Room temperature elastic moduli and Vickers hardness of hot-pressed LLZO cubic garnet

Cubic garnet Li6.24La3Zr2Al0.24O11.98 (LLZO) is a candidate material for use as an electrolyte in Li-Air and Li-S batteries. The use of LLZO in practical devices will require LLZO to have good mechanical integrity in terms of scratch resistance (hardness) and an adequate stiffness (elastic modulus). In this paper, the powders were fabricated by powder processing of cast ingots. All specimens were then densified via hot pressing. The room temperature elastic moduli (Young's modulus, shear modulus, bulk modulus, and Poisson's ratio) and hardness were measured by resonant ultrasound spectroscopy, and Vickers indentation, respectively. For volume fraction porosity, P, the Young's modulus was 149.8 +/- A 0.4 GPa (P = 0.03) and 132.6 +/- A 0.2 GPa (P = 0.06). The mean Vickers hardness was 6.3 +/- A 0.3 GPa for P = 0.03 and 5.2 +/- A 0.4 for P = 0.06.