Properties Of Alkaline Earth Oxides Research Articles

New Formulation of Equation of State and Study of Elastic Properties of Alkaline Earth Oxides under High Pressure

New Formulation of Equation of State and Study of Elastic Properties of Alkaline Earth Oxides under High Pressure

DFT calculations of the local structures and the EPR parameters for Rh2+ doped AO (A = Mg, Ca) crystals

The local structures for Rh2+ centers in AO (A = Mg and Ca) are theoretically studied using density functional theory (DFT) with periodic CP2K program. Through geometry optimization, the ground state structures and the electronic properties with the minimal energies are obtained for both systems. Rh2+ is found to occupy the host A in AO, associated with the uniform expansion of 3.61% and shrinkage of 2.18% and the additional relative elongations of 1.97% and 3.52% for Mg and Ca, respectively, along the [0 0 1] (C4) axis due to the Jahn-Teller effect. The corresponding electron paramagnetic resonance (EPR) parameters, g and hyperfine coupling tensors, are calculated in ORCA level. The present results are discussed and compared with those of the previous calculations based on the perturbation formulas of the EPR parameters. Present study would be helpful to the systematic understanding of the local structural and electronic properties of alkaline earth oxides with Rh2+ dopants.

First-principles calculations of the electronic, magnetic and optical properties of rhenium-doped alkaline earth oxides

The electronic, magnetic and optical properties of alkaline earth oxides XO (X = Ca, Sr, Ba) doped with 5d transition metal rhenium (Re) were investigated by applying first-principles calculations within the treatment of density functional theory based on a full potential linearised augmented plane wave method. 5d transition metal atom Re was doped to replace Ca/Sr/Ba atoms with 12.5% concentration to form the supercells. Density of states and band structures predict half-metallic characteristics of the supercells X0.875ORe0.125 (X = Ca, Sr, Ba). Half-metallic band gaps were observed clearly in the spin up majority channel around the Fermi level (EF). Dopant 5d transition metal atom Re creates a spin magnetic moment (μB) in the supercells X0.875ORe0.125 (X = Ca, Sr, Ba). Optical parameters (dielectric function ε(ω), absorption coefficient and reflectivity) were discussed. Materials exhibiting properties like absorption, reflectivity and half-metallic can be applicable for optoelectronics and spintronics devices.

Structural elastic and thermal properties of SrxCd1−x O mixed compounds — a theoretical approach

Abstract In the present paper, the structural and mechanical properties of alkaline earth oxides mixed compound SrxCd1−x O (0 ≤ x ≤ 1) under high pressure have been reported. An extended interaction potential (EIP) model, including the zero point vibrational energy effect, has been developed for this study. Phase transition pressures are associated with a sudden collapse in volume. Phase transition pressure and associated volume collapses [ΔV (Pt)/V(0)] calculated from this approach are in good agreement with the experimental values for the parent compounds (x = 0 and x = 1). The results for the mixed crystal counterparts are also in fair agreement with experimental data generated from the application of Vegard’s law to the data for the parent compounds.

Isobaric Study of the Elastic Properties for Alkaline Earth Oxides under High Temperature

A simple and straightforward theoretical model is developed to investigate the elastic properties of alkaline earth oxides under the effect of temperature as well as pressure. The calculation is performed with the help of high pressure-high temperature equation of state based on thermodynamic analysis. The anharmonic term arising due to thermal expansion has been taken into account in the expansion of logarithmic series of the thermodynamic data. The results obtained for alkaline earth oxides are discussed and compared with experimental data under the combined effect of high temperature and high pressure. The results are found to be in good agreement with available experimental results.

Effect of temperature on elastic properties of alkaline earth oxides (AEO)

A simple and straightforward theoretical model is developed to investigate the elastic properties of alkaline earth oxides under the effect of temperature as well as pressure. The calculation are performed with the help of high pressure-high temperature equation of state (EOS) based on thermodynamic analysis. The anharmonic term arising due to thermal expansion, has been taken into account in the expansion of logarithmic series of the thermodynamic data. The results obtained for alkaline earth oxides are discussed and compared with experimental data under the effect of high temperature at zero pressure. The results are found to be in good agreement with available experimental results and thus may be helpful in analyzing the other's experimental results.

