Orbital molecules in vanadium oxide spinels

X-ray scattering and magnetization measurements have been used to explore the extent of orbital molecule formation in a variety of AV(2)O(4) vanadium oxide spinels. Zn doping suppresses the long-range order of trimer-tetramer pairs that occurs in GaV2O4, but disordered orbital molecules are found across most of the ZnxGa1-xV2O4 series (0.06 <= x < 0.875). Orbital molecules are not observed in the ground states of ZnV2O4, MgV2O4, or LiV2O4 but are likely present in Li0.5Ga0.5V2O4, an analog of the former two materials. The ratio of observed to ideal values of the V-V nearest-neighbor distance has been used to rationalize these observations.