A SECOND-ORDER JAHN-TELLER DISTORTION IN THE SOLID: THE PHASE TRANSITION IN VS,*

Abstract:

Tight-binding band structure calculations have been performed on both the NiAs (hexagonal) and MnP (orthorhombic) structures of vanadium sulfide VS. A band folding procedure is used to generate the electronic structure of the hexagonal phase in orthorhombic symmetry and allows one to understand the reasons for the NiAs to MnP structural distortion as vanadium vacancies in VS are filled. When a critical electron filling of the metal d bands is reached, a second-order Jahn-Teller mixing operates to stabilize the MnP structure and induces the concomitant formation of metal-metal zig zag chains. The resulting “dip” in the density of states at the Fermi level is analyzed in conjunction with the experimentally observed changes in conductivity, and Knight shift measurements. Finally, the computed relative stability of the two structures for different metal monosulfides is shown to agree qualitatively with the experimental data available. 

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