The optical properties of lithium tungsten bronze single crystals and thin films for electrochromic window device applications
The optical and structural properties of rf sputter deposited thin films of Li[sub x]WO[sub 3], prepared by insertion of lithium either electrochemically or by sputter depositing lithium aluminum borate (LABO) or lithium carbonate (LCO) were studied as a function of lithium concentration. Single crystals of Li[sub x]WO[sub 3] were studied. The results were compared with results for sodium tungsten bronze (Na[sub x]WO[sub 3]) single crystals. From the optical data, physical parameters such as effective mass and intrinsic band gap of Li[sub x]WO[sub 3] as a function of x were determined. A progression in the crystal structure from monoclinic to cubic for higher values of x was observed for both Li[sub x]WO[sub 3] and Na[sub x]WO[sub 3]. In the cubic regime a lattice contraction and an expansion was observed with x for Li[sub x]WO[sub 3] and Na[sub x]WO[sub 3]. Rf sputter deposited films were polycrystalline and the degree of crystallinity was observed to increase with deposition temperature and sample annealing. The crystal structure of the films was reversible upon insertion and removal of lithium. The optical reflectivity spectrum exhibited a free electron like behavior and increased with increasing x. The optical reflectivity spectrum for the lithiated WO[sub 3] films behaved similarly to that of single crystals. The free electron scattering was higher for the thin films. Films which were annealed showed higher R([lambda]) and lower scattering compared to unannealed films. Crystalline perfection of the films appeared to be a key factor in achieving a high R([lambda]). The electron effective mass and the intrinsic band gap decreased with increasing x in Li[sub x]WO[sub 3]. Highly crystalline lithiated tungsten trioxide thin films are well suited for the working electrode in electrochromic [open quotes]SMART WINDOW[close quotes] devices, and improved crystallinity of these films will result in further improvement of device performance.
- Research Organization:
- Tufts Univ., Medford, MA (United States)
- OSTI ID:
- 7274380
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360102 -- Metals & Alloys-- Structure & Phase Studies
360104* -- Metals & Alloys-- Physical Properties
ALLOYS
COPPER ALLOYS
COPPER BASE ALLOYS
CRYSTAL STRUCTURE
CRYSTALS
ELECTRO-OPTICAL EFFECTS
ELECTROCHROMISM
ELECTROMAGNETIC RADIATION
INFRARED RADIATION
LITHIUM ALLOYS
MONOCRYSTALS
NEAR INFRARED RADIATION
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RADIATIONS
TUNGSTEN ALLOYS
TUNGSTEN BRONZE