Thin film batteries based on solid electrolytes having a garnet-structure like Li7La3Zr2O12 (LIZ) are considered as one option for safer batteries with increased power density. In this work we show the deposition of Ta- and Al-substituted LLZ thin films on stainless steel substrates by r.f. magnetron sputtering. The thin films were characterized by XRD, SEM and time-of-flight-secondary ion mass spectrometry (ToF-SIMS) to determine crystal structure, morphology and element distribution. The substrate temperature was identified to be one important parameter for the formation of cubic garnet-structured LIZ thin films. LLZ formation starts at around 650 degrees C. Single phase cubic thin films were obtained at substrate temperatures of 700 degrees C and higher. At these temperatures an interlayer is formed. Combination of SEM, ToF-SIMS and XRD indicated that this layer consists of gamma-LiAlO2. The combined total ionic conductivity of the gamma-LiAlO2 interlayer and the LIZ thin film (perpendicular to the plane) was determined to be 2.0 x 10(-9) S cm(-1) for the sample deposited at 700 degrees C. In-plane measurements showed a room temperature conductivity of 1.2 x 10(-4) S cm(-1) with an activation energy of 0.47 eV for the LLZ thin film. (C) 2016 Elsevier B.V. All rights reserved.