Hysteresis and thermodynamic characterization of Nb1−x Crx (x=0.03, 0.05, 0.1)

Pressure-composition isotherms for hydrogen absorption and desorption are determined for Nb1−xCrx (x=0.03, 0.05, 0.1) over the temperature range 320 to 370 K. Pronounced hysteresis are observed at all temperatures. The average enthalpies ([H]/[M]=0.2–0.8) for hydride formation are −14.0, −14.7 and −15.9 kJ/mol H and for hydride decomposition are 23.4, 23.6 and 22.7 kJ/mol H for x values of 0.1, 0.05 and 0.03. The hysteresis effect is explained in terms of an elastic strain energy effect.