Preparation of compact Li-doped Y2Ti2O7 solid electrolyte

Three series of solid electrolytes were prepared with the nominal compositions of (Y2 − xLi3x)Ti2O7 (Y3LT), (Y2 − xLix)Ti2O7 − x (YLT) and Y2 − xTi2O7 − 3x/2 (YT) with x = 0.040 − 0.11. Comparing the unit cell a-axis of the YLT with that of YT, the latter is shorter with the same amount of x. This indicates a successful substitution of the Li ion into the Y site of Y2Ti2O7. However, both Y3LT and YLT have exactly the same unit cell a-axis length with the same amount of x so that the solid solution formed probably has the same formula, (Y2 − xLix)Ti2O7 − x, in which only one Li ion is substituted into the Y site. Extra Li2O added in the Y3LT is probably acting as a self flux to lower the melting point of the mixture. As a result, materials become more compact and grains grow bigger. One compound of Y3LT with x = 0.060 has a total conductivity of 4.3(4) × 10− 4 S⋅cm− 1 at 700 °C. Adding Li2O as a flux and carefully controlling the heat treatment history, compact sample of Y3LT with a relative density higher than 90% was obtained at a temperature as low as 1150 °C. Its ionic conductivity is comparable to one Y2Ti2O7 prepared at 1600 °C with a conductivity reported as 2.30 × 10− 4 S⋅cm− 1.