An X-ray diffraction study was performed by using a cubic anvil press and a synchrotron radiation source. The samples were 1mm in diameter, 0.15mm thick, and were cut from a rolled sheet of Pd0.8Rh0.2 alloy which had been prepared from 3N8-purity Pd and 3N-purity Rh by arc-melting in Ar, homogenizing (850C, 48h, vacuum), rolling and annealing (850C, 2h, vacuum). Powdered samples (200 mesh), mixed with 10vol%BN, were also used. The results permitted an estimate (10-17m2/s) to be made of the diffusivity of metal atoms during phase separation. An upper bound (10-24m2/s) on the diffusivity in vacuum was based upon the absence of observable phase separation after nearly 9000h at 600C. The diffusivity was therefore enhanced, by a factor of at least 107, by 5GPa of H. It was suggested that this H-induced diffusion of metal atoms was due to an increased number of metal atom vacancies. The observed diffusion enhancement could be explained if the concentration of vacancies was increased by more than 107. The vacancy concentration that was required in the hydride phase was estimated to be greater than 0.01.

K.Watanabe, N.Okuma, Y.Fukai, Y.Sakamoto, Y.Hayashi: Scripta Materialia, 1996, 34[4], 551-7