Orbitally-driven Peierls state in spinels
  We consider the superstructures, which can be formed in spinels containing on B-sites the transition-metal ions with partially filled t2g levels. We show that, when such systems are close to itinerant state (e.g. have an insulator-metal transition), there may appear in them an orbitally-driven Peierls state. We explain by this mechanism the very unusual superstructures observed in CuIr2S4 (octamers) and MgTi2O4 (chiral superstructures) and suggest that similar phenomenon should be observed in NaTiO2 and possibly in some other systems. 
D. I. Khomskii and T. Mizokawa