  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.
