We have studied the electronic structure of ${\mathrm{Y}}_{1-x}{\mathrm{Ca}}_x{\mathrm{VO}}_3$ by x-ray-absorption and resonant photoemission spectroscopy. Upon hole doping the parent Mott-Hubbard insulator ${\mathrm{YVO}}_3,$ an insulator-metal transition occurs at around $x\approx \mathrm{0.5.}$ Resonant V $3p$ photoemission spectroscopy shows that the states near to the Fermi level are of predominantly V $3d$ character; in ${\mathrm{CaVO}}_3,$ a Fermi edge is present. In the oxygen $1s$ x-ray-absorption spectra, the hole doping is reflected in a large increase of the spectral weight near threshold. Because large changes also appear in the vanadium $2p$ absorption edge, we conclude that the doped holes are of mixed O and V character. The results also indicate that the amount of O character increases with doping. The development of the photoemission and x-ray-absorption spectral weight differs from the rigid-band-like behavior predicted by one-electron band theory or Hubbard-model calculations. Our O $1s$ x-ray-absorption spectra show good correspondence with the optical spectra, indicating that interband features in the optical spectra are attributed to O $2p$ to V $3d$ charge-transfer excitations.

• Received 29 May 1998

DOI:https://doi.org/10.1103/PhysRevB.59.7422