Because of the inconsistent results of indentation on a rough, fractured surface of LLZO, we elected to polish the samples to obtain more consistent results. The LLZO samples were polished for indentation using 400 and 800 grit silicon carbide sandpaper (Allied) for 2 and 5 min, respectively, followed by 6 µm and 1 µm diamond suspensions (Ted Pella) for 10 and 5 min, respectively. All the suspensions used glycol as the solvent. Polishing was performed by hand on an 8-inch-diameter polishing wheel (Buehler) at 150 rpm. The sample was washed in ethanol after each suspension step.