Investigation of X-ray photoelectron spectroscopy and electrical conductivity properties of the layered perovskite LnBaCo2O5+d (Ln = Pr, Nd, Sm, and Gd) for IT-SOFC

Chemical states of the layered perovksite LnBaCo(2)O(5+d) (Ln = Pr, Nd, Sm, and Gd) are investigated using the x-ray Photoelectron Spectroscopy method. For the Co spectra of the LnBaCo(2)O(5+d) oxide systems, the two main peaks located at binding energies (BEs) of 779.65 eV and 794.96 eV are assigned to Co 2p (3/2) and Co 2p (1/2) of PrBaCo2O5+d (PBCO) and are ascribed to 779.86 eV and 795.08 eV of NdBaCo2O5+d (NBCO). In addition, the lower binding energy (LBE) and higher binding energy (HBE) of SmBaCo2O5+d (SBCO) were found to be 779.67 eV and 795.02 eV, respectively; the LBE and HBE of GdBaCo2O5+d (GBCO) were 779.73 eV and 795.03 eV, respectively. The BEs of the mixture state of Co3+ and Co4+ ions in PBCO, NBCO, SBCO, and GBCO were approximately located in the vicinity of 803.24 eV to 804.47 eV. As for the electrical conductivities of the layered perovskites, PBCO and NBCO had metallic characteristics over the whole temperature range tested while SBCO and GBCO exhibited metal-insulator transition (MIT) behavior.