Experimental Lattice Parameters Research Articles

Structural and Thermodynamic Properties of TiC x N y O z Solid Solution: Experimental Study and First-Principles Approaches

A series of TiC x N y O z solid solutions were synthesized via solid-state reaction and XRD patterns exhibited a single phase of FCC structure over the whole concentration range. The structural and thermodynamic properties of TiC x N y O z solid solutions were studied using experimental method and first-principles calculations. The difference between the calculated and experimental lattice parameters could be attributed to the vacancies segregated in TiO part. The fitting formulae for lattice parameters and mixing enthalpies were firstly given for TiC x N y O z solid solution over the whole concentration range. The obtained thermodynamic data for TiC x N y O z solid solution properly explained the reaction sequence of the carbothermal reduction of TiO2, providing theoretical foundation for TiC x N y O z solid solution as a kind of prospective material for consuming anode utilized in USTB titanium electrolysis process.

Choice of hybrid functional and basis set optimization to calculate the structural, electronic, mechanical, and vibrational properties of BaSnO3

This work aimed to study the influence of seven hybrid functionals (B3LYP, B1WC, B3PW, PBE0, PBESOL0, SOGGAXC, and WC1LYP) and selected basis sets in the CRYSTAL software library on the calculated structural, electronic, mechanical, and vibrational properties of BaSnO3 under the framework of periodic density functional theory. Based on the results showing the best approximation of the experimental band gap energy and lattice parameter, the PBE0 functional and the Baranek basis set were used to optimize the outer valence shell functions, αsp and αd, in order to improve the quality of calculated properties. An analysis was done to determine the density of states, band structure, elastic constants, and infrared (IR) active modes. The results were compared with other reported quantum mechanical calculations and available experimental data.

Ab initiophonon dispersion in crystalline naphthalene using van der Waals density functionals

Acene molecular crystals are of current interest in organic optoelectronics, both as active materials and for exploring and understanding new phenomena. Phonon scattering can be an important facilitator and dissipation mechanism in charge separation and carrier transport processes. Here, we carry out density functional theory (DFT) calculations of the structure and the full phonon dispersion of crystalline naphthalene, a well-characterized acene crystal for which detailed neutron-diffraction measurements, as well as infrared and Raman spectroscopy, are available. We evaluate the performance, relative to experiments, of DFT within the local density approximation (LDA); the generalized gradient approximation of Perdew, Burke, and Ernzerhof (PBE); and a recent van der Waals--corrected nonlocal correlation (vdW-DF-cx) functional. We find that the vdW-DF-cx functional accurately predicts lattice parameters of naphthalene within 1%. Intermolecular and intramolecular phonon frequencies across the Brillouin zone are reproduced within 7.8% and 1%, respectively. As expected, LDA (PBE) underestimates (overestimates) the lattice parameters and overestimates (underestimates) phonon frequencies, demonstrating their shortcomings for predictive calculations of weakly bound materials. If the unit cell is fixed to the experimental lattice parameters, PBE is shown to lead to improved phonon frequencies. Our study provides a detailed understanding of the phonon spectrum of naphthalene, and highlights the importance of including van der Waals dispersion interactions in predictive calculations of lattice parameters and phonon frequencies of molecular crystals and related organic materials.

Hydrogenation induced structure and property changes in GdGa

Hydrides GdGaHx were obtained by exposing the Zintl phase GdGa with the CrB structure to a hydrogen atmosphere at pressures from 1.5 to 50bar and temperatures from 50 to 500°C. Structural analysis by powder X-ray diffraction suggests that conditions with hydrogen pressures in a range between 15 and 50bar and temperatures below 500°C afford a uniform hydride phase with the NdGaH1.66 structure (Cmcm, a=3.9867(7) Å, b=12.024(2) Å, c=4.1009(6) Å) which hosts H in two distinct positions, H1 and H2. H1 is coordinated in a tetrahedral fashion by Gd atoms, whereas H2 atoms are inserted between Ga atoms. The assignment of the NdGaH1.66 structure is corroborated by first principles DFT calculations. Modeling of phase and structure stability as a function of composition resulted in excellent agreement with experimental lattice parameters when x=1.66 and revealed the presence of five-atom moieties Ga-H2-Ga-H2-Ga in GdGaH1.66. From in situ powder X-ray diffraction using synchrotron radiation it was established that hydrogenation at temperatures above 200°C affords a hydride with x≈1.3, which is stable up to 500°C, and that additional H absorption, yielding GdGaH1.66, takes place at lower temperatures. Consequently, GdGaH1.66 desorbs H above T=200°C. Without the presence of hydrogen, hydrides GdGaHx decompose at temperatures above 300°C into GdH2 and an unidentified Gd-Ga intermetallics. Thus the hydrogenation of GdGa is not reversible. From magnetic measurements the Curie-Weiss constant and effective magnetic moment of GdGaH1.66 were obtained. The former indicates antiferromagnetic interactions, the latter attains a value of ~8 μB which is typical for compounds containing Gd3+ions.

