A comparative study of the electronic structures of SrCu2O2 and PbCu2O2 by density functional theory, high resolution X-ray photoemission and electron paramagnetic resonance spectroscopy

The electronic structures of SrCu2O2 and PbCu2O2 have been studied by density functional theory calculations in conjunction with high resolution X-ray photoemission spectroscopy (XPS) and electron paramagnetic resonance spectroscopy (EPR). In both materials there is linear O-Cu-O coordination and a band of Cu 3d states sits above a band of O 2p states, but with strong hybridisation between the two. The Pb ions in PbCu2O2 introduce new states of dominant Pb 6s atomic character below the bottom of the O 2p valence band together with states of mixed Pb 6s, O 2p and Cu 3d character at the top of the O 2p valence band. Hole states introduced by K doping in PbCu2O2 are shown to reside in anisotropic sites with clearly defined hyperfine couplings to Cu-63 as revealed by EPR. Broadening of the EPR signal in K-doped SrCu2O2 is associated with averaging of the g value and Cu hyperfine anisotropy due to facile hole hopping. It is concluded that replacement of Sr with Pb does not facilitate delocalisation of the holes.