Electronic states of PrCoO3:: x-ray photoemission spectroscopy and LDA+U density of states studies

Electronic states of PrCoO3 are studied using x-ray photoemission spectroscopy. The Pr 3d(5/2) core level and valence band (VB) were recorded using an Mg K alpha source. The core level spectrum shows that the 3d5/2 level is split into two components of multiplicity four and two, respectively, due to coupling of the spin states of the hole in 3d5/2 with the Pr 4f hole spin state. The observed splitting is 4.5 eV. The VB spectrum is interpreted using density of states (DOS) calculations under LDA and LDA + U. It is noted that LDA is not sufficient to explain the observed VB spectrum. Inclusion of onsite Coulomb correlation for Co 3d electrons in LDA + U calculations gives DOS which is useful in qualitative explanation of the ground state. However, it is necessary to include interactions between Pr 4f electrons to get better agreement with the experimental VB spectrum. It is seen that the VB consists of Pr 4f, Co 3d and O 2p states. Pr 4f, Co 3d and O 2p bands are highly mixed, indicating strong hybridization of these three states. The band near the Fermi level has about equal contributions from Pr 4f and O 2p states with somewhat smaller contribution from Co 3d states. Thus in the Zaanen, Sawatzky and Allen scheme PrCoO3 can be considered as a charge transfer insulator. The charge transfer energy A can be obtained using LDA DOS calculations and the Coulomb-exchange energy U' from LDA + U. The explicit values for PrCoO3 are Delta = 3.9 eV and U' = 5.5 eV; the crystal field splitting and 3d bandwidth of Co ions are also found to be 2.8 and 1.8 eV, respectively.