Densification of Na4Zr2Si3O12 (NZS) solid electrolytes was performed by dispersing TiO2 (0.8-5.9 wt. %, corresponding to 5-30 mol%) in NZS powders prior to sintering at 1200 degrees C. Increases in pellet density, from ca. 65 to 94% of the theoretical (X-ray density) value, and in electrical conductivity from 10(-7) to 10(-6) S/cm at 50 degrees C were observed for small additions of TiO2, which acts as a sintering aid. AC impedance spectroscopy reveals that the enhancement is not a bulk effect but instead is associated with a reduction in inter-granular constriction resistances within porous NZS ceramics. The presence of adsorbed water species in NZS powders prepared via a sol-gel route is found to have a dramatic effect on the conductivity enhancement.