Neutron Scattering Study of CoO6 Distortion and Its Relation to the Spin-State Transition in Pr0.5Ca0.5CoO3

This study compares the electrical resistivity, magnetization, and high-resolution neutron powder diffraction data obtained for Pr0.5Ca0.5CoO3 and Pr0.5Ca0.5CoO3-delta (delta similar to 0.045). Although both samples exhibit similar structural parameters, the distortion of the CoO6 octahedra is weaker in Pr0.5Ca0.5CoO3-delta than in Pr0.5Ca0.5CoO3 at low temperatures. This reduced distortion decreases the electron-lattice coupling, which increases the itinerant nature of the e. electrons in the oxygen-deficient sample. In addition, the oxygen deficiency can add Co3+ ions into Pr0.5Ca0.5CoO3-delta, yielding an increased population of e(g) electrons. As a result, the sharp spin-state transition observed in Pr0.5Ca0.5CoO3 is suppressed in Pr0.5Ca0.5CoO3-delta, which exhibits a lower magnitude of resistivity and stronger magnetism at low temperatures.