Effect of hydrogen absorption on structure, superconductivity, magnetic susceptibility and heat capacity of Zr2Rh

Abstract The superconducting intermetallic compound Zr 2 Rh (CuAl 2 -type C16 tetragonal structure with T c ≈ 11 K) can be hydrided at room temperature and about 1 atm hydrogen pressure to give a composition Zr 2 RhH x ( x = 4.25 ± 0.25) without a change in crystal structure. This is the first report on the stabilization of a hydride phase with an appreciable hydrogen content. Results of X-ray diffraction, electrical resistivity, magnetic susceptibility and heat capacity are reported on the hydride phase and compared with those of the parent compound. It is found that: (i) Zr 2 RhH 4.25 exhibits metallic behaviour similar to Zr 2 Rh; however, no superconducting transition is seen down to 1.8 K; (ii) the hydride is Pauli paramagnetic, but its susceptibility is reduced to almost one-half of the value of the parent compound; (iii) the Debye temperature of the hydride is almost twice that of Zr 2 Rh, indicating stronger bonding despite the increased interatomic separation; (iv) the electronic specific heat coefficient is reduced by almost an order of magnitude on hydriding. Approximate estimates of the density of states at the Fermi level and the electron-phonon coupling constant have been obtained for the intermetallic compound and the hydride.