TY - JOUR

T1 - Phase transformation of lithium tungsten bronzes, LixWO3, at room temperature ambient conditions

AU - Dey, K. R.

AU - Rüscher, C. H.

AU - Gesing, Th M.

AU - Hussain, A.

N1 - Funding Information: This work has been supported by the “Alexander von Humboldt Stiftung” under collaborative research program (V-FOKOOP/DEU/1062067/Hussain) and by German Science foundation (DFG, RU764/1–2). K. R. Dey is grateful for the “Lichtenberg Stipendium” of the “Land Niedersachsen” to pursue her studies at Hannover University for her Ph.D. degree. The authors are thankful for useful comments and advise of an unknown referee.

PY - 2007/4/12

Y1 - 2007/4/12

N2 - Samples of LixWO3 with x = 0.05-0.7 were synthesized at 700 °C for 7 days using appropriate amounts of Li2WO4, WO3 and WO2 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-1 in the Kubelka Munk spectra which is related to the cubic LixWO3 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 LixWO3. X-ray and IR data show a gradual transformation into the lower symmetric phases (PTBcubic ⇒ PTBtetragonal ⇒ PTBorthorhombic ⇒ PTBmonoclinic). The results suggest that Li is attracted by O2 to the surface forming Li2O which further reacts with H2O and CO2 in air. The in air altered samples regain their original colour when reheated at 500 °C in vacuum.

AB - Samples of LixWO3 with x = 0.05-0.7 were synthesized at 700 °C for 7 days using appropriate amounts of Li2WO4, WO3 and WO2 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-1 in the Kubelka Munk spectra which is related to the cubic LixWO3 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 LixWO3. X-ray and IR data show a gradual transformation into the lower symmetric phases (PTBcubic ⇒ PTBtetragonal ⇒ PTBorthorhombic ⇒ PTBmonoclinic). The results suggest that Li is attracted by O2 to the surface forming Li2O which further reacts with H2O and CO2 in air. The in air altered samples regain their original colour when reheated at 500 °C in vacuum.

KW - A. Inorganic compounds

KW - B. Crystal growth

KW - C. Infrared spectroscopy

KW - C. X-ray diffraction

KW - D. Optical properties

UR - http://www.scopus.com/inward/record.url?scp=33847237568&partnerID=8YFLogxK

U2 - 10.1016/j.materresbull.2006.08.025

DO - 10.1016/j.materresbull.2006.08.025

M3 - Article

AN - SCOPUS:33847237568

VL - 42

SP - 591

EP - 599

JO - Materials research bulletin

JF - Materials research bulletin

SN - 0025-5408

IS - 4

ER -