Preparation and electrical properties of garnet-type Li6BaLa2Ta2O12 lithium solid electrolyte thin films prepared by pulsed laser deposition

The growth of Li-ion conducting Li6BaLa2Ta2O12 garnet-type thin films by pulsed laser deposition (PLD) is reported. Li6BaLa2Ta2O12 was synthesized as target material by a high temperature solid-state reaction. Thin films were grown on MgO(100) by ablation of the respective bulk target material consisting of Li6BaLa2Ta2O12 with 5 mol% excess of Li2O to compensate lithium loss during thin film growth. X-ray diffraction revealed a garnet-type structure of the prepared thin films. The bulk material showed electrical conductivity of up to σ = 5.0 ⋅ 10− 5 S cm− 1 at 25 °C, whereas the Li6BaLa2Ta2O12 garnet-type films exhibit a lower conductivity of σ = 2 ⋅ 10− 6 S cm− 1 at 25 °C, which is comparable to the ionic conductivity of LiPON being about σ = 2 ⋅ 10− 6 S cm− 1 at the same temperature. The activation energy Ea of bulk and thin film samples results in 0.44 eV and 0.42 eV, respectively, as determined by temperature-dependent conductivity measurements. Ohara glass-ceramic was successfully protected against reduction by deposition of a thin garnet-type film on top of the glass ceramic. The partial electronic conductivity of the bulk material was determined by the Wagner–Hebb-polarization technique. The electronic partial conductivity took values between σel = 2.87 ⋅ 10− 13 S cm− 1 and σel = 3.47 ⋅ 10− 10 S cm− 1 in the range of the polarization voltage U = 2.8 V to U = 4.3 V, resulting in low electronic transference numbers between tel = 5.74 ⋅ 10− 9 and tel = 6.76 ⋅ 10− 6.