Passage from T-type to T′-type arrangement by reducing R4Ni 3O 10 to R4Ni 3O 8 ( R = La, Pr, Nd)

Abstract

For the first time a triple-layer T′-type arrangement has been stabilized in mixed-valence Ni 1+ Ni 2+ nickelates R 4Ni 3O 8 ( R = La, Pr, Nd). These compounds are obtained by reducing mixed-valence Ni 2+ Ni 3+ oxides R 4Ni 3O 10, the n = 3 members of the Ruddlesden-Popper-type series R n+1 Ni n O 3 n+1 . In the same way that R 4Ni 3O 10 adopts the triple-layer structure intermediate between single-layer T-type and perovskite structures, R 4Ni 3O 8 can be considered as the triple-layer intermediate between the T′ and so-called infinite-layer structural types. The compounds R 4Ni 3O 8 ( R = La, Pr, Nd) are black semiconductors and they are stable in air at room temperature. The passage from R 4Ni 3O 10 to R 4Ni 3O 8 is reversible by reduction/oxidation under hydrogen/oxygen at moderate temperature. It is expected that a similar reduction process can occur in triple-layer La 4Cu 3O 10.