With the aim of producing all-solid-state electrochromic mirrors, La 0.67–xLi 3xTiO 3 (LLTO) and the WO 3 were prepared by electron beam deposition. The LLTO (with x = 0.11) powder was synthesized by thermally ball-grinding method and the Li + ionic conductivity of the LLTO ceramic targets was found to be of ca. 3.25 × 10 –3 S/cm. Using LLTO targets for e-beam evaporation, 300 nm-thick films with the Li + ionic conductivity of 5.50 × 10 –5 S/cm were deposited. Combining LLTO films with WO 3/ITO and LiMn 2O 4 layers, all-solid-state electrochromic mirrors with a laminar structure of Al/LiMn 2O 4/LLTO/WO 3/ITO were prepared. The reversible reflectance of the mirrors was well controlled by applying polarized potentials onto the ITO electrode. The obtained results suggest useful applications for electrochromic windows working as a smart reflectance mirror that can be used for auto rear-view mirrors.
Electrochromism is a topic that has attracted a great deal of interest from researchers because of its potential application in various areas, such as photonics, optics, electronics, architecture, etc. Electrochromic (EC) properties can be found in almost all the transition-metal oxides and their properties have been investigated extensively in the last decades [
Recently, many works [
In this work, the e-beam evaporation method was also used for deposition of LLTO thin films. The solid-state electrolyte LLTO films were used in WO3-based ECD devices working as all-solid-state electrochromic mirror mirrors. The performance of the electrochromic mirrors was also presented.
The La0.67−xLi3xTiO3 crystalline powder was synthesized by ball grinding method according to the following reaction:
where the values of x was chosen as 0.11, with this value the ionic conductivity was the best one as reported in [
The structure of LLTO films was characterized by X-ray diffraction (XRD) patterns recorded by a Siemens D-5000 X-ray diffractometer with Cu-Ka radiation. The morphology and cross-section of the LLTO thin films were investigated by field emission scanning electron microscopy (FE-SEM). The ionic conductivity of thin films was characterized on Auto. Lab Potentiostat-PGS30 with a FRA-2 impedance spectra technique. Optical measurement was carried-out on a Jasco V-570 photospectrometer.
where l is wavelength of the X-ray used, b the peak width of half height in radians and q the Bragg angle of the considered diffraction peak [
From impedance spectra measurements, the ionic conductivity of the ceramic LLTO targets was found to be of 3.25 ´ 10−3 S/cm that consists with the value reported in [
where d and S are the thickness (300 nm) and electrode area (0.25 cm2) on the LLTO thin film, respectively.
From the equivalent circuit schema fitting with the experimental curve, R2 was found to be of 2.18 W. In this case, the ionic conductivity of the films determined from formula (3) is as large as s = 5.50 ´ 10−5 S/cm, that is comparative with the conductivity of the LLTO thin films prepared by the pulsed laser deposition [
As-deposited LLTO thin films have slightly yellow color in visible range.
For the LWM mirror, the in-situ reflectance spectra, obtained during coloration and bleaching at a polarized potential of −1.5 V and +1.5 V, respective to the ITO electrode, are given in
performance, the reflectance of the LWM mirror is determined mainly by the coloration (or absorption) of the WO3 electrochromic layer.
The electrochromic performance of the WO3 electrode in LiClO3 + PC was described by cathodic reactions [
Thus in the LWM device the coloration/bleaching can be attributed to the insertion/extraction of Li+ ions in/out WO3 layer from LiMn2O4 through the solid LLTO electrolyte. The fact that the reflectance of the LWM mirror can be controlled by applying a polarized voltage onto ITO electrode proves that all-solid-state electrochromic devices can be utilized for fabrication of auto rear-view mirrors. Using these mirrors, the drives can prevent accidents which may be caused by radiating from the headlamp of the behind cars.
By using thermally ball-grinding method, submicro-structured La0.67−xLi3xTiO3 (with x = 0.11) powder was synthesized for the targets in e-beam deposition of the LLTO films. The best ionic conductivity of the films possesses a value as high as 5.50 ´ 10−5 S/cm. All-solid-state electrochromic devices of a laminar structure of Al/LiMn2O4/LLTO/ WO3/ITO were prepared. The reversible reflectance of the device was well controlled by polarization of potentials applied onto the ITO electrode. The obtained results suggest useful applications for electrochromic windows working as a smart reflectance mirror that can be used for auto rear-view mirrors.
This research was funded by the operational fund for science and technology of Hanoi Pedagogical University 2, under grant number C2015-18-05.
Trong, L.D., Dinh, N.N. and Thanh, D.H. (2016) Preparation and Characterization of La0.67−xLi3xTiO3 Solid-State Electrolyte Used for Electrochromic Mirrors. Materials Sciences and Applications, 7, 702-709. http://dx.doi.org/10.4236/msa.2016.711056