Structural, electronic, elastic and thermodynamic properties of hydrogen storage magnesium-based ternary hydrides

In this study, new, lightweight perovskite type hydrides; MgNiH3 (GHD is calculated as ~3.51 wt%) and MgCuH3 (GHD is calculated as ~3.32 wt%) are investigated. Hydrogen storage, structural, elastic, mechanical, electronic and thermodynamic behaviour of these hydrides are investigated using first principle calculations as a tool. Our elastic and mechanical analysis revealed that these hydrides are mechanically stable and have a ductile nature which is a necessary assessment required for handling materials for transportation. Furthermore, electronic band structures of hydrides indicate metallic characteristics for both hydrides. Many unknown thermodynamic properties of these ternary hydrides are revealed and discussed. © 2020 Elsevier B.V

Investigation of mechanical properties of KCaH3 and KSrH3 orthorhombic perovskite hydrides under high pressure for hydrogen storage applications

First principles calculations have been adopted to explore ground-state and high-pressure properties of KCaH3 and KSrH3 orthorhombic perovskite hydrides for the purpose of solid-state hydrogen storage. Formation enthalpies of materials, structural and mechanical properties, electronic and hydrogen storage properties are computed and examined. The computed formation enthalpies and phonon frequencies of KCaH3 and KSrH3 indicate dynamical stability at 0 GPa. The gravimetric hydrogen densities of KCaH3 and KSrH3 are found to be 3.55 wt% and 2.28 wt%, respectively. Also, the hydrogen desorption temperatures are calculated as 449 K and 394 K for KCaH3 and KSrH3. Elastic constants for each phase and several parameters derived from elastic constants are computed and evaluated, such as bulk and Shear modulus. The B/G ratios of materials depict that both KCaH3 and KSrH3 are brittle materials. The electronic properties show band gaps for both materials at 0 GPa, confirming an insulating nature and as pressure increases the band gap shrinks for KCaH3 and disappears for KSrH

Mechanical, electronic, thermodynamic and vibrational properties of X2MgAl (X = Sc, Ti and Y) from first principles calculations

Due to growing interest to predict and design new potential Heusler alloys by using theoretical calculations and highly functional software, research on Heusler alloys has taken great attention. From this point of view, this study considers investigation of X2MgAl (X = Sc, Ti and Y) alloys by adopting first principles calculations for the first time. A thorough investigation has been carried out to reveal these alloys' mechanical, electronic, vibrational and thermodynamic properties. It is seen that all alloys have negative formation energies as -0.278 eV/atom for Sc2MgAl, -0.058 eV/atom for Ti2MgAl and -0.304 eV/atom for Y2MgAl which indicates synthesisability and thermodynamic stability. Mechanical stability investigations based on the elastic constants of alloys have revealed that all alloys are mechanically stable. The electronic band structures of alloys demonstrate that X2MgAl (X = Sc, Ti and Y) alloys are metallic since there is no energy gap near the Fermi level. Cauchy's pressures of alloys are found as -17.791 GPa for Sc2MgAl, 31.404 GPa for Ti2MgAl and -11.759 GPa for Y2MgAl which displays that Sc2MgAl and Y2MgAl are brittle and Ti2MgAl is ductile. The phonon dispersion curves are calculated along the lines of high symmetry within the first Brillouin region. Phonon frequencies are completely positive in the full Brillouin region, which proves the dynamic stability of the L2(1) phases of these alloys. Several thermodynamic properties such as Debye entropy, temperature and vibrational free energy are also computed and analysed. Debye entropies of alloys follow Ti2MgAl > Y2MgAl > Sc2MgAl relationship

Ab-initio study of structural, electronic, elastic, phonon properties, and phase transition path of sodium selenite

The effects of pressure on structural, elastic, electronic, and vibrational properties of NaSe are studied using the SIESTA method. The dimensionless ratio, bulk modulus, elastic constants, Shear and Young modulus, and Poisson‘s ration are obtained for each phase. NaSe shows phase transitions from the P63/mmc phase (T = 0 K, P = 0) to the Cmcm phase at 10 GPa and from this phase to the Pmmm phase at 22 GPa. High pressure results in an improvement in resistance towards volume and shape change. Elastic constants evaluation indicates that the P63/mmc phase and the Cmcm phase of NaSe is mechanically stable. The B/G ratios of NaSe phases are also examined. It is found that NaSe has great ductility, however as pressure increases the ductility of NaSe decreases. Electronic and vibrational computation and analysis reveal that the P63/mmc phase and the Cmcm phase of NaSe demonstrate metallic character and both phases are dynamically stable. © 2020 Elsevier B.V

