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Spin fluctuation and the transport mechanism in the spinel systems Li x Mg 1Ϫx V 2 O 4 and Li x Zn 1Ϫx V 2 O 4 with 0рxр1 have been studied through measurements of x-ray diffraction, electrical resistivity, thermoelectric power, magnetization, and nuclear magnetic resonance. These compounds range from being antiferromagnetic and insulating for MgV 2 O 4 ͑Mott type͒ accompanied with a structural transition to the metallic state of LiV 2 O 4 with no magnetic order. The metal-insulator transition may be of Anderson type and occurs in the vicinity of x c ϭ0.4. The coherence length of the wave function of hole carriers in the variable-range-hopping regime has a critical exponent Ϫ1.3 against ͉xϪx c ͉. The metallic phase above x c may have two kinds of carriers from dynamic mixed valence state of V 3ϩ and V 4ϩ. Based on the magnetic susceptibility and relaxation analyses, metallic compounds may be considered to be highly correlated electron systems with a low degeneracy temperature or large mass enhancement. On the other hand, insulators have short-range ordered spin correlation and/or superparamagnetic effects. At low temperatures, an antiferromagnetic phase is realized for x р0.05 and a spin-glass phase originating from the frustration inherent in the spinel B lattice appears in the region of 0.07рxр0.7. The latter phase is enhanced for concentrations slightly less than x c. ͓S0163-1829͑97͒02931-7͔

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