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Uranium silicide compound is a promising candidate as low enriched uranium nuclear fuel in light water reactors. Here we report a comprehensive study on structural, electronic, elastic, vibrational and thermodynamic properties of U 3 Si 2 using plane wave based density functional theory. The electron-ion interaction and exchange-correlation energy terms have been described by projected-augmented wave method and generalized gradient approximation scheme, respectively. The relativistic corrections to the total energy have been accounted by incorporating the spin-orbit interactions in the total energy calculations. The results showed good agreement between the experimental and theoretical lattice parameters. The electronic structure of U 3 Si 2 compound suggests significant contribution from the 5 f and 3 p orbitals of U and Si atoms at the Fermi energy level, respectively. The formation energy (Δ f H ) of U 3 Si 2 at 0 K, after zero point energy correction, have been estimated to be −37.40 kJ/mol. Elastic property calculation of U 3 Si 2 showed mechanical stability and anisotropy at ambient pressure. In addition, the phonon calculation showed that U 3 Si 2 is dynamically unstable. The temperature dependent thermodynamic properties of U 3 Si 2 have also been evaluated using the phonon density of states. [ABSTRACT FROM AUTHOR]

With increasing demand for hydrogen economy driven world, the fundamental research of hydrogen-metal interactions has gained momentum. In this work we report a systematic theoretical study of the stability of different surfaces of intermetallic ZrCo that is a possible candidate as a getter bed for tritium. Our first principles ab initio thermodynamic calculations predict that amongst the (100), (110) and (111) surfaces, the stoichiometric (110) surface is the most stable one over a wide range of Co chemical potential. We have also studied adsorption, dissociation and diffusion of hydrogen on the (110) surface. On the basis of total energy, it is seen that adsorption of molecular hydrogen (H 2 ) on the surface is much weaker than atomic hydrogen. The H 2 decomposition on ZrCo surface can easily take place and the dissociation barrier is calculated to be 0.70 eV. The strength of binding of H atom on the surface is more or less independent of surface coverage till 1.0 ML of H. The thermodynamic stability of atomic H adsorbed on the surface, in subsurface and bulk decreases from surface to bulk to subsurface. Though the H atoms are mobile on the surface, their diffusion to the subsurface involves a barrier of about 0.79 eV. [ABSTRACT FROM AUTHOR]

Zirconium based alloys have potential applications in automobile, energy and spacecraft industries. The structural, electronic, elastic, vibrational and thermodynamic properties of orthorhombic ZrNi and ZrNiH 3 are studied in detail using the projector augmented wave method and the generalized gradient approximation based on density functional theory. The optimized lattice parameters of both ZrNi and ZrNiH 3 agree well within ±1% from the experimental values. The electronic structure analysis shows significant contribution of 4 d and 3 d orbitals of Zr and Ni to the fermi energy level, respectively and along with signatures of two types of hydrogen atoms occupying the lattice of ZrNiH 3 . Elastic property calculation of these two compounds showed mechanical stability and anisotropy at ambient pressure. In addition, the phonon calculation of both the compounds showed that ZrNi is dynamically stable but ZrNiH 3 is dynamically unstable. The formation energies (Δ f H ) of ZrNi and ZrNiH 3 at 0 K, after zero point energy correction, have been estimated to be −41.87 kJ/mol and −78.25 kJ/mol H 2 , respectively. The temperature dependent thermodynamic functions of ZrNi and ZrNiH 3 have also been calculated from the Debye-Grüneisen quasi-harmonic approximation. [ABSTRACT FROM AUTHOR]

