Effects of annealing temperature on structure and opt-electric properties of ion-conducting LLTO thin films prepared by RF magnetron sputtering

▶ Lithium lanthanum titanate (LLTO) thin films are seldom studied due to its reaction with lithium which prohibited its use in lithium batteries but may fit the requirement of electrolyte in all-solid-state electrochromic devices. In this paper, highly transparent and ion-conductive LLTO thin films were prepared by radio-frequency (RF) magnetron sputtering. The effects of annealing temperatures on the structural, morphological, optical and electrochemical properties were studied. It is found that after annealing at 300 °C for 2 h, the structural, microstructural, optical and electrochemical properties were improved greatly. Highly transparent and ion-conducting lithium lanthanum titanate (LLTO) thin films were deposited on ITO/glass substrates by RF magnetron sputtering. The results of X-ray diffraction indicate that the as-prepared LLTO thin films and the annealed ones at temperatures up to 300 °C are amorphous; however, crystal phases, including La 0.56Li 0.33TiO 3 and other unexpected ones, appear on the annealed films at 400 °C. SEM and AFM results show that the prepared films turn to be denser, smoother and more uniform up to 300 °C while the deteriorative results come out following the further enhancement of annealing temperature. Further characterization of opt-electric properties of the prepared films reveals that the annealed ones at 300 °C own the best optical transmittance of 85% and the highest room temperature ionic conductivity of 5.25 × 10 −5 S cm −1, which are suitable for the application as an electrolyte of all-solid-state electrochromic devices.