Transition from itinerant to polaronic conduction in La1-xSrxCoO3 perovskites

Neutron diffraction and small-angle scattering on La1-xSrxCoO3 (0 < x less than or equal to 0.30) show that for x = 0.3 the system is near a two-phase percolation threshold and undergoes a transition from itinerant to polaronic conduction at the Curie temperature T-C. The stabilization of superparamagnetic clusters on warming through T-C is revealed by an anomalous thermal expansion of the volume and a deviation of the paramagnetic susceptibility from the Curie-Weiss law. The development of a temperature-dependent small-angle-scattering signal confirms that regions of short-range ferromagnetic order are present above T-C.