High real-space-resolution atomic pair distribution functions of ${\mathrm{La}}_{1-x}{\mathrm{Ca}}_x{\mathrm{MnO}}_3$ $(x=0.12,$ 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 ${\mathrm{Mn}}^{4+}-\mathrm{O},$ ${\mathrm{Mn}}^{3+}-\mathrm{O}$-short, and ${\mathrm{Mn}}^{3+}-\mathrm{O}$-long bonds, respectively. In the ferromagnetic metallic (FM) phase, for $x=0.33\mathrm{}$ and $T=20\mathrm{}\hspace{0.5em}\mathrm{K},$ 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 $r=2.15\mathrm{}$ and in the region $1.85-1.9\hspace{0.5em}\AA$ suggesting the appearance of ${\mathrm{Mn}}^{3+}-\mathrm{O}$-long bonds and short ${\mathrm{Mn}}^{4+}-\mathrm{O}$ bonds. This is strong evidence that charge localized and delocalized phases coexist close to the metal-insulator transition in the FM phase.

• Received 21 July 1999

DOI:https://doi.org/10.1103/PhysRevB.62.1203