Debye Temperature θD Research Articles

Structural, mechanical, and thermodynamic properties of Ni–Ti intermetallic compounds: First-principle calculation

Intermetallic compounds were applied widely in the fields of automotive and aerospace because of its excellent shape memory effect. In this work, the structural, mechanical, and thermodynamic properties of Ni–Ti intermetallic compounds are studied by first-principle calculation. The results show that Ti, NiTi3, NiTi2, NiTi, Ni4Ti3, Ni3Ti, Ni4Ti, and Ni are stable based on Born stable criterion. On the mechanical aspect, the bulk modulus of Ni–Ti intermetallic compounds increases with the rising electron density. Their ductility is ranked as follows: NiTi3 > Ni4Ti3 > NiTi2 > Ni4Ti > NiTi > Ni3Ti. And when the ratio of Ni and Ti is 3:1, it is the hardest. In addition, the Ni–Ti intermetallic compounds in this work are anisotropy, except NiTi2. On the thermodynamic aspect, the Debye temperature θD, melting point Tm, and minimum thermal conductivity kmin of Ni–Ti intermetallic compounds increase first and then decrease with the rising content of Ni. The θD and kmin of NiTi3 are the minimum among the Ni–Ti ICs mentioned above, and θD of Ni3Ti and kmin of NiTi are both the maximum. The melting point of Ni3Ti is 1940 K, it is the highest temperature.

Annealing temperature effect on structural, mechanical, and magnetic properties of Cd0.40M0.60ZnO2 (M = Mn, Ni) nanocomposites

We report here the effect of annealing temperature Tann (200–600 °C) on the structural, mechanical, and magnetic properties of Cd0.40M0.60ZnO2 (M = Mn, Ni) nanocomposites. The increase in Tann correlates with a significant change in unit cell volume (V), porosity (PS) crystallite size (Dhkl), particle size (r), Debye temperature (θD) and elastic modulus (Y). The values of V, r, θD and Y are higher for the Mn-series than Ni. While the values of PS and Dhkl are higher for Mn than Ni at Tann ≤ 300 °C, and the reverse is true at Tann ≥ 400 °C. The average particle size is 10.6 ± 2.4 nm for Mn-series, but it is decreased to 7.5 ± 4.0 nm for Ni-series, indicating quantum-dot size. Surprisingly, both series exhibit ferromagnetic behavior as Tann increases to 600 °C, but the magnetization parameters for the Mn series are higher than those for Ni. Furthermore, the anisotropy field (Ha) is about 350 times higher than the corrective field (Hc), indicating hard magnetic materials. The switching field distribution (SFD) is increased by annealing, but it is higher for Ni-series than Mn. The considered nanocomposites would be useful for altering plastic deformation and spintronic devices.

Anisotropy of elastic properties of cubic Nb3O3 niobium monoxide

The band structure calculation indicated that cubic Nb3O3 niobium monooxide is a com-pound with metallic conductivity. The anisotropy of the elastic properties of cubic (space group Pm3‾m) niobium monoxide Nb3O3 has been studied. The elastic stiffness constants cij for cubic Nb3O3 monoxide are computed using the density functional theory. The dependences of the Young's, bulk and shear moduli, as well as the Poisson's ratio in the (100), (110) and (111) planes of cubic niobium monoxide Nb3O3 on the crystallographic direction [hkl] are calculated. It is found that the maximum the Young's and shear moduli are observed in the [001], [010], and [100] directions, and the minimum values of the Young's and shear moduli are observed in the [±1 ± 1 ±1] directions of cubic niobium monoxide, respectively. Relatively small changes in the elastic characteristics of Nb3O3 depending on the [hkl] direction indicate a slight anisotropy of its elastic properties. Cubic niobium monoxide is mechanically and dynamically stable. The hardness HV and the Debye temperature θD of polycrystalline cubic niobium monoxide Nb3O3 are determined to be 17.2 GPa and ∼640 K, respectively.

