Structural peculiarities in the β phase of the La0.75Ce0.25Ni4.8Al0.2 deuterides
Abstract In this contribution the structural, magnetic and sorption properties of the novel La 0.75 Ce 0.25 Ni 4.8 Al 0.2 alloy and its deuterides are discussed. The collected data indicate good stability of the alloy during the cycle-life and thermal treatment tests. Particularly, the desorption pressure is almost constant versus the cycle number. The results of the in-situ neutron diffraction studies show the unusual behaviour of the deuterium rich β phase. Unexpectedly, the β phase belongs to the same P 6/ mmm space group as the hydrogen poor α phase. Moreover, the β phase behaves like a solid solution on the plateau of the pressure-composition-temperature (PCT) curve. The deuterium sites and their occupations in both α and β phases are determined from the neutron diffraction data, giving the first-hand insight into the mechanism of the PCT hysteresis. As far as the magnetic properties are concerned, cerium is trivalent in the investigated alloy. However, no magnetic ordering down to 3 K is observed. It can be concluded that the sorption properties of the crystal depend on the cerium valence, what distinguishes the alloy from the other compositions.