Stability of the different AlOOH phases under pressure

The pressure effects on three different AlOOH structures (α, γ, and δ phases) are systematically analyzed by density functional theory with different exchange and correlation energy functional approximations, namely two local, two generalized-gradient approximation (GGA), and two GGA for solids (GGAsol). Phase stability, compressibility and hydrogen bond evolution are studied in a range of pressures from 0 to 30 GPa. In general, the use of GGAsol functionals is mandatory in order to have the correct phase stability order, a good description of the hydrogen bonds, and a close agreement with the experimental lattice parameters at the various pressures. Pressure-induced hydrogen-bond symmetrization is found in γ and δ phases at high compression, while the hydrogen bonds in the α phase remain asymmetric. A detailed analysis of the uncertainties on the values of the bulk moduli and their pressure derivative at zero pressure deduced by fitting calculated or experimental (P,V) data is also presented.

Swift heavy ion irradiated spinel ferrite: A cheap radiation resistant material

Effect of (80MeV) 16O 6+ ion irradiation on the structural properties and cation distribution of the as-burnt samples (i.e. the samples are without any thermal/sintering treatment) with the following compositions: MnFe2O4, Mn0.5Zn0.5Fe2O4 and ZnFe2O4 prepared by sol–gel auto-combustion technique have been studied through in-situ and ex-situ X-ray diffraction (XRD) technique. Well characterized single phase MnFe2O4 and Mn0.5Zn0.5Fe2O4 samples were irradiated at fluence 1×1011, 1×1012, 1×1013 and 1×1014ions/cm2 to see the effect of the electronic energy loss induced changes in the structural properties and in cation distribution monitored through ex-situ XRD. ZnFe2O4 samples were irradiated with ion fluence values ranging between 1×1011−2×1014ions/cm2 to observe the effect of in-situ XRD on structural properties and cation distribution. Results very clearly depict the redistribution of cations in the samples, which show noticeable changes in: ionic radii of A-site (rA) and B-site (rB), experimental and theoretical lattice parameter (aexp.,ath.), unit cell volume (V), Scherrer’s Grain diameter (D), oxygen positional parameter (u), tetrahedral and octahedral bond length (RA, RB), shared tetrahedral and octahedral edge (dAE,dBE) and bond angles (θ1, θ2, θ3, θ4, θ5). Results are interpreted in terms of irradiation induced changes in the above mentioned parameters.

Structural, electrical and microwave properties of (Sr0.6Ca0.4) (CoyMn1−y) O3 (0.2 ≤ y ≤ 1.0) thick film ceramics

Purpose – This paper aims to study the structural, electrical and microwave properties of (Sr0.6Ca0.4) (CoyMn1−y) O3 (0.2 ≤ y ≤ 1.0) thick-film ceramics. Design/methodology/approach – The thick films of (Sr0.6Ca0.4) (CoyMn1−y) O3 (0.2 ≤ y ≤ 1.0) on the alumina substrate have been delineated using screen printing technique. The structural analysis was carried out using an X-ray diffraction method and scanning electron microscopy. The direct current (DC) electrical resistivity is measured using a two-probe method. Microwave absorption was studied in the 8-18 GHz frequency range by using the Waveguide Reflectometer Method. The permittivity and permeability in the 8-18 GHz frequency range were measured by using Voltage Standing Wave Ratio slotted section method. Findings – The thick films have orthorhombic perovskite structure with dominant (020) plane. By using first-principle calculation method, theoretical and experimental lattice parameter and cell volume of (Sr0.6Ca0.4) (CoyMn1−y) O3 are matched with each other. The cobalt content changes the morphology from plates to needles. The DC electrical resistivity increases with increase in Co content and decreases with increase in temperature. (Sr0.6Ca0.4) (CoyMn1−y) O3 thick film shows 75 per cent microwave absorption both in the X band and Ku band. The microwave permittivity and permeability decreases with increase in frequency and Co content. Originality/value – Structural, electrical and microwave properties of (Sr0.6Ca0.4) (CoyMn1−y) O3 (0.2 ≤ y ≤ 1.0). Thick film ceramics on alumina substrate is reported for the first time.

