The Jahn-Teller structural transition in stoichiometric LaMnO 3

Abstract

The parent compound of the giant magnetoresistance perovskite Mn-oxides, LaMnO 3, has an orthorhombic Pbnm crystal structure at room temperature characterized by the presence of an anti-ferrodistorsive e g(1):e g(2) orbital ordering due to a cooperative Jahn-Teller effect. The compound undergoes a structural phase transition at T JT ≈ 790 K, above which the orbital ordering disappears. There is no change in symmetry, although the lattice becomes metrically cubic on the high-temperature side. The refinement of the crystal structure shows that MnO 6 octahedra become much more regular above T JT and the thermal parameter of oxygen atoms increases significantly. The observed average cubic lattice is probably the result of dynamical spatial fluctuations of the underlying small orthorhombic distortion.