Spinel vanadates possess rich physics arising from the interaction among spin,orbital and lattice degrees of freedom.We report the dielectric properties of polycrystalline Fe1.8V1.2O4.A thermally activated dielectric relaxation appeared in low temperature due to the inhomogeneous conductivity between grains and grain boundaries.We found an artificial ferroelecticity in this sample.An abnormal frequency-independent dielectric peak appeared at room temperature when the samples were measured during warming in ambient air.However,this peak disappeared in the following cooling process.By dielectric frequency spectrum and equivalent circuit analysis in detail,we found the sample had a surface layer in warming but not in cooling process.We also confirmed that this surface layer was induced by the adsorption of water,which is responsible for the dielectric peak. Spinel vanadates posse rich physics arising from the interaction among spin, orbital and lattice degrees of freedom. We report the dielectric properties of polycrystalline Fe1.8V1.2O4.A thermally activated dielectric barrier occurred in low temperature due to the inhomogeneous conductivity between grains and grain boundaries.We found an artificial ferroelecticity in this sample. An abnormal frequency-independent dielectric peak was at room temperature when the samples were measured during warming in ambient air. Even though this peak disappeared in the following cooling process.By dielectric frequency spectrum and equivalent circuit analysis in detail, we found the sample had a surface layer in warming but not in cooling process. We also confirmed that this surface layer was induced by the adsorption of water, which is responsible for the dielectric peak.