Low temperature cubic garnet-type Li7La3Zr2O12 was obtained by annealing the tetragonal Li7La3Zr2O12 at 450 degrees C for 20 h in air. The cubic phase was not observed by annealing at 450 degrees C in oxygen and argon atmospheres. The phase transition of the tetragonal to cubic phase was reversible in air and could be explained by CO2 absorption of around 2.5 wt.%. The low temperature cubic Li7La3Zr2O12 had a low bulk ionic conductivity of 1.3 x 10(-6) S cm(-1) at 25 degrees C, which is lower than those of the tetragonal Li7La3Zr2O12 (3.3 x 10(-6) S cm(-1)) and high temperature cubic phases (5.8 x 10(-4) S cm(-1)). (C) 2012 Elsevier B.V. All rights reserved.