La-site shift as probe for Jahn-Teller effect

We observe two consecutive transitions in La1-xCaxMnO3, x=0.19: ferromagnetic ordering at Tc = 177 K and Jahn-Teller orbital ordering at T_JT = 150 K. The presence of a ferromagnetic insulating state below T_JT shows that the metallic phase is bound by ferromagnetic and Jahn- Teller ordering, and not induced by a critical doping concentration. The A-site shift is found to be a good indicator of Jahn-Teller ordering. Furthermore, the A-site shift does not disapppear above T_JT, indicating a dynamical behaviour of the distorted MnO6 octahedra.