Novel ABO₃ oxides related to perovskite and AlO₃ structure types in the La-B-V-O (B = Ni, eu) systems

Abstract

The synthesis, structure and magnetic properties of mixed-metal oxides of ABO₃ composition in the La-B-V-O (B =Ni,Cu) systems are described in the present paper. While the B = Ni oxides adopt GdFeO₃-like perovskite structure containing disordered nickel and vanadium at the octahedral B site, La₃Cu₂VO₉ crystallizes in a YAlO₃-type structure. A detailed investigation of the superstructure of nominal La₃Cu₂VO₉ by WDS analysis and Rietveld refinement of powder XRD data reveal that the likely composition of the phase is La₁₃

Cu₉V₄O_38,5, where the Cu and V atoms are ordered in a √13<i>a</i>_h<i> </i>(<i>a</i>_h<i> </i>= hexagonal <i>a </i>parameter of YAlO₃-like subcell) superstructure. Magnetic susceptibility data support the proposed superstructure consisting of triangular Cu₃ clusters. At low temperatures, the magnetic moment corresponds to S = 1/2 per Cu₃ cluster, while at high temperatures the behavior is Curie-Weiss like, showing S = 1/2 per copper. The present work reveals the contrasting behavior of La-Cu-V-O and La-Ni-V-O systems: while a unique line-phase related to YAlO₃ structure is formed around La₃Cu₂VO₉ composition in the copper system, a continuous series of perovskite-GdFeO₃, solid solutions, LaNi_1-x V_xO₃ for 0 ≤ x ≤ 1/3 seems to be obtained in the nickel system, where the oxidation state of nickel varies from 3+ to 2+.