Insight into Phase Stability in the Mg-Pd System: The Ab Initio Calculations
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Insight into Phase Stability in the Mg-Pd System: The Ab Initio Calculations Wojciech Gierlotka1 • Adam De˛bski2 • Sylwia Terlicka2 • Władysław Ga˛sior2 Magda Pe˛ska3 • Marek Polan´ski3
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Submitted: 8 June 2020 / in revised form: 2 July 2020 ASM International 2020
Abstract Thermodynamic properties of all reported up to date intermetallic phases in Mg-Pd equilibrium system are reported in this work. Ab initio method was applied to calculate formation energies, relaxed lattice constants and bulk moduli. The consistent set of data was obtained, including formation energies and bulk moduli of Mg6Pd and Mg9Pd11 that were calculated for the first time. The obtained energies of formation can be used for future thermodynamic optimization of promising hydrogen storage material Mg-Pd. Keywords ab initio calculations intermetallics magnesium alloys thermodynamics
for materials currently applied in hydrogen technology. Magnesium palladium alloys are within the interest of researchers due to their well-known ability to interact with hydrogen[1] being in the same time cheaper than pure palladium or platinum. Unfortunately, a phase diagram of the Mg-Pd system that is necessary for understanding of phase stability, phase equilibrium, and phase transformations does not have a mathematical model yet due to the lack of thermodynamic information that is necessary for numerical modeling. In order to fill that gap, it was decided to calculate formation energies of all intermetallic compounds (IMC) reported in literature of Mg-Pd system[2] using Density Functional Theory (DFT).[3]
2 Technique 1 Introduction Hydrogen is still considered as a fuel of the future, but its practical application requires effective storage, detection and catalysts for its splitting in fuel cells. By these reasons, the mechanisms of its interaction with different materials, including precious metals and their alloys, are still being investigated to find cheaper and more effective substitutes
& Wojciech Gierlotka [email protected] 1
Materials Science and Engineering Department, National Dong Hwa University, Hualien, Taiwan
2
Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 25 Reymonta Street, 30-059 Krako´w, Poland
3
Military University of Technology, 2 Kaliskiego Street, 00-908 Warsaw, Poland
The calculations were done by ab initio method within the DFT that was implemented in Quantum Espresso.[4] The calculation used General Gradient Approximation pseudopotential functional parameterized by Padrew, Burke, and Ernzerhof revised for solids approach (GGA BPESol).[5] For all the calculation cut-off energies and k-point dis˚ , respectively. Before tance were set to 680 eV and 0.20 1/A performing the final calculation, the convergence test with respect to cut-off energy and k-point density was done. The structures of all phases were taken from the Crystallography Open Database.[6] During the calculation, structures were fully relaxed using Broyden–Fletcher–Goldfarb– Shanno (BFGS) algorithm with the convergence thresh
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