Thermodynamic and Magnetic Properties of Pd<SUB>0.93</SUB>Ag<SUB>0.07</SUB> Hydride

Abstract

Thermodynamic and magnetic properties of the Pd 0.93 Ag 0.07 hydrides were measured. The isotherms of Pd 0.93 Ag 0.07 -H and -D systems in the temperature range 373-523 K showed the plateau regions to be within 0.05 < [Q (Q = H or D)]/[Pd 0.93 Ag 0.07 ] < 0.4. From an investigation of the thermodynamic isotope effect for the formation and decomposition of hydride, the enthalpy changes, ΔH° β→α , for desorption of hydrogen and deuterium were evaluated to be 43.0 kJ/mol H2 and 36.4 kJ/mol D2 , respectively. It was observed that the magnetization of Pd 0.93 Ag 0.07 Hx at ambient temperature increased with increasing magnetic field. Since the magnetization was not saturated up to 7 T, it can be concluded that Pd 0.93 Ag 0.07 H x is paramagnetic. The magnetic susceptibility of Pd 0.93 Ag 0.07 H x progressively decreased with increasing hydrogen content and vanished at [H]/[Pd 0.93 Ag 0.07 ] = 0.4. The disappearance of the susceptibility coincided with the termination of the plateau region of the isotherms. This fact can be explained by the rigid band model, according to which the vacant part of d-band of Pd 0.93 Ag 0.07 can accept electrons from absorbed hydrogen atoms.