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. © 1992.