Orbital correlations in the pseudo-cubic \emph{O} and rhombohedral $R$-phases of LaMnO${}_3$

Abstract

The local and intermediate structure of stoichiometric LaMnO${}_3$ has been studied in the pseudocubic and rhombohedral phases at high temperatures (300 to 1150 K). Neutron powder diffraction data were collected and a combined Rietveld and high real space resolution atomic pair distribution function analysis 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 MnO${}_6$ octahedra are still fully distorted locally. The data suggest the presence of local orbitally ordered clusters of diameter $\sim 16$ Å($\sim$four MnO${}_6$ octahedra) implying strong nearest neighbor JT anti-ferrodistortive coupling.

4 pages, 4 figures, submitted to Phys. Rev. Let