The thermodynamic properties of ZrCo intermetallic were investigated both experimentally and theoretically to determine its applicability for the storage of hydrogen isotopes. The enthalpy increments of ZrCo were measured using a high temperature inverse drop calorimeter in the temperature range 642–1497 K. The enthalpy increments and heat capacity obtained for Zr 0.5 Co 0.5 (s) in the temperature range 642–1497 K were fitted into following polynomial expressions: H m 0 ( T ) − H m 0 ( 298.15       K ) ( J · m o l − 1 ) = 25.682 · ( T K ) + 29.807 · 10 − 4 · ( T K ) 2 + 2.1864 · 10 5 · ( K T ) − 8655.5 C p . m 0 ( J · K − 1 · m o l − 1 ) = 25.682 + 5.961 · 10 − 3 · ( T K ) − 2.1864 · 10 5 · ( K T ) 2 The enthalpy of formation of ZrCo(s) at 298.15 K was calculated to be −55.96 kJ mol −1 using the ab-initio method. The temperature dependent thermodynamic functions were calculated from the Debye–Grüneisen quasi-harmonic approximation. A set of thermodynamic functions for ZrCo alloy were also calculated using experimental heat capacity data obtained in this study. The theoretically calculated low temperature heat capacity ( C p , m 0 ) and entropy ( S m 0 ) values of ZrCo smoothly joined with that of experimental high temperature data. [ABSTRACT FROM AUTHOR]

The dynamical, thermodynamic and elastic properties of ZrCo and its hydrides ZrCoX 3 (X = H, D and T) are reported. While the electronic structure calculations are performed using plane wave pseudopotential approach, the effect of isotopes on the vibrational and thermodynamic properties has been demonstrated through frozen phonon approach. The results reveal significant difference between the ZrCoH 3 and its isotopic analogs in terms of phonon frequencies and zero point energies. For example, the energy gap between optical and acoustic modes reduces in the order of ZrCoT 3 > ZrCoD 3 > ZrCoH 3 . The vibrational properties shows that the intermetallic ZrCo is dynamically stable whereas ZrCoX 3 (X = H, D and T) are dynamically unstable. The calculated formation energies of ZrCoX 3 , including the ZPE, are −146.7, −158.3 and −164.1 kJ/(mole of ZrCoX 3 ) for X = H, D and T, respectively. In addition, the changes in elastic properties of ZrCo upon hydrogenation have also been investigated. The results show that both ZrCo and ZrCoH 3 are mechanically stable at ambient pressure. The Debye temperatures of both ZrCo and ZrCoH 3 are determined using the calculated elastic moduli. [ABSTRACT FROM AUTHOR]

The structural, electronic, elastic and thermodynamic properties of Laves phase alloy Zr 2 Fe and its hydride Zr 2 FeH 5 were investigated employing the state of the art first principles calculation. The equilibrium structures of both Zr 2 Fe and Zr 2 FeH 5 were found to be within ±1% from the experimental values. The charge distribution and bonding between the constituent atoms of Zr 2 Fe and Zr 2 FeH 5 were examined through electronic density of state spectra, charge density contour, and electron localization function analysis. The density of states showed significant contribution of 4d and 3d orbitals of Zr and Fe to the Fermi energy level, respectively and signatures of two types of hydrogen atoms occupying the lattice of Zr 2 FeH 5 . Investigation of elastic properties showed that two compounds were mechanically stable and anisotropic. The formation energy (Δ f H ) of Zr 2 Fe and Zr 2 FeH 5 at 0 K, after zero point energy correction, was estimated to be −40.04 kJ/mol and −147.40 kJ/mol H 2 , respectively. A van’t Hoff plot was constructed using computed thermodynamic functions of Zr 2 Fe and Zr 2 FeH 5 . [ABSTRACT FROM AUTHOR]