The stability, electronic, thermal, and optical properties of silver halide (AgX: X = F, Cl, Br, and I) semiconductors: Ab-initio study

The structural properties, mechanical and dynamic stability, electronic, thermal and optical properties of silver halide AgX (X = F, Cl, Br, and I) compounds in the rock-salt phase within GGA and HSE approximations have been studied. The calculations are performed using the QUANTUM-ESPRESSO package which is based on the density functional theory (DFT) and the pseudo-potential method. The calculated elasticity parameters illustrated that the rock-salt phase complies with the mechanical stability conditions at ambient pressure. Based on the results of the mechanical calculations, it can be concluded that AgI is more rigid than other silver halide compounds, while the AgF compound is more malleable than other silver halide compounds. Also, against other examined silver halides, the AgI compound has an isotropic nature. The phonon scattering diagram has proved the dynamic stability of silver halide compounds in the studied rock-salt phase. Evaluation of the electronic results indicates that silver halide compounds in both GGA and HSE approximations have an indirect bandgap in the L−Γ path. In comparison to GGA, the HSE calculation improves the amount of bandgap toward a better agreement with experimental results. At room temperature, the hole mobility of silver halides is much less than the electron mobility. The decreasing trend of the effective mass of electrons in silver halides with the atomic radius of halide in the rock-salt phase leads to a faster carrier transfer rate in AgI, AgBr, AgCl, and AgF compounds, respectively. Moreover, by increasing the atomic radius of halide atom X, the Debye temperature θD and stiffness decrease, and inversely the heat capacity Cv increases. The increasing entropy relative to temperature refers to the endothermic properties of silver halide compounds. In both GGA and HSE approximations, the AgF compound has the highest absorption coefficient peak with the maximum optical absorption in the ultraviolet regime of the electromagnetic spectrum. The absorption coefficients of the silver halide compounds are of the order of 105 cm−1 which is comparable to the absorption coefficient of silicon crystals. The latter property along with a high stability and high electron mobility, makes silver halides attractive photocatalytic materials in the NaCl structure.

First principles study on the structural, electronic, and thermophysical properties of BiFeO3

Due to their special aspects and simple structure, perovskite structure materials are of enormous curiosity to scientists. Because of their ferroelectric, ferromagnetic, or ferroelastic properties, multiferroic materials could have interrelated electronic, magnetic, or structural order parameters. We represent the structural, electronic, and thermophysical properties in the ground state space group (221) of BiFeO3 according to Density Functional Theory (DFT). A BiFeO3 is investigated using Local Density Approximation (LDA) and Generalised Gradient Approximation (GGA) functional using ultrasoft pseudopotential. The present work calculated the structural, electronic, and thermophysical properties of BiFeO3 Perovskite. It demonstrates that the estimated structural properties of space group (221) BiFeO3 correspond well with existing research. The electronic attributes include band structure, total and projected density of states, electronic charge density, and Fermi surface topology. The thermophysical properties, like specific heat capacity, thermal expansion (α), Gruneisen parameter (γ), isothermal bulk modulus (B0), and Debye temperature (θD), were calculated in the temperature range of 0 K to 1073 K.

Synthesis of Sr-doped Ni0.5Zn0.5SrxFe2-xO4 and the study of its structural, mechanical, magnetic, and electrical properties for high-frequency applications

The solid-state reaction method has been used to mold the spinel Ni–Zn ferrites with doped strontium (Sr) [Ni0.5Zn0.5SrxFe2-xO4; x = 0.00, 0.01, 0.03, 0.05, and 0.10]. The powder X-ray diffraction approach was driven to investigate the crystal lattice of the studied samples. By using a variety of methods, including the Debye-Scherrer (D-S) formula, the Williamson-Hall (W–H), the Halder-Wagner (H–W), and the size-strain plot (SSP), where broadening of the XRD peaks are used, we have calculated the crystallographic features of Ni–Zn ferrites to ascertain the crystallite size and lattice strain. With doped Sr contents in samples, the lattice constants of the studied ferrites were decreased. Scanning electron microscopy (SEM) was used to analyze the sample's surface. Using the Image J software, the samples' grain size was calculated. We also performed the FTIR calculation, which confirmed that the ferrites we studied were spinel ferrites. The stiffness constants and elastic moduli were enumerated using the FTIR data to evaluate the mechanical behavior of the studied samples. Important thermal parameters such as Debye temperature (ΘD) and melting temperature (Tm) were also calculated. The magnetic behavior characterizing parameters have been analyzed via a vibrating sample magnetometer (VSM). Our studied samples are soft magnetic materials. We found the magnetic and electric losses to be negligible. Over a wide frequency extent, from 102 to 106 Hz at ambient temperature, an impedance analyzer was utilized to examine the samples' dielectric properties and AC resistivity. In the high-frequency region, the dielectric constant is frequency independent and the values of the dielectric constant are decreased with doped materials. Resistivity is increased with Sr-doped materials.

