Inter-grain Li+ conduction in Sc and Y doped LATP compounds

Low value of grain boundary conductivity in Li-NASICON materials is an important limitation that needs to be overcome. Inter-grain conduction of Li + ions in Li1·3Al0.3-xScxTi1.7(PO4)3 (LASTP) and Li1·3Al0.3-xYxTi1.7(PO4)3 (LAYTP) (where x = 0.01 and 0.07) samples is investigated. The samples, prepared by solid state reaction method, were characterised by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) techniques. Electrochemical Impedance Spectroscopy (EIS) was performed in the frequency range of 20 MHz to 1 Hz, and temperature range of 20 °C–100 °C. The grain boundary impedance and capacitance was found to vary with an external dc bias voltage. Higher grain boundary conductivity was found for sample containing higher yttrium concentration. Effect of space charge on grain boundary conductivity is evaluated in light of two competing models.