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  Czub, J.; Jamka, W.; Przewoznik, J.; Zarzecka, A.; Hoser, A.; Wallacher, D.; Grimm, N.; Gondek, Gondek: Structural peculiarities in the beta phase of the La_0.75Ce_0.25Ni_4.8Al_0.2 deuterides. Journal of Alloys and Compounds 788 (2019), p. 533-540

10.1016/j.jallcom.2019.02.259

Abstract:
In this contribution the structural, magnetic and sorption properties of the novel La0.75Ce0.25Ni4.8Al0.2 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 b phase. Unexpectedly, the b phase belongs to the same P6/mmm space group as the hydrogen poor a phase. Moreover, the b phase behaves like a solid solution on the plateau of the pressure-composition-temperature (PCT) curve. The deuterium sites and their occupations in both a and b 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.