Abstract
The parent compound of the giant magnetoresistance Mn-perovskite, , has been studied by thermal analysis and high-resolution neutron-powder diffraction. The orthorhombic structure at room temperature is characterized by an antiferrodistorsive orbital ordering due to the Jahn-Teller effect. This ordering is evidenced by the spatial distribution of the observed Mn-O bond lengths. undergoes a structural phase transition at 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 octahedra become nearly regular above and the thermal parameter of oxygen atoms increases significantly. The observed average cubic lattice is probably the result of dynamic spatial fluctuations of the underlying orthorhombic distortion.
- Received 2 September 1997
DOI:https://doi.org/10.1103/PhysRevB.57.R3189
©1998 American Physical Society