Density functional study of vibrational, thermodynamic and elastic properties of ZrCo and ZrCoX3 (XÂ =Â H, D and T) compounds

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 vibrational properties shows that the intermetallic ZrCo is dynamically stable whereas ZrCoX3 (X = H, D and T) are dynamically unstable. 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.