Theoretical investigation on the structural and vibrational properties of some alkali liquid metals: A pseudopotential approach

Along with a few elastic constants, a recently created pseudopotential is employed to examine the vibrational properties of some simple alkali metals, i.e. Li, Na, K, Rb and Cs. The phonon dispersion curves (PDC) are computed in the text. (ωL and ωT), longitudinal sound velocity (vl), transverse sound velocity (vt), isothermal bulk modulus (B), modulus of rigidity (G), Young’s modulus (Y ), Debye temperature (θD) of some liquid alkali metals. The second order technique used in the current work, using Hubbard and Beeby (HB) equations, is based on pseudopotential theory. The various Percus-Yevick hard sphere (PYHS) and one-component plasma (OCP) structure factors used in the current investigation are used to construct the pair correlation function g(r). The current paper makes use of three distinct forms of local field correction functions developed by Hartree (H), Taylor (T), and Nagy (N). The current findings are found to qualitatively agree with the experimental and theoretical data that is currently available.

Study the change of some physical and chemical properties of TiN under high pressure

The pressure equation of state of Titanium nitrate TiN was investigated in the current work using two equations of state (EOS) from the literature, including the Barden EOS and the Birch-Murnaghan EOS, whereas the Bardeen EOS, which is based on interstellar atomic potentials, and the Birch-Murnaghan EOS, which is based on the solid mechanics notion of finite strain. The EOSs were processed to identify the impacts of high pressure on the bulk modulus B, Debye temperature θD and lattice constant a, which are characterizations of TiN. Ultimately, a fair comparison of the current findings with the first principle approximation and the generalized gradient approximation approach was conducted, and a perfect agreement was found. It was demonstrated that TiN EOS can be used to calibrate high pressure for chemical compound TiN .

The electronic, mechanical and thermodynamic properties of Fe–N binary compounds under 330 GPa: First-principle calculations

The structural, elastic and thermodynamic properties of Fe–N binary compounds have been investigated using the first-principle calculation. Fe8N, Fe4N, Fe2N, Fe3N2 FeN and FeN2 have been optimized and calculated under 330 GPa. Their mechanical stability has been verified by Born stable criterion. Firstly, the content of N will not change the conductivity of Fe–N binary compounds. And when the proportion of Fe and N become 1: 2, the electrons will gather to Fermi's level. It may be concluded that light element N is able to change the electronic structure of Fe–N binary compounds from the results of electronic properties. Secondly, mechanical properties, including Young's modulus E, Poisson's ratio σ, B/G, anisotropy and Vickers hardness, are calculated by elastic constants. E and Vickers hardness decrease with the rising content of N in Fe–N compound. However, when N becomes the main element in Fe–N binary compound, the varying tendency change conversely. Particularly, Fe2N has the lowest E and Vickers hardness, approximately 902.90 GPa and 54 GPa respectively. On the contrary, the varying trend of σ is opposite, and Fe2N has the highest σ, 0.40. According to the B/G, Fe–N compound presents an excellent ductility, especially FeN2. Moreover, all of structures remains elastic anisotropy. Finally, thermodynamic properties, including Debye temperature θD and minimum thermal conductivity kmin, increase with the rising content of N in Fe–N binary compound. Ultimately, FeN has a lower Tm compared with pure Fe under inner core pressure. It means that adding N into Fe is able to decrease the Tm of pure Fe.

