The local and intermediate structure of stoichiometric ${\mathrm{LaMnO}}_3$ has been studied in the pseudocubic and rhombohedral phases at high temperatures (300–1150 K). Neutron powder diffraction data were collected and a combined Rietveld and high real space resolution atomic pair distribution function analysis was carried out. The nature of the Jahn-Teller (JT) transition around 750 K is confirmed to be orbital order to disorder. In the high-temperature orthorhombic ($O$) and rhombohedral ($R$) phases, the ${\mathrm{MnO}}_6$ octahedra are still fully distorted locally. More importantly, the intermediate structure suggests the presence of local ordered clusters of diameter $\sim 16\AA$ ($\sim 4$ ${\mathrm{MnO}}_6$ octahedra) implying strong nearest-neighbor JT antiferrodistortive coupling. These clusters persist well above the JT transition temperature even into the high-temperature $R$ phase.

• Received 12 August 2004

DOI:https://doi.org/10.1103/PhysRevLett.94.177203