Valence State of the Chromium Ion and Electrical Conductivity of Ca-Doped Lanthanum Chromite

✍ Scribed by G. J. Zhang; Y. Q. Jia

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 162 KB
• Volume: 215
• Category: Article
• ISSN: 0370-1972
• DOI: 10.1002/(sici)1521-3951(199910)215:2<1057::aid-pssb1057>3.0.co;2-m

✦ Synopsis

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 Cr 4 ions in La 1Àx Ca x CrO 3 will become larger with increasing x and the electrical conductivity is in proportion with the relative content of Cr 4 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 t 2g and e g subbands from the Cr atom and a narrowing of the gap between the t 2g 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 Cr 4 ions and to an increasing number of holes in the band. A linear relationship between the elecrtrical conductivity and the relative Cr 4 ion content may be valid only for lanthanum chromite with a small amount of Ca.

* ) The relative content of Cr 4 ions is interpolated from the results obtained by the tight-binding approximation for neighboring compounds.