NONSTOICHIOMETRIC LAVO3 - I - SYNTHESIS AND PHYSICAL-PROPERTIES

The effects of non-stoichiometry in lanthanum vanadium(III) oxide on u nit-cell dimensions and thermal and magnetic properties are described. Samples with nominal composition La1-xVO3-y were synthesized form cit rate solutions. The final reduction of VV intermediates was achieved u sing zirconium getter or reductive gas mixtures. Two types of non-stoi chiometry were proven. The La deficiency, La1-xVO3, is substantial. Ac cording to powder X-ray diffraction, the homogeneity width is 0.00 les s than or equal to x less than or equal to 0.09 +/- 0.01 for samples a nnealed at 1273 K. Unit-cell data show that the range is clearly tempe rature dependent. In addition there are clear indications for La-exces sive non-stoichiometry, LaV1-zO3-y. According to high-temperature powd er X-ray diffraction, non-stoichiometric La1-xVO3 of the orthorhombic GdFeO3-type undergoes a phase transition to the rhombohedral LaAlO3-ty pe around 770 K. Stoichiometric LaVO3 does not show such behaviour. Th e non-stoichiometry has a pronounced effect on the magneto-structural phase transition occurring for LaVO3 at 140K. For La0.92VO3 magnetic s usceptibility data indicate antiferromagnetic ordering below 70 K, whe reas for La0.90VO3 paramagnetic behaviour was observed down to 5 K. An omalous, negative magnetization was observed for field-cooled samples of La1-xVO3 (x less than or equal to 0.08) with average formal oxidati on number of vanadium higher than three.