Structure and Conductivity of Li3/8Sr7/16−xAxZr1/4Nb3/4O3 (A = Ca, Ba) Li-ion Solid Electrolytes

Li3/8Sr7/16−xAxZr1/4Nb3/4O3 (A = Ca, Ba) ceramics were prepared by the conventional solid-state reaction method. The structures of prepared ceramic materials changed from cubic perovskite to tetragonal tungsten bronze with increasing barium (Ba) content as indicated by the x-ray diffraction (XRD) patterns. Li3/8Sr7/16−xBaxZr1/4Nb3/4O3 (x = 0.05, 0.10) samples are mixtures of perovskite and tetragonal tungsten bronze phases. Calcium ions (Ca2+) can partially occupy the Sr sites, and thus the cubic perovskite structure remains intact. However, an unknown phase could form because of a complete substitution of Ca for Sr; the ionic conductivity measured by the alternating-current impedance spectra of samples decreases with increasing Ba and Ca content. Parent Li3/8Sr7/16Zr1/4Nb3/4O3 exhibits the highest ionic conductivity of 1.23 × 10−5 S cm−1 at 25°C. Additionally, a half cell of LiFePO4/Li performed well in charge–discharge experiments, retaining a discharge capacity of 87.9 mAhg−1 after 300 cycles when Li3/8Sr7/16Zr1/4Nb3/4O3 was selected as the solid electrolyte separator.