A TRANSITION FROM LARGE TO SMALL POLARONS IN THE La0.75Ca0.25MnO3 PEROVSKITE SYSTEM

A quantitative determination of the statistical distribution of the Mn-O instantaneous bond lengths in the La0.75Ca0.25MnO3 system by Mn K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy shows that the giant magneto-resistance (GMR) transition occurs at a crossover from ametallic phase with large (or intermediate) polarons to an insulating phase where small polarons coexist with large (or intermediate) polarons. In the GMR region, the twoMn polaronic domains coexist and share half of the space.