Peculiarities of ionic conduction in Li0.5 − yNayLa0.5Nb2O6 system at high temperatures

Pure perovskite structure Li0.5 − yNayLa0.5Nb2O6 compounds with y values of 0, 0.1, 0.2, 0.3, 0.4, 0.43, 0.48 and 0.5 have been synthesized. Ceramics of these compounds were studied by X-ray diffraction and impedance spectroscopy in the frequency range of 10 Hz to 10 GHz and temperature interval from 300 K to 800 K. The linear increase of the lattice parameters with increasing temperature causes the wider opening of bottleneck for lithium migration which leads to ionic conductivity increase. The temperature dependencies of the studied compounds conductivity were described by modified Vogel-Fulcher-Tammann equation. The influence of Li+ to Na+ substitution to the lithium ionic transport is also analysed. On one hand the lattice parameters of Li0.5 − yNayLa0.5Nb2O6 were found to be bigger for compound with higher sodium concentration, which also increases their ionic conductivity. On the other hand the increase of y leads to decrease of charge carriers, which are lithium ions, concentration. Consequently the conductivity rapidly decreases.