Hydrogen-induced phase separation in amorphousCu0.5Ti0.5alloys. III. Computer-simulation studies

Neutron-diffraction results on amorphous CuTi hydrides have been used to construct a model for the structure of the amorphous matrix and the location of hydrogen. The important modification of the metallic matrix upon hydrogen absorption is simulated by a Monte Carlo procedure with nearest-neighbor exchanges on an $A_{50}$ $B_{50}$ alloy with no size effect. Both initial (chemically ordered) and final (phase-separated) configurations are then numerically relaxed with a set of three Morse potentials in order to account for the size difference between Cu and Ti atoms. The influence of order and size difference on the distribution of interstitial sites is also studied. A good agreement with the experimental interference functions and reduced atomic distribution functions is obtained both before and after hydrogen loading. On the basis of the experimental results, hydrogen is then introduced in the metallic matrix by considering the occupancy of ${\mathrm{Ti}}_4$ sites only and with hydrogen-hydrogen nearest-neighbor exclusion. Both the variation of the maximum hydrogen content with alloy composition and the partial metal-hydrogen and hydrogen-hydrogen atomic distribution functions are found to agree with experiment.