Hot-pressing at 1050 degrees C lead to near theoretical density (similar to 98% relative density) tetragonal LLZO. The total conductivity value for dense tetragonal LLZO is similar to 2.3 x 10(-5) S cm(-1). This is the highest reported value for tetragonal LLZO. This vast improvement in total conductivity is a result of the higher density achieved as a result of hot-pressing compared to conventional solid-state sintering. The value of the Li-ion lattice conductivity for dense tetragonal LLZO is 1.1 x 10(-4) S cm(-1). The microstructure of dense tetragonal LLZO consist of twins within the grains. It is suggested that the presence of twin boundaries adds a significant contribution to the total resistance. Published by Elsevier B.V.