Preparation and Enhanced Electrorheological Activity of TiO₂ Doped with Chromium Ion

TiO 2 is very important electrorheological (ER) material due to its high dielectric constant. But its weak ER activity is amazing. We report here a novel approach to enhance the electrorheological activity of TiO 2 by doping it with chromium (Cr) ion. X-ray diffraction shows that the material possesses the anatase phase when the Cr/Ti molar ratio is smaller than 10%, while phase separation appears upon further increasing the Cr/Ti molar ratio. X-ray photoelectron spectroscopy shows that Cr 6+ and Cr 3+ are codoped in TiO 2 crystal and induce a shift of the binding energy of TiO 2 . Rheological experiments show that Cr-doping significantly enhances the ER activity of TiO 2 . The yield stress τ E of a typical 10 mol % Cr-doped TiO 2 suspension is about 2.3 and 7.0 kPa at 4 kV/mm when the volume fraction is 18% and 34%, respectively. The ER efficiency ((τ E − τ 0 )/τ 0 ) of a typical Cr-doped TiO 2 suspension is about 280 (10.55 s - 1 ) at 3 kV/mm, which is 18 times higher that of pure TiO 2 suspension. Especially, the yield stress shows a marked dependence on Cr doping degree, and ER activity tends to decline with phase separation when the doping degree is higher than 10 mol %. On the basis of the structure analysis and dielectric and conduction measurements, we attribute the enhancement of ER activity of TiO 2 to the improvement in the dielectric and conduction properties, induced by the activated internal structure, including defect and impurities of TiO 2 due to doping with different valent Cr ions.