Cooperative Jahn-Teller effect and electron-phonon coupling in La(1-x)A(x)MnO(3)

A classical model for the lattice distortions of La(1-x)A(x)MnO(3) is derived and, in a mean field approximation, solved. The model is based on previous work by Kanamori and involves localized Mn d electrons (which induce tetragonal distortions of the oxygen octahedra surrounding the Mn) and localized holes (which induce breathing distortions). Parameters are determined by fitting to the room temperature structure of LaMnO3. The energy gained by formation of a local lattice distortion is found to be large, most likely approximate to 0.6 eV per site, implying a strong electorn-phonon coupling and supporting polaronic models of transport in the doped materials. The structural transition is shown to be of the order-disorder type; the rapid x dependence of the transition temperature is argued to occur because added holes produce a ''random'' field which misaligns the nearby sites.