Probing the local structure of doped manganites using the atomic pair distribution function

We have used atomic pair distribution function (PDF) analysis based on neutron powder diffraction data to investigate the local structure of the colossal magnetoresistant manganite La_0.75Ca_0.25MnO₃ as a function of temperature. In the doping range 0.27 < x < 0.5 these materials show a metal-to-insulator transition, transforming from a ferromagnetic metal (FM) at low temperature to a paramagnetic insulator (PI). We can probe the charge distribution of the sample using the PDF by searching for evidence of Jahn-Teller (JT) distorted octahedra, implying the presence of Mn³⁺ ions. A two-phase model based on the local structures of the FM and PI phases was used to refine the experimental PDFs quantitatively. We observe the co-existence of both phases over a wide temperature range: approximately 10% of the localized JT phase (PI) is present event at the lowest temperature (T = 20 K), whereas at room temperature nearly half of the sample remains in the delocalized (FM) phase.