A systematic study was carried out to explore the impact of sintering temperature on the densification, phase formation, microstructure, crystallinity, and ionic conductivity of Li1.5Al0.5Ti1.5(PO4)(3) (LATP). There is clear evidence that a) both the total conductivity and bulk conductivity increase with increasing sintering temperature, and b) the phase purity, crystallinity and compositional homogeneity range of LATP are the key factors that influence the bulk ionic conductivity. Furthermore, the influence of a sintering aid (Li2B4O7) on the microstructure and ionic conductivity of LATP was probed. The Li2B4O7 improved the microstructural parameters of the LAW electrolyte and thus remarkably reduced the grain boundary resistance of the pristine LATP from 3500 Omega.cm to 1500 Omega.cm. The sintering aid Li2B4O7 did not influence the stoichiometry or the long-range order of LAW but rather acted as an ion-conducting bridge between the LAW grains facilitating the Li-ion transport.