Ba 2Co 9O 14 is a charge-ordered Co2 +/3 + cobaltite that consists of building blocks of CdI 2-type Co2 +/3 +O 6/3 layers, face-shared Co3 + 3O 12 octahedral trimers, and corner-sharing Co2 +O 4 tetrahedra. The Co-L 2,3 x-ray absorption spectroscopy spectrum at room temperature indicates a high and a low spin state for Co2 + and Co3 + ions, respectively. Measurements of high-temperature resistivity and thermoelectric power revealed an insulator-to-insulator phase transition at T t = 570 K, above which the inverse magnetic susceptibility χ -1(T) deviates from the Curie-Weiss law. By using a combination of soft x-ray absorption spectroscopy at the O-K edge and high-resolution synchrotron x-ray powder diffraction measurements on crossing T t, we have successfully determined the origin of this phase transition as a low-to-higher spin-state transition of Co3 + ions within the face-shared Co 3O 12 octahedral trimers in Ba 2Co 9O 14.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - 23 Mar 2012|