Effect of pressure on the valency of cerium in cerium monochalcogenides and cerium monopnictides

Application of pressure on a material changes its properties due to the modification of the electronic states of the constituent atoms. Various effects of pressure on the properties of solid material have been identified, and valency change of an element in a compound is one of the effects of pressure. This study was aimed at finding the valency change as a function of pressure of some compounds. The valency changes of cerium in cerium monochalcogenides CeX (X = O and S) and cerium monopnictides CeX (X = P and As) as functions of pressure have been calculated utilising the reported data. For calculating the valency change of Ce, the reported experimental pressure-volume relationships of CeO, CeS, CeP and CeAs have been reproduced using the Birch equation of state. The corresponding pressure-volume relationships of these compounds for stable trivalent cerium have also been calculated using the same Birch equation. The change in valency is calculated by a technique, which considers the difference between the calculated and experimental lattice parameters at each pressure value of the concerned compound. Clear effect of pressure on the cerium valency has been obtained for each compound from the present calculation. J.Natn.Sci.Foundation Sri Lanka 2015 43 (4): 313 - 317

Revealing the influence of the compression mechanism on the electronic structure and the related properties of CrF3

The influence of the compression mechanism on the unit cell of CrF3 is investigated by means of density functional theory. The experimental lattice parameters under different pressure values starting from the ambient pressure up to 9.12 GPa were optimized so as to relax the crystalline structures. To ascertain the effect of pressure on the structural properties, the electronic band structure, density of states, Fermi surface and chemical bonding were calculated. The electronic band structure explored the metallic nature of CrF3 and the density of states confirmed that. The density of states at Fermi level and the specific heat coefficient were obtained at different pressure values which show significant reduction occurs with increasing the pressure. It has been found that the pressure cause to push Cr-s/p orbitals to hybridize with F-s orbital at high energy region between 14.0 eV and 15.0 eV. Also it cause a small octahedral strain and reduce the bond lengths and angles in good agreement with the experimental values. Increasing the pressure leads to change the shape of Fermi surface. Further deep insight into the electronic structure can be obtained from the optical dielectric functions. The calculated optical properties confirmed that the pressure cause significant influence of the structure of CrF3.

Force field for realistic molecular dynamics simulations of ZrO2 growth

The paper primarily deals with the development of an interaction potential (force field) for a realistic description of atom-by-atom ZrO2 growth. Owing to the fact that for many metal oxides including ZrO2 only full-charge (Zr+4 and O−2) interaction potentials are available, special attention is paid to the effect of the Zr and O elemental charges. Parameters of the short-range part of the interaction potential leading to experimental lattice parameters and formation energies have been identified in a wide range of elemental charges. Molecular dynamics simulations of ZrO2 growth reveal that the structures grown using the presently available full-charge interaction potentials are in contradiction with an experiment (the atoms have too low coordination numbers). Simulations using a wide range of newly fitted full-charge and partial-charge interaction potentials reveal that the results depend (in addition to the fitting procedure) on the elemental charges. Correct partial charges and potential parameters leading to experimentally relevant structures (with correct coordination numbers) have been identified and used.

Electronic structure, optical dielectric constant and born effective charge of EuAlO3

EuAlO3 (EAO) is synthesized by the sol–gel process. The Rietveld refinement of the X-ray diffraction data shows that the material has orthorhombic structure with Pbnm space group. The density functional theory calculations are initiated with the experimental lattice parameters. The full potential linearized augmented plane wave method and projector augmented wave method are used to investigate the ground state properties of EAO. An indirect band gap of 1.8eV is observed with the valence band maximum at the Γ point and the conduction band minimum at the R point. The X-ray photoemission spectroscopy (XPS) spectra of EAO are obtained in the energy window of 0–1000eV. Using the electronic density of states, the valence band (VB) spectrum of EAO is generated and compared with the observed VB-XPS spectrum. The optical dielectric constant and the refractive index of the material are calculated for the photon energy radiation. The optical properties show a considerable anisotropy in the material. The Born effective charge of various elements and the dielectric tensor of EAO have been calculated.

