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Zusammenfassung:
We develop a microscopic theory for the charge ordering (CO) transitions in the spinels AlV 2 O 4 and LiV 2 O 4 (under pressure). The high degeneracy of CO states is lifted by a coupling to the rhombohedral lattice deformations which favors a transition to a CO state with inequivalent V(1) and V(2) sites forming Kagomé and trigonal planes, respectively. We construct an extended Hubbard-type model including a deformation potential which is treated in an unrestricted Hartree–Fock approximation and describes correctly the observed first-order CO transition. We also discuss the influence of associated orbital order. Furthermore, we suggest that due to different band fillings AlV 2 O 4 should remain metallic while LiV 2 O 4 under pressure should become a semiconductor when charge disproportionation sets in.