Anharmonicity effects and thermal expansion of thermoelectric (M,M’,M”)NiSn (M,M’,M”=Ti, Zr, Hf) half-Heusler alloys

High-resolution synchrotron radiation X-ray powder diffraction was used for the structural characterization of half-Heusler alloys with compositions MNiSn, M0.5M′0.5NiSn, and M0.5M′0.25M”0.25NiSn ((M, M′, M”) = Ti, Zr, Hf). These alloys were synthesized by arc melting and subsequent thermal annealing. Rietveld refinements of the room temperature patterns revealed that the unit cell parameter is larger for ZrNiSn and smaller for TiNiSn, in accordance with the respective atomic radii. The site occupation of each atomic species exhibited similar trends to those reported in the literature. The values of the linear coefficient of thermal expansion (α) for all the investigated phases within the alloys are < 10−5 K−1. In addition, the value of the Debye temperature (θD) is estimated by analyzing the temperature dependence of the isotropic atomic displacement parameters. In the case of these half-Heusler alloys, it is observed that a lower θD corresponds to a lower α. The good agreement between the temperature dependence of the Debye temperature and the calculated values using the Thirring-Stern expansion enables us to demonstrate the significant role of anharmonicity: the lighter the compound, the lower the anharmonicity. Furthermore, we also discuss the implications of anharmonicity on the thermal conductivity of this family of half-Heusler compounds at room temperature.

Electronic structure, thermodynamics, and thermoelectric properties of YxAl1−xN semiconductor alloys for new promising optoelectronics and energy conversion: Ab Initio study

Key characteristics such as structural, electronic, thermodynamic, and thermoelectric of wurtzite yttrium aluminum nitride (YxAl1−xN) semiconductor alloys (with 0≤ x ≤ 0.375) were investigated using Ab Initio density functional simulation within powerful full-potential linear augmented plane wave (FP‒LAPW) method. The equilibrium structural parameters (a0, c0, c0/a0,V0) were determined using the revised GGA−PBEsol approach in perfect agreement with experiments. The lattice a0-parameter varies almost linearly with yttrium concentration with a bowing of −0.08597 Å, while the c0-parameter has a bowing of −0.5715 Å. The lattice dynamics of doped YxAl1−xN systems were analyzed based on formation energy and phonon frequencies. Electronic structures of wurtzite YxAl1−xN described from a modern nKTB−mBJ potential show bandgap engineering with a range of [6.10 eV–3.85 eV] for x varies from 0 to 0.375, covering emission wavelengths [203 nm–322 nm] in the ultraviolet spectrum. The electron charge density contours indicate ionic bonding in wurtzite YxAl1−xN. Using the quasi-harmonic Debye model, thermodynamic properties of YxAl1−xN alloys, including volume (V0), mass modulus (B0), specific heat (Cv), thermal expansion (α), entropy (S), Debye temperature (ΘD) and Grüneisen parameter (γ), were calculated and analyzed under temperature and pressure effects. Moreover, electronic transport properties, such as the Seebeck coefficient (S), electrical conductivity (σ/τ), power factor, thermal conductivity (κel/τ), and figure of merit (ZT), of YxAl1−xN alloys were determined using BoltzTraP code. YxAl1−xN (at x = 0.25 and T = 600 K) exhibited the largest magnitude of S, with a value of ∼213.9 μV/K, and ZT ∼ 0.72. It also had the lowest value of κ/τ ∼9.9 × 1013 W m−1.K−1.s−1. Wurtzite YxAl1−xN crystal appears to be an extremely interesting candidate for potential applications in optoelectronics (UV) and future green energy system.

DFT prediction of the stability and physical properties of M2GaB (M = Sc, V, Nb, Ta)

This study explored the physical properties of MAX phase borides, M2GaB (M = Sc, V, Nb, Ta), aided by the density functional theory (DFT) for the first time. The optimized lattice constants were obtained by minimizing the total energy. We checked the thermodynamic stability by computing the formation energies. We calculated the electronic band structure, density of states (DOS), and charge density mapping to reveal the electronic ground state and bonding nature. The computed stiffness constants (Cij) confirmed the mechanical stability of the investigated compounds. Young's modulus, shear modulus, bulk modulus, and Poison's ratio have been computed using Cij. We calculated the Pugh's ratio, Poisson's ratio, and Cauchy pressure to judge the ductility/brittleness. The Vickers hardness values were calculated. The anisotropic properties of M2GaB compounds were studied by the elastic moduli's directional projections and the anisotropy indices' calculations. We have discussed the acoustic behavior of the M2GaB phases. We have also investigated the Grüneisen parameter, the Debye temperature ϴD, the thermal expansion coefficient, the specific heat, the Helmholtz free energy, the entropy, the internal energy, and the lattice thermal conductivity (Kph) of these borides. To determine the suitability as thermal barrier coating (TBC) materials or whether the compounds are appropriate for high-temperature applications, the minimum thermal conductivity (Kmin) and melting temperature (Tm) have also been calculated. The compounds' dynamical stability was examined using the phonon dispersion curves. The optical parameters have been studied, and it has been found that these compounds are compatible as coating materials to reduce solar heating.

