No abstract

The valence state of the Cr ion in Ca‐doped lanthanum chromite compounds without or with oxygen deficiency has been calculated by means of a tight‐binding approximation on the basis of the EHMO approximation. The results indicate that the relative content of Cr4+ ions in La1—xCaxCrO3 will become larger with increasing x and the electrical conductivity is in proportion with the relative content of Cr4+ ions in the compound. The difference between some reported experimental results in the same compounds is mainly due to the different oxygen deficiency in the samples. Doping can lead not only to a splitting of the t2g and eg subbands from the Cr atom and a narrowing of the gap between the t2g subband from the Cr atom and 2p band from the O atom, but also leads to an increase of the relative content of the acceptor of Cr4+ ions and to an increasing number of holes in the band. A linear relationship between the elecrtrical conductivity and the relative Cr4+ ion content may be valid only for lanthanum chromite with a small amount of Ca.