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 LaCoO3 has been investigated by using x-ray photoelectron spectroscopy (XPS). On the basis of the relationship between the intensity of the T-2(2) line and the amount of low-spin Co3+ ions in these compounds, it is pointed out that La0.9CoO3-delta is in a highly covalent low-spin state and La0.8Sr0.2CoO3-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 La0.9CoO3-delta is quite different from that of Sr-substituting La0.8Sr0.2CoO3-delta. In order to explain the difference between La-deficiency and Sr-substitution effects in valence controlling of LaCoO3, it is considered that Sr substitution produces the Co 3d holes and La deficiency yields the O 2p holes.