SPLIT PLATEAUS IN THE LANI5-H SYSTEM AND THE EFFECT OF SN SUBSTITUTION ON SPLITTING

Split plateaux corresponding to the appearance of an additional, gamma , phase, which have been observed elsewhere, have been found in this r esearch for closely stoichiometric LaNi5. The plateaux were found to b e very horizontal at lower temperatures before splitting occurs. Some splitting in the decomposition plateau was found even at 273 K after c ycling at more elevated temperatures. A virgin sample showed a small a mount of splitting of the decomposition plateau at 373 K and this spli tting increased markedly for the second cycle and its extent became ne arly constant after about 5 or 6 cycles at 373 K. Van't Hoff plots wer e made using data from the split plateaux. Split plateaux were not fou nd for any of the LaNi5-xSnx alloys which were examined at 373 K, i.e. , those with x greater than or equal to 0.05, after cycling where LaNi 5, exhibited split plateaux for the first cycle.