Characterizations Of Mixed Bi/V Oxide Films, Deposited Via Sol-Gel Route, Used As Electrodes In Asymmetric Liquid Crystal Cells

In the search of new materials for electrodes in electrochromic devices and in asymmetric liquid crystal cells, some modifiedvanadium oxide thin films has been investigated. The new gels have been generated by the addition of 10% of bismuth (atomicratio) to the precursors mixture. The sol–gel route started from metal alkoxides, vanadium oxo iso-propoxide and BiCl3dissolved in ethanol (99%), to give the atomic ratio Bi/V = 1:10.The crystallization temperature of such bulk gels has been found by DTA analysis to occur at 320 jC, while only seeds of acrystal phase are found after annealing the dip-coated films at 400 jC, identified as Bi4V6O21 (PDF card no. 33-222).Microscopic visual investigation and micro-Raman analysis were performed on the deposited films, ‘‘as grown’’ and ‘‘400 jCannealed’’. Finally, the films have been tested as electrodes in asymmetric nematic liquid crystal (NLC) cells, to investigate therectification effect. The electro-optic measurements were performed in modified nematic liquid crystal cells for both ‘‘asdeposited’’and annealed films. The voltage dependence of the electro-optical response and the current flow have been analyzedat the same time in the voltage range 10/ + 10 V. A model based on the electrical interaction between both the indium tin oxide(ITO)-Bi/V oxide films and Bi/V oxide films–liquid crystal interfaces is proposed, to explain the electric and electro-opticasymmetric responses of the cells.