EFFECT OF HYDROGEN ABSORPTION ON STRUCTURE, SUPERCONDUCTIVITY, MAGNETIC-SUSCEPTIBILITY AND HEAT-CAPACITY OF ZR2RH

The superconducting intermetallic compound Zr2Rh (CuAl2-type C16 tetra gonal structure with T(c) almost-equal-to 11 K) can be hydrided at roo m temperature and about 1 atm hydrogen pressure to give a composition Zr2RhHx (x = 4.25 +/- 0.25) without a change in crystal structure. Thi s 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 o n the hydride phase and compared with those of the parent compound. It is found that: (i) Zr2RhH4.25 exhibits metallic behaviour similar to Zr2Rh; however, no superconducting transition is seen down to 1.8 K; ( ii) the hydride is Pauli paramagnetic, but its susceptibility is reduc ed to almost one-half of the value of the parent compound; (iii) the D ebye temperature of the hydride is almost twice that of Zr2Rh, indicat ing stronger bonding despite the increased interatomic separation; (iv ) the electronic specific heat coefficient is reduced by almost an ord er of magnitude on hydriding. Approximate estimates of the density of states at the Fermi level and the electron-phonon coupling constant ha ve been obtained for the intermetallic compound and the hydride.