Study On Solid-State Electrolyte Lithium Lanthanum Titanate Thin Films Deposited By Magnetron Sputtering

Electrolyte is one of the most important parts of electrochromic devices. The ionic conductivity of bulk lithium lanthanum titanate (LLTO) is higher than 10-3 S cm-1, which makes it as one of the highest solid-state electrolyte in the literatures. But the ionic conductivity of the LLTO thin films is much lower than that of bulk LLTO materials, typically the order of 10-6 S cm-1. So, it is one of the hot point of the researches to develop inorganic solid-state electrolyte thin films with high ionic conductivity and optical transmissionBased on the above reason, the LLTO ceramic target was prepared by solid-state reaction and LLTO thin films were sputtered on ITO/glass substrates. The effects of annealing temperature and time on the properties of LLTO thin films were also studied. The main results and conclusions are shown as below:1. The Li0.33La0.56TiO3 target was prepared by solid-state reaction at 1200℃for 10 h and the ionic conductivity was up to 1.0×10-3 S cm-1;2. Amorphous LLTO thin films were deposited by RF magnetron sputtering under substrate temperatures from 50 to 300℃and the transmission in visible spectrum was more than 75%; With the increase of substrate temperature, the films became denser and smoother, the root mean square roughness declined and the ionic conductivity improved from 7.1×10-6 to 8.6×10-6 S cm-1. All of these may be resulted from that when the substrate temperature increased, the surface diffusion was strengthened, then the shallow effects weakened;3. The LLTO thin films were annealed at different temperatures and times, the effects of annealing temperatures on the structural, morphological, optical and electrochemical properties were studied. The films both the as-deposited and annealed below 400℃were amorphous, but slight crystallization after annealed at 400℃. With the increase of annealing temperature below 400℃, the ionic conductivity enhanced for the increase of pre-exponential due to the densification of thin films and increase of jump distance and vibration frequency of lithium ion, although the activation energy kept as a constant of 0.35 eV. The transmission of film annealed at 300℃was approximately 85% in visible spectrum and the ionic conductivity was 5.25×10-5 S cm-1 at room temperature. All of these characteristics indicate that LLTO thin film is suitable for applications as the electrolyte layer of all-solid-state electrochromic devices.