Elastic properties of alkaline earth oxides under high pressure

In this article, we have investigated the high-pressure structural phase transition of alkaline earth oxides using the three-body potential (TBP) model. Phase transition pressures are associated with elastic constants. An effective inter-ionic interaction potential (TBP) with long-range Coulomb interactions and the Hafemeister–Flygare type short-range overlap repulsion and the vdWl interaction is developed. The present calculations have revealed reasonably good agreement with the available experimental data on structural transition (B1–B2 structure). The phase transition pressures Pt of MgO, CaO, SrO, and BaO occur at 220, 45, 40, and 100 GPa, respectively. Further, the variations of the second-order elastic constants with pressure have followed a systematic trend, which are almost identical to those exhibited by the observed data measured for other semiconducting compounds with rocksalt (B1)-type crystal structure. It is found that TBP promises that we would be able to predict phase transition pressure and elastic constants for other chalcogenides as well. The results may be useful for geophysical study.

Temperature Dependence of Elastic Constants of Alkaline Earth Oxides

The elastic properties of alkaline earth oxides (AEOs) under high temperature are discussed within the framework of many body Lundqvist potential incorporating the contribution of thermal phonon pressure. The short-range repulsive interaction is taken up to the second nearest neighbors. The derived expressions are used to compute the values of second-order elastic constants (SOECs) and bulk modulus of alkaline earth oxides at different temperatures (300<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mmultiscripts><mml:mtext>K</mml:mtext><mml:mprescripts /><mml:none /><mml:mn>&#x00b0;</mml:mn></mml:mmultiscripts></mml:mrow></mml:math>&#8211;2000<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mmultiscripts><mml:mtext>K</mml:mtext><mml:mprescripts /><mml:none /><mml:mn>&#x00b0;</mml:mn></mml:mmultiscripts></mml:mrow></mml:math>). The results are found to be satisfactory and are in agreement with available experimental and the theoretical results.

Elastic properties of alkaline earth oxides under high pressure

A phenomenological theory has been developed to describe the elastic behavior of alkaline earth oxide solids under high pressure. The values of second order elastic constants, Cauchy's deviation and Zener anisotropy ratio at different pressures have been computed for MgO, CaO, SrO, and BaO. The results were found to be satisfactory and in agreement with available experimental and other theoretical results.

Structure, Texture, and Acid‐Base Properties of Alkaline Earth Oxides, Rare Earth Oxides, and Binary Oxide Systems

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Structure, Texture, and Acid-Base Properties of Alkaline Earth Oxides, Rare Earth Oxides, and Binary Oxide Systems

The effect of synthesis conditions on the formation of the phase composition, dispersity, pore structure, and acid-base properties of alkaline earth oxides, rare earth oxides, and the Mg-M-O (M = Y, La, or Ce) and Y(La)-M-O (M = Ca, Sr, or Ba) binary systems was studied. It was found that the nature of the system was responsible for the character of phase transformations: the Mg-M-O samples were a mixture of either MgO with Y2O3 or MgO with a solid solution based on rare earth oxides (LaMg)2O3 or (CeMg)O2); the Y(La)-M-O samples (M = Ca, Sr, or Ba) contained the M2Y2O5, MY2O4, and MLa2O4 compounds, which differ in chemical stability, in addition to La2O3 and Y2O3 phases. According to XPS data, the M/Mg atomic ratios were much higher than the bulk values; this is indicative of an enrichment of the surface of samples in the second component. An increase in the concentration of M2O3 from 5 to 25 mol % resulted in a decrease in the S sp of the Mg-M-O samples from 220 ± 10 to 110 ± 10 m2/g; the S sp of samples calcined at 750°C was lower by a factor of ∼1.5–2. The S sp of the Y(La)-M-O samples was higher than the S sp of individual La2O3 and Y2O3. The samples were characterized by a biporous texture. The concentrations and strength distributions of surface OH groups, Lewis acid sites, and Lewis base sites depend on the nature and concentration of rare earth elements in the binary samples. The activity of the Mg-M-O samples in the oxidative dehydrogenation reaction of propionitrile correlated with the acid-base surface sites. Among the Ru/Y(La)-M-O catalysts for ammonia synthesis, Ru/Y-Ba-O was the most active; this catalyst provided a higher yield of NH3 at 250–300°C, as compared with catalysts prepared with the use of other supports (Sibunit, KVU-1, and C/MgO).

Hexane—carbon dioxide reaction catalyzed by alkaline earth oxides: I. Catalytic Behaviour and Intermediate

The hexane—carbon dioxide reaction was carried out at 1173 K in order to study the catalytic properties of alkaline earth oxides and the reaction intermediate for the gasification. The catalytic activities of these oxides depended upon both the nature of the alkaline earth and the starting material. Magnesium oxide, prepared from the basic carbonate or calcium oxide, showed high catalytic activity, whereas strontium and barium oxides were inactive due to an inability to form the carbonaceous intermediate. Hexane was thermally decomposed in the gas phase to give C 1 C 3 hydrocarbons, hydrogen and a carbon precursor. C 1 C 3 hydrocarbons scarcely interacted with the catalyst. The carbon precursor was captured by the active catalyst to give carbon which was the intermediate for catalytic gasification.

