Electronic state and valence control of LaCoO3: Difference between La-deficient and Sr-substituting effects

The difference between La-deficient and Sr-substituting effects for La in LaCoO${}_{3}$ has been investigated by using x-ray photoelectron spectroscopy (XPS). On the basis of the relationship between the intensity of the ${}^{2}{T}_{2}$ line and the amount of low-spin Co${}^{3+}$ ions in these compounds, it is pointed out that La${}_{0.9}$CoO${}_{3\ensuremath{-}\ensuremath{\delta}}$ is in a highly covalent low-spin state and La${}_{0.8}$Sr${}_{0.2}$CoO${}_{3\ensuremath{-}\ensuremath{\delta}}$ is in a mixed spin state. From the Co $2p$ and valence-band XPS results, it is pointed out that the electronic state of La${}_{0.9}$CoO${}_{3\ensuremath{-}\ensuremath{\delta}}$ is quite different from that of Sr-substituting La${}_{0.8}$Sr${}_{0.2}$CoO${}_{3\ensuremath{-}\ensuremath{\delta}}.$ In order to explain the difference between La-deficiency and Sr-substitution effects in valence controlling of LaCoO${}_{3}$, it is considered that Sr substitution produces the Co $3d$ holes and La deficiency yields the O $2p$ holes.