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 spectros copy (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 compound s, 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 electr onic state of La0.9CoO3-delta is quite different from that of Sr-subst ituting La0.8Sr0.2CoO3-delta. In order to explain the difference betwe en La-deficiency and Sr-substitution effects in valence controlling of LaCoO3, it is considered that Sr substitution produces the Co 3d hole s and La deficiency yields the O 2p holes.