  We report 7Li NMR studies of V-substitution effects on spinel oxide
superconductor LiTi2O4 (Tc = 13.4 K). In LiTi2-xVxO4 (x = 0-0.4), the V
substitution for the Ti site suppressed the relative volume fraction of
superconductivity faster than Tc. From the observation of fairly homogeneous
enhancement in a 7Li nuclear spin-lattice relaxation rate, we conclude that the
V substitution changes electron correlation effects through electron carrier
doping from quarter electron filling 3d0.5 to 3d1.5 and then the
antiferromagnetic correlation emerges.
