Charge ordering in the spinels AlV2O4 and LiV2O4
Abstract
We develop a microscopic theory for the charge ordering (CO) transitions in the spinels AlV2O4 and LiV2O4 (under pressure). The high degeneracy of CO states is lifted by a coupling to the rhombohedral lattice deformations which favors transition to a CO state with inequivalent V(1) and V(2) sites forming Kagom\'e and trigonal planes respectively. We construct an extended Hubbard type model including a deformation potential which is treated in 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 AlV2O4 should remain metallic while LiV2O4 under pressure should become a semiconductor when charge disproportionation sets in.
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