Measurement of the local Jahn-Teller distortion in LaMnO_3.006

The atomic pair distribution function (PDF) of stoichiometric LaMnO₃has been measured. This has been fit with a structural model to extract the local Jahn-Teller distortion for an ideal Mn³⁺O₆octahedron. These results are compared to Rietveld refinements of the same data which give the average structure. Since the local structure is being measured in the PDF there is no assumption of long-range orbital order and the real, local, Jahn-Teller distortion is measured directly. We find good agreement both with published crystallographic results and our own Rietveld refinements suggesting that in an accurately stoichiometric material there is long-range orbital order as expected. The local Jahn-Teller distortion has two short, two medium, and two long bonds. This implies that there is some mixing of the d_3z²-r²and d_x²-y²states and the occupied state is not pure d_3z²-r²symmetry. The Debye temperature of the Mn and O ions has also been calculated as Θ_D(Mn)=1000 ± 100K, Θ_D(O_apical)=980 ± 30K, and Θ_D(O_basal)=601 ± 8K.