Solution-combustion synthesized aluminium-doped spinel (LiAl x Mn2−x O4) as a high-performance lithium-ion battery cathode material

High-performing LiAl x Mn2−x O4 (x = 0, 0.125, 0.25, 0.375, and 0.5) spinel cathode materials for lithium-ion battery were developed using a solution combustion method. The as-synthesized cathode materials have spinel cubic structure of LiMn2O4 without any impurity peak and accompanied with peak shift as doping with aluminium. LiAl0.375Mn1.625O4 (first cycle capacity = 113.1 mAh g−1) retains 85 % (96.2 mAh g−1), while pristine LiMn2O4 electrode (first cycle capacity = 135.8 mAh g−1) fades quickly and retains only 54 % (73.9 mAh g−1) after 50 cycles. The electrochemical performance of all the cathode samples prepared using the SCM is comparable to those reported for Al-doped LiMn2O4 spinel cathode materials. The experimental lattice parameter of LiAl x Mn2−x O4 was validated by ab initio calculations and correlated with the first cycle capacity of materials. The variation in lattice parameter as a result of Al doping greatly enhanced the cyclability of discharge capacity of the LiMn2O4 spinel.

Theoretical investigation of new Heusler alloys Ru2VGa1−xAlx

Results of first-principles full-potential linearized augmented plane wave calculations of elastic and related electronic and thermodynamic properties of the quaternary Heusler alloys Ru2VAlxGa1−x (x=0, 0.25, 0.5, 0.75, 1) are presented. These materials were found to have the L21 structure for all concentrations. The agreement between the theoretical and experimental lattice parameters for both Ru2VAl and Ru2VGa at various temperatures was found to be satisfactory. Our results provide predictions for the remaining mixed more» Heusler alloys Ru2VAlxGa1−x (0<x<1) for which no direct experimental or theoretical data are presently available. In their equilibrium L21 structure, all concentrations are non-magnetic metals. A linear variation of the lattice parameter, bulk modulus, elastic constants and Debye temperature has been observed with x.

Stability and magnetic properties of cobalt nitrides

Magnetic cobalt nitrides were synthesized via nitriding of cobalt particles under NH3 flux by a multi-step process that includes annealing at two temperatures: 823K and 623K. The phases Co4+xN and Co3N1+y were produced and their structure and magnetic properties were studied. Both phases are found to be ferromagnetic with saturation magnetization of 143Am2kg−1 and 33Am2kg−1 respectively and decompose above 650K, before attaining the Curie temperature. Self-consistent Density Functional Theory (DFT) calculations were performed to understand the nitrides structure and magnetic behavior dependence on stoichiometry. The results indicate that the magnetic behavior of the hexagonal nitride is strongly dependent on the nitrogen content. The comparison of the experimental lattice parameters and magnetization values with the DFT calculations allows to determine the stoichiometry of the prepared compounds.

Improved Calculation of the Electronic and Optical Properties of Tetragonal Barium Titanate

The electronic and optical properties of tetragonal barium titanate (BaTiO3) have been investigated by use of first-principles density functional theory on a plane wave basis, by use of norm-conserving pseudopotentials in the localized density approximation. For accuracy, experimental lattice parameters reported in the literature were used. The band structure, total and partial density of states (DOS), and Born effective charges of tetragonal BaTiO3 were obtained from first-principles calculations. The partial DOS and Born effective charges indicate that the Ti–O bonds are partially covalent and the Ba–O bonds are partially ionic. The complex dielectric functions for ordinary and extraordinary optical polarization were calculated, and were in reasonable agreement with those from previous first-principles calculations. The refractive index, extinction coefficient, reflectivity, and energy-loss spectrum for both types pf polarization were calculated from the complex dielectric function; the results obtained were an improvement on other published results.

Synthesis and soft magnetic properties of Zn0.8−xNixMg0.1Cu0.1Fe2O4 (x = 0.0−0.8) ferrites prepared by sol–gel auto-combustion method

Single phase nanocrystalline Zn0.8−xNixMg0.1Cu0.1Fe2O4 (x=0.0−0.8), were synthesized by sol–gel auto-combustion method without post-preparation treatment and, effect of Ni content on structural and magnetic properties is studied by X-ray diffraction (XRD), magnetic measurements and cation distribution. Scherrer’s grain diameter range between 23.5 and 35.1nm. Experimental and theoretical lattice parameter values suggest that the estimated cation distribution is close to the real distribution. Change in Ni-content leads to variation in cation distribution at site A and B. Ni2+ ions occupy both A and B site, but when Zn2+ is fully replaced by Ni2+, it totally goes to A site. Both coercivity measured at 50Hz and quasi static coercivity value is found to increase with nickel content. Same trend is observed for anisotropy constant values. Best magnetization value of 25.04emu/g was obtained for the specimen with x=0.60. Variation of magnetic properties and other parameters (obtained via cation distribution) can be understood in terms of observed changes in distribution of cation(s) on A and B site.

