Passage from T-type to T'-type arrangement by reducing R4Ni3O10 to R4Ni3O8 (R = La, Pr, Nd)

For the first time a triple-layer T'-type arrangement has been stabilized in mixed-valence Ni1+/Ni2+ nickelates R4Ni3O8 (R = La, Pr, Nd). These compounds are obtained by reducing mixed-valence Ni2+/Ni3+ oxides R4Ni3O10, the n = 3 members of the Ruddlesden-Popper-type series Rn+1NinO3n+1. In the same way that R4Ni3O10 adopts the triple-layer structure intermediate between single-layer T-type and perovskite structures, R4Ni3O8 can be considered as the triple-layer intermediate between the T' and so-called infinite-layer structural types. The compounds R4Ni3O8 (R = La, Pr, Nd) are black semiconductors and they are stable in air at room temperature. The passage from R4Ni3O10 to R4Ni3O8 is reversible by reduction/oxidation under hydrogen/oxygen at moderate temperature. It is expected that a similar reduction process can occur in triple-layer La4Cu3O10