Phase transformation of lithium tungsten bronzes, Li {sub x}WO{sub 3}, at room temperature ambient conditions
- Institute for Mineralogy and ZFM, Hannover University, Welfengarten 1, D-30167 Hannover (Germany)
- Department of Chemistry, University of Dhaka, Dhaka 1000 (Bangladesh)
Samples of Li {sub x}WO{sub 3} with x = 0.05-0.7 were synthesized at 700 deg. C for 7 days using appropriate amounts of Li{sub 2}WO{sub 4}, WO{sub 3} and WO{sub 2} in evacuated sealed silica tubes. The products reveal different phases of perovskite tungsten bronze (PTB). An interesting phenomenon observed for the PTB phases is the gradual change in colours when they are exposed at room temperature ambient conditions (in air). This effect has been investigated using X-ray powder diffraction, infrared absorption and optical reflectivity methods for the powdered samples before and after 30 and 90 days in air. The spectra of the samples with x = 0.25-0.5 are dominated by a peak with maximum around 16,000 cm{sup -1} in the Kubelka Munk spectra which is related to the cubic Li {sub x}WO{sub 3} phase. The peak intensity increases with increasing x. After 30 days of exposure in air this peak disappeared for x < 0.5 samples due to a diffusion of Li from Li {sub x}WO{sub 3}. X-ray and IR data show a gradual transformation into the lower symmetric phases (PTB{sub cubic} {sup {yields}} PTB{sub tetragonal} {sup {yields}} PTB{sub orthorhombic} {sup {yields}} PTB{sub monoclinic}). The results suggest that Li is attracted by O{sub 2} to the surface forming Li{sub 2}O which further reacts with H{sub 2}O and CO{sub 2} in air. The in air altered samples regain their original colour when reheated at 500 deg. C in vacuum.
- OSTI ID:
- 21000612
- Journal Information:
- Materials Research Bulletin, Vol. 42, Issue 4; Other Information: DOI: 10.1016/j.materresbull.2006.08.025; PII: S0025-5408(06)00353-9; Copyright (c) 2006 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0025-5408
- Country of Publication:
- United States
- Language:
- English
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