Evidence for charge localization in the ferromagnetic phase of La{sub 1-x}Ca{sub x}MnO{sub 3} from high real-space-resolution x-ray diffraction

High real-space-resolution atomic pair distribution functions of ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}$ $(x=0.12,$ 0.25, and 0.33) have been measured using high-energy x-ray powder diffraction to study the size and shape of the ${\mathrm{MnO}}_{6}$ 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 ${\mathrm{Mn}}^{4+}\ensuremath{-}\mathrm{O},$ ${\mathrm{Mn}}^{3+}\ensuremath{-}\mathrm{O}$-short, and ${\mathrm{Mn}}^{3+}\ensuremath{-}\mathrm{O}$-long bonds, respectively. In the ferromagnetic metallic (FM) phase, for $x=0.33$ and $T=20 \mathrm{K},$ 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 $r=2.15$ and in the region $1.85\ensuremath{-}1.9 \AA{}$ suggesting the appearance of ${\mathrm{Mn}}^{3+}\ensuremath{-}\mathrm{O}$-long bonds and short ${\mathrm{Mn}}^{4+}\ensuremath{-}\mathrm{O}$ bonds. This is strong evidence that charge localized and delocalized phases coexist close to the metal-insulator transition in the FM phase.