Evidence for charge localization in the ferromagnetic phase of La1ÀxCaxMnO3 from high real-space-resolution x-ray diffraction

High real-space-resolution atomic pair distribution functions of La12xCaxMnO3 (x50.12, 0.25, and 0.33! have been measured using high-energy x-ray powder diffraction to study the size and shape of the MnO6 octahedron as a function of temperature and doping. In the paramagnetic insulating phase we find evidence for three distinct bond lengths which we ascribe to Mn-O, Mn-O-short, and Mn-O-long bonds, respectively. In the ferromagnetic metallic ~FM! phase, for x50.33 and T520 K, we find a single Mn-O bond length; however, as the metal-insulator transition is approached either by increasing T or decreasing x, intensity progressively appears around r52.15 and in the region 1.8521.9 Å suggesting the appearance of Mn-O-long bonds and short Mn-O bonds. This is strong evidence that charge localized and delocalized phases coexist close to the metal-insulator transition in the FM phase.