Study of structure and conductivity of Li3/8Sr7/16-3x/2LaxZr1/4Nb3/4O3 solid electrolytes

Li3/8Sr7/16-3x/2LaxZr1/4Nb3/4O3 (x = 0, 0.05, 0.10, 0.15, 0.20) were synthesized using the conventional solid-state reaction method. In order to increase the vacancy concentration, La3+ was doped on the Sr2+ site. Crystal structures of doped samples were characterized by X-ray diffraction. Except, perovskite-type Li3/8Sr7/16-3x/2LaxZr1/4Nb3/4O3 (x = 0, 0.05, 0.10, 0.15) samples were fabricated by heat treatment at 1250 °C, 1275 °C, 1275 °C and 1275 °C, respectively, for 15 h. Lattice sizes decreased with the increase of doping amounts because of the smaller ion radius of La3+ compared to that of Sr2+. Ionic conductivities of the samples were measured by AC impedance spectroscopy. The results showed that the ionic conductivity increases at first and then decreases with raising doping amounts and sintering temperatures. So the optimized composition Li3/8Sr7/16-3x/2LaxZr1/4Nb3/4O3 (x = 0.05) sintered at 1275 °C was selected with the highest total conductivity of 3.33 × 10−5 S cm−1at 30 °C and an activation energy of 0.27 eV. Additionally, potentiostatic polarization test was used to evaluate the electronic conductivity. The optimal composition Li3/8Sr7/16-3x/2LaxZr1/4Nb3/4O3 (x = 0.05) as a possible Li-ion conducting solid electrolyte has an electronic conductivity of only 8.39 × 10−9 S cm−1.