Nb-doped BaTiO₃ solid solutions of general formula, BaTi_1−5xNb_4xO₃ prepared by two methods, solid state reaction at 1500 °C and sol–gel synthesis from high purity alkoxide precursors with final heat treatment at 900 °C, form over the range 0 ≤ x ≤ 0.055(5). Permittivity measurements demonstrated the difficulty in obtaining high quality, electrically-homogeneous samples by solid state reaction, even though samples were nominally phase-pure by X-ray powder diffraction. A partial phase diagram has been constructed showing the transitions between tetragonal, cubic and hexagonal polymorphs as a function of composition. Pellets derived from sol–gel samples and sintered at 900 °C were highly insulating, with an activation energy of ∼1.5 eV. Under these firing conditions, there was no evidence of electronic compensation, and semiconductivity, on doping BaTiO₃ with Nb.