The lithium fast-ion conductor, Li1+xAlxTi2-x(PO4)(3) (LATP) has been modified via changes in stoichiometry during the processing steps. The resultant changes have been followed using Al-27 MAS NMR, X-ray powder diffraction and impedance spectroscopy. The most important changes were those of the form Li1.3+4yAl0.3Ti1.7-y(PO4)(3). It was possible to remove the AlPO4 phase (both tridymite and berlinite polymorphs), as monitored by X-ray diffractograms and Al-27 NMR spectra. Consequently, these changes appear to result in increased grain boundary conductivity of the LATP material.