The effect of Al and Li concentration on the formation of cubic garnet of nominal composition Li7La3Zr2O12 was investigated. It was determined that at least 0.204 moles of Al is required to stabilize the cubic phase. It was observed for the cubic phase (stabilized by the addition of Al) that as Li content was increased from 6 to 7 moles it transformed to a tetragonal phase. Additionally, powders of cubic Li6.24La3Zr2Al0.24O11.98 were hot-pressed at 1000 degrees C and 40 MPa. The hot-pressed material had a relative density of 98%. The room temperature total ionic conductivity of the hot-pressed material was 4.0 x 10(-4) S/cm and the electronic conductivity was 2 x 10(-8) S/cm. (C) 2011 Elsevier B.V. All rights reserved.