For data acquisition, Qtegra software provided by the manufacturer was used. Sample digestion was performed using a borax fusion: 5-10 mg sample were mixed with 0.5 g borax and heated to 1000 °C for 5 h. The solidified fusions were dissolved at 70 °C using a HCl/HF/H2O mixture (10 m% HCl, 0.8 m% HF). A univariate calibration using certified single element ICP-standard solutions was used for signal quantification. For the correction of instrumental drifts and variations in sample introduction, Eu was added to all measured solutions and used as internal standard. More detailed information on the procedure used for the bulk analysis of LLZO via ICP-OES can be found elsewhere.