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Isotope effect, Thermodynamic and Elastic properties of ZrCo and ZrCoH3: An ab-initio study

The intermetallic compound ZrCo and its hydrides are important materials for their use in hydrogen isotope storage. The dynamical, thermodynamic and elastic properties of ZrCo and its hydrides ZrCoX3 (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 ZrCoH3 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 ZrCoT3 > ZrCoD3 > ZrCoH3. The calculated formation energies of ZrCoX3, including the ZPE, are -146.7, -158.3 and -164.1 kJ/(mole of ZrCoX3) 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 ZrCoH3 are mechanically stable at ambient pressure. The Debye temperatures of both ZrCo and ZrCoH3 are determined using the calculated elastic moduli.