Magnetic Ground State and Electronic Structure Calculations of PbMnO&lt;sub&gt;3&lt;/sub&gt; Using DFT

Structural optimization, magnetic ground state and electronic structure calculations of tetragonal PbMnO3have been carried out using local density approximation (LDA) implementations of density functional theory (DFT). Structural optimizations were done on tetragonal P4mm (non-centrosymmetric) and P4/mmm (centrosymmetric) structures using experimental lattice parameters and our results indicate that P4mm is more stable than P4/mmm. In order to determine the stable magnetic ground state of PbMnO3, total energies for different magnetic configurations such as nonmagnetic (NM), ferromagnetic (FM) and antiferromagnetic (AFM) were computed for both P4mm and P4/mmm structures. The total energy results reveal that the FM non-centrosymmetric structure is found to be the most stable magnetic ground state. The electronic band structure, density of states (DOS) and the electron localization function (ELF) were calculated for the stable FM structure. ELF revealed the distorted non-centrosymmetric structure. The band structure and DOS for the majority spins of FM PbMnO3showed no band gap at the Fermi level. However, a gap opens up at the Fermi level in minority spin channel suggesting that it could be a half-metal and a potential spintronic candidate.

The Influence of Zn&amp;lt;sup&amp;gt;2+&amp;lt;/sup&amp;gt; Ions Substitution on the Microstructure and Transport Properties of Mn-Zn Nanoferrites

The effect of Zn2+ ions on the microstructure and electrical properties of Mn1-xZnxFe2O4 (0.0 ≤ x ≤ 0.5 in steps of 0.1) through a solid state reaction has been investigated. The structural properties have been investigated using X-ray diffraction (XRD) technique. The XRD analysis confirms that all samples are in a single-phase cubic spinel structure. The experimental lattice parameter (aexp) was decreased with increasing Zn2+ ions substitution due to the smaller ionic radius of zinc content. The crystallite size (t) of samples was estimated by Scherrer’s formula and found in the range (90 - 115 nm). Dc electrical resistivity and Seebeck voltage coefficients were measured as a function of temperature using the two probe methods. The temperature variation of resistivity exhibits two breaks, each break referring to a change in the activation energy. The Curie temperature estimated from dc resistivity measurement decreases with increasing Zn2+ ions. Seebeck voltage coefficient measurements reveal n-type conduction for all samples.

Effect of doping on the structural parameters of pure and doped barium titanate nano powders synthesised by sol-gel emulsion technique

Ba1-xDxTiO3, ceramic powders was synthesised using sol-gel-emulsion technique. Structure of the synthesised powders was analysed using X-ray diffractometer from which the lattice parameters were deduced. Effect of doping as a function of atomic radii and the concentration of dopant (D) was studied on these parameters. XRD analysis showed the synthesised material to possess pseudocubic symmetry. Crystallite size of these powders varied between 15.98–40.72 nm. Cell volume shrinkage observed on doping pure BaTiO3 was noted to be between 0.02–2.27%. Change in % tetragonality for the synthesised powders was 16.62–21.57. The experimental lattice parameter values matched more closely when calculated using the empirical formula devised by Jiang et al. than that using Rick Ubic. The |%error| assuming six-fold coordination for the doped BaTiO3 powders was between 0.0168% to 0.9314% using the empirical formula devised by Jiang et al. and 0.0296% to 1.0852% using the formula given by Rick Ubic.

Nonmetal sublattice population induced defect structure in transition metal aluminum oxynitrides

The influence of oxygen concentration on the structure and mechanical properties of V0.5Al0.5OxN1−x thin films (0 ≤ x ≤ 0.8) was investigated. The unexpected experimental lattice parameter decrease with increasing oxygen concentration can be understood based on ab initio data: the oxygen incorporation induced formation of metal vacancies reduces the equilibrium volume and stabilizes the metastable solid solutions. Charge balancing is identified as the underlying physical mechanism by Bader decomposition analysis. Hence, property predictions for these oxynitrides are only meaningful if the defect structure is described.