Magnetothermal Properties and Magnetocaloric Effect in the 3d Ferromagnetic Elements: Fe, Co, and Ni

We present a calculation of magnetothermal properties and magnetocaloric effect (MCE) for the ferromagnetic elements: Fe, Co, and Ni. In particular, we calculated the temperature and field dependences of magnetization, heat capacity, entropy, isothermal entropy change Delta {S}_{m}, adiabatic temperature change ΔTad, and the two figures-of-merit: the relative cooling powers RCP(S) and RCP(T). We have used the mean-field theory in calculating the magnetization, magnetic heat capacity, and magnetic entropy. The lattice and electronic contributions to the total heat capacity and entropy were calculated using standard relations to subsequently calculate Delta {T}_{ad}. Those contributions depend on the Debye temperature ϴD and the coefficient of the electronic heat capacity γe respectively. The Maxwell relation is used to calculate Delta {S}_{m} and Delta {T}_{ad}. As an example of our results, the maximum Delta {S}_{m} for the three elements, in 6 T, is between 0.17 to 0.36 J/mol K and the maximum Delta {T}_{ad} mathrm{} is between 0.46 to 1.5 K/T for the same field change. The relative cooling power RCP(S) is in the 15–36 J/mol range for the three elements in a 6 T field. Also, the relative cooling power, RCP (T), is in the 162–1044 {K}^{2} range for the same field. For Fe and Co the RCP (T) per Tesla values, i.e., 139 and 174 {K}^{2}/T respectively are comparable to that of Gd and other Gd-based magnetocaloric materials. The behavior of the magnetization, magnetic heat capacity, and magnetic entropy shows that the phase transition in these three elements is of the second order. The universal curve and Arrott plots further support this conclusion.

Influence of vacancy on the elastic, thermodynamic and electronic properties of LaMgNi4 alloys from first-principles calculations

In this work, the structural stability, mechanical, electronic, and thermodynamic characteristics of LaMgNi4 alloys with different vacancies are discussed in detail. The calculated results of formation enthalpy (ΔH) of LaMgNi4 alloys with Mg-Va, Ni-Va2, La-Va1 and La-Va2 vacancies are −0.294eV/atom, −0.273eV/atom, −0.241eV/atom and −0.241eV/atom, respectively, and the results of phonon dispersion curves show that these vacancy models do not exhibit imaginary frequency in any high symmetry direction, which indicates that these models have stable structure. In addition, different vacancies have different effects on the mechanical properties of LaMgNi4 alloys. For example, the existence of Mg-Va, La-Va1, and La-Va2 vacancies enhances the mechanical properties of LaMgNi4 alloys, while the existence of Ni-Va2 vacancy weakens its mechanical properties. From the perspective of electronic structure, the change of mechanical properties of LaMgNi4 alloys is probably caused by the change of electronic state density at the Fermi level due to the existence of different vacancies. The thermodynamic properties such as the specific heat (Cv) and Debye temperature (ΘD) of the LaMgNi4 alloys with different vacancies are calculated by phonon calculations for wide temperature range from 0 K to 1000 K, and further discussed in detail. Finally, the adsorption of O atom on LaMgNi4 (110) surface and the elastic constants and the elastic modulus of random solid solution alloys of La4Mg4Ni14Cu2 are also investigated.

