Crystal symmetry of La3Cu2VO9 and La4Cu3MoO12 derived from the YAlO3 hexagonal structure by transmission electron microscopy

La4Cu3MoO12 and La3Cu2VO9, homeotypes of YAlO3, an ABO(3) hexagonal phase, have been investigated using a variety of transmission electron microscopy techniques. Both compounds possess the same hexagonal subcell but exhibit d ifferent supercells. The unit cell parameters and symmetry have been determ ined using selected area and convergent beam electron diffraction technique s. For La3Cu2VO9, electron energy loss spectroscopy and energy dispersive X -ray spectroscopy were used to determine the oxidation-state of vanadium an d the cation stoichiometry, respectively, which conforms to La3Cu2VO9. This paper highlights the need for multitechnique approaches to complex oxide s tructures. (C) 2001 Editions scientifiques et medicales Elsevier SAS. All r ights reserved.