Direct observation of lattice polaron formation in the local structure of La1-xCaxMnO3

The local atomic structure of La1-xCaxMnO3 (x = 0.12, 0.21, and 0.25) has been studied using pair-distribution-function analysis of neutron powder-diffraction data. A change is seen in the local structure which can be correlated with the metal-insulator transition in the x = 0.21 and 0.25 samples. This local structural change is modeled as an isotropic collapse of oxygen towards Mn of magnitude delta = 0.12 Angstrom occurring on one in four Mn sites. We argue that this is the direct observation of lattice polaron formation, associated with the metal-insulator transition in these materials.