HYDROGEN UPTAKE OF PALLADIUM-GOLD ALLOYS STUDIED BY AU-197 MOSSBAUER-SPECTROSCOPY

Hydrides of Pd0.99Au0.01 and Pd0.90Au0.10 alloys were prepared electro lytically or under pressures of hydrogen gas up to 7.2 GPa and studied by Mossbauer spectroscopy with the 77 keV gamma-rays of Au-197. The o bserved isomer shifts show that in Pd0.99Au0.01Hx the interstitial sit es next to the gold atoms become occupied by hydrogen only at x greate r than or similar to 0.95. The isomer shifts observed at x less than o r similar to 0.95 are attributed to volume expansion and long range el ectronic effects. This interpretation is supported by the volume depen dence of the Au-197 isomer shift in Pd0.99Au0.01Hx measured at pressur es up to 6 GPa. In Pd0.90Au0.10Hx, hydrogenation at temperatures aroun d 325-degrees-C was found to cause the formation of goldrich zones.