Tailoring the hydrogenated mechanism of Pt3Al from first-principles investigation

Pt–Al compounds are promising high-temperature structural materials. However, the hydrogenated behavior of Pt3Al is still unclear. To explore the hydrogenated mechanism, we apply the first-principles method to investigate the role of hydrogen (H) in Pt3Al. Here, the cubic and tetragonal Pt3Al are considered. Based on the hydrogen occupied position, three H-doped sites are designed in cubic and tetragonal phases. It is found that the hydrogen is a thermodynamic stability in two Pt3Al phases. Compared to the cubic Pt3Al, the hydrogen prefers to occupy the octahedral interstice (H(2) site) of the tetragonal Pt3Al. Importantly, the H-doped Pt3Al is a mechanical stability. In particular, it is found that the hydrogen weakens the volume deformation resistance, shear deformation resistance and elastic stiffness of Pt3Al. But the hydrogen improves the ductility of Pt3Al due to the electronic interaction between hydrogen and Pt3Al. Naturally, the low elastic properties are that the introduction of hydrogen weakens the localized hybridization between Pt atom and Al atom, and forms the H–Pt bond. In addition, the hydrogen also weakens the Debye temperature (θD) of Pt3Al.

Effects of Fe occupancy on physical properties of non-magnetic GeGa2O4 spinel oxide

This study investigated the structural, elastic, electronic, thermal, magnetic, and optical behavior of GeGa2O4, FeGa2O4, GeFe2O4, and FeFe2O4 spinel oxides based on ab-initio calculations. The results showed that the non-magnetic spinel oxide GeGa2O4 exhibited remarkable physical properties due to Fe occupancy at different lattice sites within the spinel lattice. The Fe containing spinel oxides (FeGa2O4, GeFe2O4, and FeFe2O4) were found to be stable in the magnetic phase in contrast to the host GeGa2O4 spinel oxide. The spin polarizations of FeGa2O4, GeFe2O4, and FeFe2O4 oxides were calculated as 98.5%, 98.4%, and 100%, respectively. Analysis of the elastic and mechanical properties showed that all of the spinel oxides followed the Born and Huang criteria for mechanical stability. The highest Debye temperature (θD = 663.77 K) was determined for the FeGa2O4 spinel oxide. For GeGa2O4, FeGa2O4, GeFe2O4, and FeFe2O4 oxides, the calculated structural parameters (cation–anion bond lengths and average values of tetrahedral and octahedral radii) predicted the following cation distributions among the A and B atomic sites: (Ge2+)[Ga23+]O4−2, (Fe2+)[Ga23+]O4−2, (Ge4+)[Fe22+]O4−2, and (Fe+2)[Fe23+]O4−2. The calculated electronic structures indicated that the host GeGa2O4 spinel oxide and FeFe2O4 spinel ferrite were semi-conducting and half-metallic ferromagnetic, respectively, whereas FeGa2O4 and GeFe2O4 oxides exhibited semi-metallic behavior. The GeFe2O4 spinel oxide was found to have the highest saturation magnetization (185.79 emu g−1) and total magnetic moment (8.26 ΣBfu−1). The calculated optical properties indicated the suitability of these oxides for use in optical filters and sensors. The electronic and magnetic characteristics of these spinel oxides with excellent thermal and elastic stability suggest that they have potential uses in diluted magnetic semiconductor devices.

Promising high temperature thermoelectric performance of layered oxypnictide YZnAsO

Thermoelectric materials can convert heat into electricity directly via the Seebeck effect, providing an alternative to global energy demands. Here we present mechanical, dynamical, and thermoelectric properties of YZnAsO, a quaternary oxypnictide, in the framework of Density Functional Theory. The low value of Debye temperature (θD=308.29K) and high value of the Grüneisen parameter (∼1.77) hint for low lattice thermal conductivity (kl), and this is supported by the computed value of ∼0.4 W/mK at 800 K. The electronic transport coefficients are computed using Boltzmann transport equation beyond the constant relaxation time approximation (CRTA) including different scattering mechanisms. While the power factor for hole doping is higher along ‘a’, the kl is extremely low along ‘c’, resulting in a high figure of merit (ZT) along ‘c’. Hence, we predict YZnAsO as a promising n-type oxide thermoelectric owing to its low kl with a high ZT =1.07 at 800 K with 15% maximum thermoelectric efficiency.

