the other hand, the structural features and energetics of Znn-mCdm (n=7,8) microclusters, and Zn50, Cd50, Zn25Cd25, Zn12Cd38, and Zn38Cd12 nanoparticles have been investigated by performing molecular-dynamics computer simulations using the developed PEF. The most stable structures were found to be compact and three-dimensional for all elemental and mixed clusters. An interesting structural feature of the mixed clusters is that Zn and Cd atoms do not mix in mixed clusters, they come together almost without mixing. Surface and bulk properties of Zn, Cd, and ZnCd systems have been investigated too by performing molecular-dynamics simulations using the developed PEF. Surface reconstruction and multilayer relaxation on clean surfaces, adatom on surface, substitutional atom on surface and bulk materials, and vacancy on surface and bulk materials have been studied extensively.

Iron Chelation by thiocytosine: Investigating electronic and structural features for describing tautomerism and metal chelation processes

2021 ◽  
pp. 1-8
Author(s):  
Azadeh Jafari Rad ◽  
Maryam Abbasi ◽  
Bahareh Zohrevand
Keyword(s):  
Density Functional Theory ◽  
Dft Calculations ◽  
Molecular Orbital ◽  
Density Functional ◽  
Biological Systems ◽  
Iron Chelation ◽  
Structural Features ◽  
Metal Chelation ◽  
Functional Theory

This work was performed regarding the importance of iron (Fe) chelation for biological systems. This goal was investigated by assistance of a model of thiocytosine (TC) for participating in Fe-chelation processes. First, formations of tautomeric conformations were investigated to explore existence of possible structures of TC. Next, Fe-chelation processes were examined for all four obtained tautomers of TC. The results indicated that thiol tautomers could be seen at higher stability than thio tautomers, in which one of such thiol tautomers yielded the strongest Fe-chelation process to build FeTC3 model. As a consequence, parallel to the results of original TC tautomers, Fe-chelated models were found to be achievable for meaningful chelation processes or sensing the existence of Fe in media. Examining molecular orbital features could help for sensing purposes. The results of this work were obtained by performing density functional theory (DFT) calculations proposing TC compounds suitable for Fe-chelation purposes.

Engineering Modified Mesoporous Silica Catalysts through Porosity and Surface Acidity Control for Selective Production of DME

2021 ◽  
Vol 894 ◽  
pp. 45-49
Author(s):  
Rosanna Viscardi ◽  
Vincenzo Barbarossa ◽  
Raimondo Maggi ◽  
Francesco Pancrazzi
Keyword(s):  
Mesoporous Silica ◽  
Dimethyl Ether ◽  
Sulfonic Acid ◽  
Pore Diameter ◽  
Solid Acid ◽  
Surface Acidity ◽  
High Surface ◽  
High Surface Area ◽  
Bifunctional Catalysts ◽  
Scanning Electronic Microscopy

DME has been received the attention as a renewable energy due to its thermal efficiencies equivalent to diesel fuel, lower NOx emission, near-zero smoke and non-toxic. DME can be obtained by methanol dehydration over solid acid catalysts or directly from syngas over bifunctional catalysts. The catalytic dehydration of methanol to DME has been widely studied in the literature over pure or modified γ -aluminas (γ-Al2O3) and zeolites. Mesoporous silica has obtained much consideration due to its well-defined structural order, high surface area, and tunable pore diameter. In this work, sulfonic acid and aluminium modified mesoporous silica were synthesized and tested as catalysts for production of dimethyl ether from methanol. The modified silicas were studied utilizing XRD, N2 physisorption, pyridine adsorption, and scanning electronic microscopy. The effects of reaction temperature and water deactivation on the methanol selectivity and conversion to dimethyl ether were investigated. Sulfonic acid modified mesoporous silica showed higher selectivity and stability of DME than that of aluminosilicate. The grafting of mesoporous silica with sulfonic groups displayed much more enhanced hydrothermal stability than Al-MCM-41 and γ-Al2O3.

Physical properties of chalcopyrite-type Cu1−xAgxGaTe2 by first-principles study

2016 ◽  
Vol 30 (30) ◽  
pp. 1650373 ◽  
Author(s):  
Li Xue ◽  
Yi-Ming Ren ◽  
Zheng-Long Hu
Keyword(s):  
Thermal Conductivity ◽  
Elastic Constants ◽  
Density Functional ◽  
Lattice Thermal Conductivity ◽  
Lattice Parameter ◽  
Functional Theory ◽  
Lattice Volume ◽  
Te Material ◽  
Ag Substitution ◽  
Good Agreement

[Formula: see text] is a promising thermoelectric (TE) material for high temperature TE applications. This work systematically investigated the structural, elastic and thermodynamic properties of [Formula: see text] ([Formula: see text] = 0, 0.25, 0.5, 0.75 and 1) by density functional theory. The calculated lattice volume is expanded with the increase of Ag content, but this expansion is anisotropic. The lattice parameter along [Formula: see text]-axis is linear expansion, and along [Formula: see text]-axis is parabolic expansion, which is in good agreement with available experimental data. The phase stability of [Formula: see text] alloy is studied by analyzing the formation energy, cohesive energy and elastic constants. Shear modulus, Young’s modulus, sound velocities, Debye temperature and the minimum thermal conductivity are obtained from the calculated elastic constants. The results show that Ag substitution could reduce the lattice thermal conductivity, which is helpful for improving the TE properties of [Formula: see text].

scholarly journals Ab initio calculations of structural, elastic, electronic and thermodynamic properties of the cerium filled skutterudite CeRu4P12 under the effect of pressure

2015 ◽  
Vol 33 (4) ◽  
pp. 699-708 ◽  
Author(s):  
Mokhtar Berrahal ◽  
Mohammed Ameri ◽  
Y. Al-Douri ◽  
U. Hashim ◽  
Dinesh Varshney ◽  
...  
Keyword(s):  
Thermodynamic Properties ◽  
Bulk Modulus ◽  
Density Functional ◽  
Debye Model ◽  
Lattice Parameter ◽  
Full Potential ◽  
Generalized Gradient ◽  
Filled Skutterudite ◽  
Effect Of Pressure ◽  
Lmto Method

AbstractThe paper presents an investigation on crystalline, elastic and electronic structure in addition to the thermodynamic properties for a CeRu4P12 filled skutterudite device by using the full-potential linear muffin-tin orbital (FP-LMTO) method within the generalized gradient approximations (GGA) in the frame of density functional theory (DFT). For this purpose, the structural properties, such as the equilibrium lattice parameter, bulk modulus and pressure derivatives of the bulk modulus, were computed. By using the total energy variation as a function of strain we have determined the independent elastic constants and their pressure dependence. Additionally, the effect of pressure P and temperature T on the lattice parameters, bulk modulus, thermal expansion coefficient, Debye temperature and the heat capacity for CeRu4P12 compound were investigated taking into consideration the quasi-harmonic Debye model.

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