Novel ABO_3 oxides related to perovskite and YAlO_3 structure types in the La-B-V-O (B=Ni,Cu) systems

摘要

The synthesis,structure and magnetic properties of mixed-metal oxides of ABO_3 composition in the La-B-V-O (B=Ni,Cu) systems are described in the present paper.While the B=Ni oxides adopt GdFeO_2-like perovskite structure containing disorbered nickel and vanadium at the octahedral B site,La_3Cu_2VO_9 crystallizes in a YAlO_3-type structure.A detailed investigation of the superstructure of nominal La_3Cu_2VO_9 by WDS analysis and Rietveld refinement of powder XRD data reveal that the likely composition of the phase is La_3Cu_2VO_9 by WDS analysis and Rietveld refinement of powder XRD data reveal that the likely composition of the phase is La_(13)Cu_9V_4O_(38.5),where the Cu and V atoms are ordered in a 13a_h~(1/2) (a_h=hexagonal a parameter of YAlO_3-like subcell) superstructure.Magnetic susceptibility data support the proposed superstructure consisting of triangular Cu_3 clusters.At low temperatures,the magnetic moment corresponds to S=1/2 per Cu_3 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 YAlO_3 structure is formed around La_3Cu_2VO_9 composition in the copper system,a continuous series of perovskite-GdFeO_3 solid solutions,LaLi_(1-x)V_xO_3 for O<=x<=1/3 seems to be obtained in the nickel systme,where the oxidation state of nickel varies from 3+ to 2+.