Abstract: The Zr–H system is of particular importance for the solid state storage of hydrogen isotopes in the form of zirconium hydride. Here we report the structural, electronic, vibrational and thermodynamic properties of ZrH2, ZrD2 and ZrT2 using density functional theory (DFT). The structural optimization was carried out by the plane-wave based pseudo-potential method under the generalized gradient approximation (GGA) scheme. The electronic structure of the ZrH2 compound was illustrated explicitly. The vibrational, thermodynamic, and the effect of isotopes on ZrX2 (X = H, D, T) compounds were evaluated by the frozen phonon method. Both the Raman and infrared active vibrational modes of ZrX2 at Γ-point showed significant isotopic effect on ZrX2 compounds. For example, the phonon energy gap between optical and acoustic modes reduces for ZrT2 than ZrD2 and ZrH2. The formation energies of ZrX2 compounds, including the ZPE contributions, were estimated to be −143.68, −147.87 and −150.01 kJ/(mole of compound) for X = H, D and T, respectively. [Copyright &y& Elsevier]

This study investigated thermodynamic properties of uranium-titanium alloy to determine its suitability for storage of hydrogen isotopes. The enthalpy increments of UTi were measured using a high temperature inverse drop calorimeter in the temperature range of 299-1,169 K. Temperature dependence of the molar enthalpy increment and molar heat capacity is expressed in the form $$ H^\circ_{\text{m}} (T) - H^\circ_{\text{m}} (298.15\,{\text{K}})({\text{J }}\,{\text{mol}}^{ - 1} ) = 23.236(T/{\text{K}}) + 53.292 \times 10^{ - 3} (T/{\text{K}})^{2} - 21.294 \times 10^{5} ({\text{K}}/T) - 4523 $$ and $$ C^\circ_{\text{p,m}} ({\text{J}}\,{\text{K}}^{ - 1} \,{\text{g}}^{ - 1} ) = 23.236 + 10.6584 \times 10^{ - 2} (T/{\text{K}}) + 21.294 \times 10^{5} ({\text{K}}/T)^{2} (300 \le T/{\text{K}} \le 900) $$, respectively. A set of self consistent thermodynamic functions such as entropy, Gibbs energy function, heat capacity, and Gibbs energy and enthalpy values for UTi have been computed using data obtained in this study and required data from the literature. [ABSTRACT FROM AUTHOR]

Abstract: The ZrCo intermetallic is considered to be strategically important for hydrogen isotope storage and its use in the International Thermonuclear Experimental Reactor (ITER) system. Here we report the structural, electronic and thermodynamic properties of ZrCo and ZrCoH3 using the first-principles approach. The calculations are performed using a plane-wave based pseudo-potential approach under the framework of spin-polarized density-functional theory. The ground state properties like lattice constants, bulk moduli, and enthalpy of formation have been determined by optimizing the atomic and electronic structure of ZrCo and ZrCoH3 compounds. From the total energy calculations, the enthalpy of formation of ZrCoH3 from ZrCo is estimated to be −91 kJ/mol H2 at 0 K. Both lattice parameters and formation energy are found to be in good agreement with their corresponding experimental values. The nature of chemical bonding in ZrCo and ZrCoH3 has been analyzed from the electronic density of states spectrum of the constituent materials. [Copyright &y& Elsevier]

Abstract: Using the state of the art first principles calculation, we report the structural, electronic, and thermodynamic properties of U2Ti, U, and Ti. All calculations have been performed using a plane wave (PW) based pseudopotential method under the framework of spin polarized density functional theory. The electron–ion interaction and the exchange correlation energy are described using the projector-augmented wave (PAW) method and the generalized gradient approximation (GGA) scheme, respectively. The effect of the relativistic spin–orbit interaction on these properties has been investigated. The results are analyzed to obtain the structural parameters, lattice constants, bulk moduli, electronic specific heat, and the compound formation energy. On the basis of energetics, the formation energy (Δf H at 0K) of U2Ti compound is estimated to be −30.84kJ/mol. A satisfactory agreement between the present investigation and available experimental data demonstrates the applicability of PW based PAW approach for such systems. Further, the nature of chemical bonding between U and Ti atoms in the U2Ti is illustrated by comparing their electronic density of state spectrum. [Copyright &y& Elsevier]