Phase separation in thermoelectric delafossite CuFe(1-x)Ni(x)O(2) observed by soft x-ray magnetic circular dichroism

Abstract

Electronic structures of Ni-doped CuFe1-xNixO2 delafossite oxides (0 <= x <= 0.03) have been investigated by employing soft x-ray magnetic circular dichroism (XMCD). Finite XMCD signals are observed for Fe, Ni, and Cu 2p states, and valence states of Cu, Fe, and Ni ions are nearly monovalent (Cu+), trivalent (Fe3+), and divalent (Ni2+), respectively, for all x <= 0.03. Tiny magnetic impurities could be detected by employing XMCD. Fe and Ni 2p XMCD signals are identified due to ferrimagnetic spinel impurities of CuFe2O4 and NiFe2O4. XMCD signals for Cu 2p states arise from divalent Cu2+ ions. Thermoelectrical properties are found to be very sensitive to the very little impurity phase present in delafossite oxides. (C) 2011 American Institute of Physics. [doi:10.1063/1.3609248]