Non-stoichiometric LaVO3. I. Synthesis and physical properties

Abstract

The effects of non-stoichiometry in lanthanum vanadium(III) oxide on unit-cell dimensions and thermal and magnetic properties are described. Samples with nominal composition La1-xVO3-y were synthesized form citrate solutions. The final reduction of Vv intermediates was achieved using zirconium getter or reductive gas mixtures. Two types of non-stoichiometry were proven. The La deficiency, La1-xVO3, is substantial. According to powder X-ray diffraction, the homogeneity width is 0.00 ≤x≤0.09±0.01 for samples annealed at 1273 K. Unit-cell data show that the range is clearly temperature dependent. In addition there are clear indications for La-excessive non-stoichiometry, LaV1-zO3-y. According to high-temperature powder X-ray diffraction, non-stoichiometric La1-xVO3 of the orthorhombic GdFeO3-type undergoes a phase transition to the rhombohedral LaAlO3-type around 770 K. Stoichiometric LaVO3 does not show such behaviour. The non-stoichiometry has a pronounced effect on the magneto-structural phase transition occurring for LaVO3 at 140 K. For La0.92VO3 magnetic susceptibility data indicate antiferromagnetic ordering below 70 K, whereas for La0.90VO3 paramagnetic behaviour was observed down to 5 K. Anomalous, negative magnetization was observed for field-cooled samples of La1-xVO3 (x≤0.08) with average formal oxidation number of vanadium higher than three. © Acta Chemica Scandinavica 1998.