Effect of annealing temperature on structural, optical and magnetic properties of Cd1-xMnxZnO2 nanocomposites: An investigation for ferromagnetic

The structural, optical, and magnetic qualities of Cd1-xMnxZnO2 nanocomposites with (0.00 ≤ x ≤ 1.00) are investigated and the paramagnetic ferromagnetic transition is explained. Two series (effect of annealing and composition) were synthesized using the hydrothermal method and then annealed for 3 h at annealing temperatures (Tann) of 400 °C or 600 °C. It is found that an increase in either x or Tann correlates with significant change in unit cell volume (V), crystallite size (Dhkl), Debye temperature (θD) and energy gap (Eg). Further, the samples at x = 0.60 show a sudden change or inflection point in the behavior of these parameters is detected. Furthermore, the values of Eg and Dhkl for the x = 0.60 sample are independent of the chosen Tann. The weight percent of oxygen increased as x increased, as well as it was higher at 600 °C than at 400 °C. The value of Dhkl at x = 0.40 was increased by increasing Tann from 20.7 nm to 26.3 nm. Surprisingly, both series of samples exhibit weak paramagnetic properties as x increases to 0.40. However, increasing x to 0.60 yields a strong ferromagnetic signature for both series as well as unusual unsaturated magnetizations of 4.20 and 1.25 emu/g. However, with a larger further than of x above 0.60, the behavior returns to a strong paramagnetic behavior, but with a small percentage of residual hysteresis. These novel outcomes open the way for a possible mechanism for room temperature ferromagnetic (RTFM) and strongly recommend the use of Cd1-xMnxZnO2 nanocomposites, for magnetic imaging, and spintronic devices.

Effect of cation distribution on structural and mechanical properties of Y3+ substituted Co-Zn spinel ferrites nanoparticles.

Yttrium (Y3+) substituted Co-Zn spinel ferrite nanoparticles with compositional formula Co0.9Zn0.2YxFe1.9-xO4 (x = 0.0, 0.015, 0.030, 0.045, 0.06) were synthesized by using sol-gel auto-ignition route. The structural and mechanical properties of Co-Zn ferrites were tailored by the replacement of Fe3+ ions by Y3+ ions. Rietveld refined X-ray diffraction patterns of all the samples confirm the cubic spinel structure. Lattice parameter increases with the substitution of Y3+ ions which may be due to the difference in ionic radii. The crystallite size obtained from XRD analysis is found in the nanometer range of 16.8 – 24.7 nm. Distribution of cations over tetrahedral – A and octahedral – B sites have been studied by using X-ray diffraction data and it is found that Y3+ ions prefers the octahedral – B site. Infrared spectra of all the samples were recorded in the wave number range of 300 cm−1 to 800 cm−1 which shows splitting of the two fundamental absorption bands. Two absorption bands (ν1 and ν2) observed in the range 380 – 610 cm−1 are belongs to tetrahedral – A and octahedral – B interstitial sites. The force constants (KO and Kt) and corresponding elastic parameters were determined by using IR data. The stiffness constant (C11), Young’s modulus (E), rigidity modulus (G), bulk modulus (B) and Debye temperature (θD) were found increases with the addition of Y3+ ions.

First-principles calculations of Mg2FeH6 under high pressures and hydrogen storage properties.

We report on structural properties, elastic constants, mechanical and dynamical stabilities, electronic band structure, and hydrogen storage applications of Mg2FeH6 at zero and high-pressure effects. The work has been realized within the full-potential linearized augmented plane wave method. At zero pressure, the material under study is stable and has a ductile nature. The electronic structure of the material of interest is determined to be X-X wide direct band gap semiconductor with an energy of 1.88eV. The hydrogen storage capacity wt (%) and the hydrogen desorption temperature are reported as 5.473 and 625.47K respectively. The Debye temperature ϴD is recorded as 698K using the elastic constants and about 775K using the Gibbs calculations. Under high-pressure effect up to 80GPa, the semiconductor still be an X-X semiconductor with an energy gap of 3.91eV. The Debye temperature ϴD increases monotonically up to about 1120K at 80GPa when using the calculated elastic constants whereas the desorption temperature decreases from 650 to 0K by increasing pressure from 0 to about 87GPa.