Transition from the layered Sr2RhO4 to the monodimensional Sr4RhO6 phase

Study of the structural changes occurring during the reduction process of t he Sr2RhO4+delta (214), n=1 term of the Ruddlesden and Popper series, shows that fur delta < 0.02 values, this material dissociates into the Sr4RhO6 ( 316) monodimensional phase, <alpha>=infinity, beta =0 compound of the (A(3) B(2)O(6))(alpha)- (A(3)B(3)O(9))(rho) family, and Rh metal. During the firs t stage, this process occurs by the formation of an intergrowth between the (214) and (416) materials which can be only detected by high resolution el ectron microscopy and is easily interpreted on the basis of the structural relationship established between them. Further reduction allows the segrega tion of both phases as separated entities, which coexist with Ph metal. The dis sociation process is reversible and, under oxidizing conditions, a lay ered material with anionic composition delta = 0.06 is always obtained. Thi s behaviour seems to be a general way of accommodating the compositional ch anges in layered A(2)BO(4) phases where the B cation is always in a octahed ral environment. The structural mechanism of this transformation is propose d, and the structural relationship between these two low-dimensional oxides is established.