BAND ANALYSIS OF THE HIGH-TC PROSPECTS FOR CANIN AND RELATED PEROVSKITE-TYPE NITRIDES

Half-filled sigma* bands, a distinctive characteristic of parent compounds for cuprate and bismuthate high-T(c) superconductors, are utilized as an electronic ''fingerprint'' to identify possible high-T(c) candidates among perovskite-type nitrides such as Ca3BiN and CaNiN. Band calculations for CaNiN confirm earlier results where the sigma* bands lie below E(F), leaving conduction electrons with pi* rather than sigma* character. Model tight-binding calculations show that this sigma*-pi* reversal is due to the linear-chain feature of the CaNiN structure rather than the proximity of Ca(3d) bands. The sigma* band survives intact in a hypothetical CaNiN2 phase that contains NiN2 planes. However, this band is empty rather than half filled, thus providing an opportunity for some creative materials synthesis. Because of this generally unfavorable combination of structural, electronic, and compositional deficiencies, it is concluded that nitrides are less-than-ideal candidates for high-T(c) superconductivity.