99-Ru Moessauer study of the local environment of Rh and Ru in β Pdhsub(x)

The 89 keV Moessbauer resonance in 99-Ru was used to obtain information on the local hydrogen distribution near substitutional Rh and Ru atoms in β PdHsub(x). The emission spectra of sources of 99-Rh in PdHsub(x) represent the local environment of Rh. They are single lines of virtually the natural width throughout the β phase; in the mixed phase region, two separate single lines attributable to the α and β phase, respectively, occur. The Ru environment is represented by spectra taken with absorbers of 99-Ru in PdHsub(x). These exhibit complex Moessbauer patterns resulting mainly from a distribution of isomer shifts. The data indicate that the six hydrogen sites nearest to Rh solutes are all occupied throughout the β phase region, whereas in the vicinity of Ru solutes a distribution of hydrogen occupancies exists except at very high (x >= 0.9) hydrogen concentrations, for which all nearest neighbour sites become occupied. (orig.)