Lithium conductivity and lithium diffusion in NASICON-type Li1+xTi2-xAlx(PO4)3 (x=0; 0.3) prepared by mechanical activation

LiTi2(PO4)(3) (LTP) and Li1.3Al0.3Ti1.7(PO4)(3) (LATP) (S. g. R-3c) have been prepared using conventional ceramic and mechanical activation (MA) methods. It has been shown that preliminary mechanical activation of initial mixtures leads to different nature and amount of dielectric admixtures in the final product after heat treatment at 800-1000 degrees C as compared with ceramic method. Transport properties of as prepared materials have been studied by lithium ionic conductivity at d.c. and a.c. (complex impedance method), and Li-7 NMR spin-lattice relaxation rate T-1(-1) measurements. Lithium ionic conductivity of mechanochemically prepared LTP and LATP was characterized by significant reduction of grain boundary resistance, especially for LTP, while the bulk conductivity and Li ion diffusion does not noticeably change. The activation energy of bulk conductivity and Li ion diffusion, i.e. short-range motion, appeared to be almost the same for all samples and was equal to similar to 0.20 eV. On contrary, the activation energy of d.c.-conductivity, i.e. long-range Li ion motion decreases from similar to 0.6 eV for ceramic samples to similar to 0.4 eV for samples prepared via mechanochemical route. It was proposed that MA leads to formation of nano-particulate high-conductive grain boundaries both in LTP and LATP.