Modelling of water transport through mixed-ion conducting dense ceramics

WOS: 000434365200020This study develops and demonstrates a model that characterizes defect transports, responsible for water transport within dense ceramics, and calculates the diffusion coefficients for those defects. The multi-species mass transfer processes within yttrium doped barium cerates are modelled by applying the Nernst-Planck equation to the system. The Nernst-Planck equation with suitable boundary conditions is adopted to compute defect diffusion coefficients in COMSOL Multiphysics. All related equations, based on charge and defect conservation, are solved numerically and validated experimentally. The model also predicts the concentration distribution of the defects and potential profiles throughout the membranes. The results provided convenient insights about the water transport and charge distribution as a function of membrane thickness.Ministry of National Education TurkeyMinistry of National Education - TurkeyThe authors would like to acknowledge the Ministry of National Education Turkey for funding. Also, we would like to thank Prof. Ian Metcalfe for the useful discussions and School of Chemical Engineering, Newcastle University, UK for the university"s resources

Density functional theory investigation on structural, mechanical, electronic and vibrational properties of Heusler alloys AlXIr2 (X = Co, Cr, Cu, Fe and Zn)

This study focuses on the detailed investigation of full-Heusler AlXIr2 (X = Co, Cr, Cu, Fe and Zn) alloys. A first -principal plane-wave pseudopotential method based on density functional theory is adopted. The quantum -espresso package combined with the generalized gradient approach is used to reveal the structural, electronic, magnetic, mechanical and lattice dynamic properties of full-Heusler AlXIr2 (X = Co, Cr, Cu, Fe and Zn) alloys. The elastic constants are used to determine elastic stabilities of alloys based on Born criteria. The analysis showed that all alloys are elastically stable. Further detailed analysis has been carried out to reveal mechanical properties. It is found that all alloys are ductile and anisotropic. The electronic band structures are also obtained. All alloys except for AlCrIr2 are found to be metallic. AlCrIr2 has half-metallic nature. In addition, AlCrIr2, AlFeIr2 and AlCoIr2 has shown magnetic properties. The phonon spectra and density of states are investigated to examine dynamical stability. It is seen that all alloys exhibit dynamical stability due to having positive phonon frequencies

Structural evolution, mechanical, electronic and vibrational properties of high capacity hydrogen storage TiH4

Titanium tetra hydride is considered for hydrogen storage purposes. Firstly, formation energy, hydrogen desorption temperature and gravimetric hydrogen density of TiH4 is computed. Secondly, an ab initio constant pressure molecular dynamic simulation under pressure is performed to reveal behaviour of TiH4 for the first time. The result exhibits two phase transitions successively. C2/m phase of TiH4 transforms into C2/c phase at 40 GPa simulation pressure. Then, elastic constants of phases are determined to examine mechanical stability of phases. Based on the evolution of elastic constants, it is found that C2/m phase fulfils Born stability criteria for a monoclinic structure, indicating that C2/m phase is mechanically stable whereas C2/c phase is not mechanically stable. Additionally, several critical parameters which are important for hydrogen storage such as brittleness and ductility, Young and Shear modulus are obtained and analysed. In addition, electronic structures of phases are calculated and evaluated. Finally, dynamic stability from phonon dispersion curves is examined. C2/m phase is also found to be dynamically stable. © 2020 Hydrogen Energy Publications LL

Investigation and evaluation of water permeation through BaCe0.8Y0.2O3-d electrolyte for solid oxide fuel cells

PhD ThesisMinistry National Education Turke

The productivity gap: Monetary policy, the subprime boom, and the post-2001 productivity surge

It is widely believed that, in the wake of the dot.com crash, the Fed kept the federal funds target rate too low for too long, inadvertently contributing to the subprime boom. We attribute this and other Fed departures from a “neutral” policy stance to the Fed's failure to respond appropriately to exceptional rates of total factor productivity growth. We then show how the Fed, by adhering to a nominal GDP growth rate target, might have succeeded in maintaining such a neutral stance.pre-prin