Lattice effects in La12xCaxMnO3 „x50 ̃1...: Relationships between distortions, charge distribution, and magnetism

X-ray-absorption fine-structure measurements from the Mn and La K edges of samples of La12xCaxMnO3 (x50→1) are presented as a function of temperature. In the insulating state, distortions of the Mn-O environment are found to be linear with calcium concentration x . These distortions are consistent with a model where individual Mn sites have strong Jahn-Teller ~JT! distortions while Mn sites do not, although intermediate distortions are also possible. Comparisons to simulations of various possible bond length distributions show that these distortions are best modeled as a JT distortion, as opposed to charge disproportionation or other models. In the metallic state, at least ;70% of the distortion is removed. A similar effect is seen in the Mn-Mn bond length distribution. The La-O bond length distribution does not change significantly through the ferromagnetic transition, constraining possible changes in the Mn-O-Mn bond angle to less than 0.5°. The changes in the MnO6 distortion that occur near Tc are also present ~to a lesser degree! in an insulating sample with x50.12. The functional relation between the MnO6 distortions and the magnetization is determined, and compared to transport measurements. @S0163-1829~98!04917-0#