Electronic band structure calculations of the MNX (M = Zr, Ti; X = Cl, Br, I) system and its superconducting member, Li-doped {beta}-ZrNCl
- Brookhaven National Lab., Upton, NY (United States). Physics Dept.
Electronic band structure calculations have been performed for {beta}-ZnNCl, {beta}ZnNBr, {alpha}-ZrNBr, {alpha}-ZrNI, and {alpha}-TiNX (X = Cl, Br, I) using the extended Hueckel method. These calculations reveal that n-doped {beta}-ZrNCl has a single narrow band at the Fermi level which is stabilized by overlap of 4dz{sup 2} orbitals on zirconium with respect to the remainder of the conduction band states. This band shows only a small degree of dispersion and can essentially be described as a localized Zr-Zr bond when the carrier concentrations are low. The calculated band structure is consistent with the experimental observations of activated carrier transport, and an indirect optical band gap in {beta}-ZrNCl and {beta}ZrNBr. A simple picture is presented which describes a mechanism for strong electron-phonon coupling in the {beta}-ZrNX structure, suggesting that {beta}-Li{sub x}ZrNCl is a classical BCS superconductor. This localized 4dz{sup 2} band at the Fermi level is absent in the electronic band structures of {alpha}-ZrNX and {alpha}-TiNX compounds. The dispersion relations for these compounds show a direct optical band gap, as observed experimentally. The absence of significant metal-metal bonding in {alpha}-MNX compounds implies that n-doping will be more difficult to achieve in compounds adopting this structure. The relative stability of {alpha}- and {beta}-polymorphs is also discussed.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC02-76CH00016
- OSTI ID:
- 651114
- Journal Information:
- Journal of Solid State Chemistry, Vol. 138, Issue 2; Other Information: PBD: Jul 1998
- Country of Publication:
- United States
- Language:
- English
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