Tuning the Li diffusivity of poor ionic conductors by mechanical treatment:: High Li conductivity of strongly defective LiTaO3 nanoparticles

Lithium tantalum oxide, LiTaO3, with an average particle size in the mu m range is known as a very poor Li ion conductor. It is shown here that its Li conductivity can be drastically increased by ball milling. The so-obtained nanostructured powder with an average particle size of about 20 urn shows a dc conductivity, sigma(dc), of about 3 x 10(-1) S cm(-1) at T = 450 K (sigma T-dc = 1.4 x 10(-3) S cm(-1) K) which is about 5 orders of magnitude larger than that of the corresponding microcrystalline powder at the same temperature. The activation energy E-A is reduced by about one-third, i.e., it decreased from E-A = 0.90(1) eV to about E-A = 0.63(1) eV. The effect of different milling times on the ionic conductivity is studied. Furthermore, the thermal stability of the nanocrystalline materials against grain growth has been examined by in situ impedance spectroscopy. Interestingly, the Li conductivity of a sample milled for 16 h does not change much even when the material is exposed to about 700 K for several hours. Moreover, the Li self-diffusion in the nanostructured as well as the coarse grained materials has been investigated by various solid-state Li-7 NMR techniques.