Oxygen-deficient tetragonal tungsten bronzes ceramics with general formula Ba2NdTi2+xNb3-xO15-x/2 (0 <= x <= 1) have been prepared by low temperature solvothermal synthesis with final firing of ceramics at 1100-1300 degrees C in air. Rietveld refinement of X-ray powder diffraction (XRD) and neutron powder diffraction (ND) data at room temperature of Ba2NdTi3Nb2O14.5 shows that Ba and Nd are ordered on the 15-coordinate and 12-coordinate sites, respectively, Ti and Nb are disordered nonrandomly over the two octahedral sites, and oxygen vacancies locate preferentially in the coordination sphere of Nd and Ti/Nb(2) atoms. Variable frequency impedance measurements show that samples are poor electronic conductors with activation energies similar to 0.8-1.7 eV, conductivities similar to 1 x 10(-5) S cm(-1) at similar to 725 degrees C and with some evidence of oxide ion conduction at high x values. Composition dependence of the dielectric properties shows a transition from classic ferroelectric behavior with Ba2NdTi2Nb3O15 to a relaxor-like behavior with Ba2NdTi3Nb2O14.5. At intermediate compositions, both a first-order phase transition and relaxor-like behavior are observed.