Titanates and Related Phases

The simplest conceptual way in which an insulating perovskite such as the archetypal alkaline earth titanates CaTiOj, SrTiOj and BaTiOj can be turned into a conductor is to introduce electrons into the empty 3d tj band formed from the orbitals on the TF cations. This will occur if the compound can be appropriately doped with aliovalent ions or alternatively reduced chemically. 

When BaTiOj loses oxygen, the resistivity falls considerably. The reduced materials show semiconducting/insulating behaviour until the composition approaches 

The electrons on the Ti (d ) cations are allocated to the conduction band, giving rise to itinerant electron metallic conductivity. 

The phase LaNi03, with Ni B-site cations, has rhombohedral symmetry of the LaA103 type and is a typical Pauli paramagnetic metal. The low-spin (LS) d ion has a nominal electron configuration of e , and the partly filled e band, containing one d-electron, allows for metallic conduction. If the La cation is replaced by other smaller lanthanoids, on moving from La towards Lu, there is a change from metallic 

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