Structural Aspects of the Crystallographic-Magnetic Transition in LaVO 3 around 140 K

Abstract

The perovskite-like compound LaVO 3 undergoes a crystallographic-antiferromagnetic transition at about 140 K. The structure of LaVO 3 has been determined at room temperature and just above (150 K) and below (100 K) the transition. Synchrotron X-ray and neutron powder diffraction techniques were used. The lattice parameter variation vs temperature and the structural refinements revealed that above the transition the structure of LaVO 3 is of GdFeO 3 type; namely, it is orthorhombic with lattice parameters at room temperature a = 5.55548, b = 7.84868, and c = 5.55349 Å and space group Pnma. The orthorhombic distortion of the structure is very similar to that of isostructural LaFeO 3. At 100 K, below the transformation temperature, the structure is monoclinic with lattice parameters: a = 5.59360, b = 7.75951, c = 5.56490 Å γ = 90.125° and space group P2 1/ a. In the orthorhombic structure all V sites are equivalent, but two independent sites, V1 and V2, are observed in the monoclinic structure. These two sites form alternate layers along the b axis. Above the transition all the V octahedra are tilted around the three crystallographic axes and are elongated along the [110] direction. The elongation increases at the transition and occurs in different directions, 90° apart, in the V1 and V2 octahedra.