Surface properties of alkaline earth oxides as studied by UV-visible diffuse reflectance spectroscopy

The merits of UV-visible diffuse reflectance spectroscopy for the study of surface phenomena on microcrystalline MgO, CaO and SrO are described and illustrated. It is shown that surface states ascribable to anions in 5-, 4- and 3-coordination can be observed and their respective interactions with adsorbed gases investigated. The behaviour of a series of XH molecules towards heterolytic dissociative chemisorption are reviewed, and shown to correlate with their acidities. With ammonia, where non-dissociative adsorption can accompany heterolytic chemisorption, the surface anions of the alkaline earth oxides exhibit strong UV charge-transfer absorption. Analogy is drawn with the behaviour of ammonia in developing charge-transfer-to-solvent spectra with anions in solution. Finally, the propensity of the alkaline earth oxides to produce anions from adsorbed molecules is treated further, and special reference is made to pyridine and to carbon monoxide, where UV-visible spectra show that adsorbed anions couple to give more complex resonance-stabilized structures.

Study of Anharmonic Properties of Alkaline Earth Oxides

AbstractThe third order elastic constants, pressure derivatives of second order elastic constants, Anderson‐Grüneisen parameters, and second Grüneisen constants are calculated for alkaline earth oxides with the help of a new interionic potential. The potential consists of Hafemeister and Zarht (HZ) type short‐range overlap repulsion, effective up to second neighbours, van der Waals (vDW), and three‐body interaction (TBI) effects. The vDWI coefficients are calculated from the Slater‐Kirkwood variational method. The results obtained are in good agreement with experimental data.

Investigation of mechanical properties of alkaline-earth oxides. I. Cohesive energy function

An analysis of several calculations of the physical properties of ionic crystals and of the experimental data on the elastic moduli of alkaline-earth oxides is used to propose a semiempirical cohesive energy function, which includes not only the pair interactions of ions described by the Born-Mayer potential, but also three-body interactions. The parameters of the cohesive energy function are determined for these crystals by fitting to the experimental values of the binding energies, lattice constants, and second-order elastic moduli.

Role of Three‐Body Interactions in Cohesive and Thermophysical Properties of Alkaline Earth Oxides

AbstractThe cohesive and thermophysical properties of alkaline earth oxides are thoroughly investigated by extending Hafemeister and Flygare (HP) and Hafemeister and Zarht (HZ) potentials to include the three‐body interaction effects. The extended HZ potential thus obtained is found to yield a better description of the above properties than those revealed by the extended HF potential presented and many other potentials used by earlier workers.

Properties of alkaline earth oxides in the crystalline state

Three different interaction potential functions suggested recently have been employed to calculate the cohesive energies, atomization energies, force constant, i.r. absorption frequency, and Debye temperature of the oxides of Be, Mg, Ca, Sr and Ba. The electron affinity of O 2− ion has been computed from these potentials by two different methods and the average value obtained is 728·7 kJ mole −1. The experimental values of the cohesive energies have been obtained by an indirect method for comparison. In all cases the theoretical values are in agreement with the available experimental values. This communication shows the validity of the new logarithmic interaction potential functions in the case of the alkaline earth oxides.

Thermal Properties of Alkaline Earth Oxides II. Analysis of Experimental Results for MgO, CaO, SrO, and BaO

Abstract The heat capacities of MgO, CaO, SrO and BaO, reported in part I have been analysed in terms of the frequency spectrum of the lattice with the assumption that the effect of anharmonicity of the lattice may be neglected for T ≦ (ΘD/3). Following the usual procedure the n-th moments of the frequency spectrum with n = - 3, -2, - 1, 0, 1 to 6 were calculated from the experimental data. From the low frequency expansion the apparent Debye characteristic temperature at 0 °K, Θ0, is calculated to be in good agreement with Θ0 (elast.), calculated from elasticity data. Also the limiting values at high temperatures,Θ∞, and the zero point energy, Ez, have been calculated. A comparison between the heat capacity data, the elastic constants and thermal properties of these oxides and the alkali-halides suggest that the interatomic forces of the alkaline-earth-oxides are rather similar to those of the alkaline fluorides. But no specific divalent character has been detected for these oxides. An appreciable anharmonic effect is present for all oxides.