SURFACE SEGREGATION OF HYDROGEN ISOTOPES IN TRANSITION-METAL HYDRIDES

The surface segregation of hydrogen isotopes in ordered transition-metal hydrides is studied under the following assumptions: (i) each hydrogen isotope atom vibrates independently, (ii) the vibrations are harmonic (therefore, in particular, the frequencies of the various isotopes at equivalent positions are scaled by the square root of their mass ratio), and (iii) the frequencies of an isotope in the first undersurface layer are different from those in the bulk. Assumptions (i) and (ii) back on experimental evidence. The case of disordered unsaturated hydrides is also considered.