Changes of the Electro-optic Response of Nematic Liquid Crystal Cells Due to inserted Titania-Vanadia Films

We report a polarity-sensitive electro-optical response observed in nematic liquid crystal cells characterized by asymmetric insertion of thin films of titania-vanadia oxide with a Ti/V atomic ratio of 1/1, prepared by sol-gel synthesis on transparent indium tin oxide. The electro-optical effect is opposite to previously reported ones but is obtained using the same materials with a slightly different sol-gel route. The structural properties of titania-vanadia films are extensively studied with particular attention paid to the thermal history of the films. The measurements made of the films and on the nematic liquid crystal cell demonstrate that the crystalline structure of the film is responsible of the observed effect. Thermal annealing of the films results in formation of structures that dramatically change the electric properties of the films. A qualitative model is proposed to explain the surface charge distribution inside the nematic liquid crystal cell that results in the observed electro-optical effect.