Effect of Nb5+ doping on the microstructure and conductivity of Li1.125Ta0.875Zr0.125SiO5 electrolyte

•Nb5+-doped Li1.125Ta0.875-xNbxZr0.125SiO5 ceramic electrolytes were prepared.•The microstructure and electrochemical properties of ceramics were discussed in detail.•0.1875 mol Nb5+-doped sample had the best conductivity of 3.521 × 10-5 S/cm at 25 °C.•The ionic conductivity of the 0.1875 mol Nb5+-doped sample is an order of magnitude higher than the original one.•Li1.125Ta0.6875Nb0.1875Zr0.125SiO5 ceramics have the potential used in solid electrolytes.