“…Electrorheological (ER) fluids composed of polarizable solid particles dispersed in an insulating medium are suspensions whose viscosity or shear strength can reversibly and quickly change under an applied external electric field. − This phenomenon has attracted much attention from both academic and industrial communities for potential uses in various mechanical devices, such as clutches, valves, and damping devices. − However, until now, there are still several limitations for commercialization of ER fluids because of relatively low polarization force. − To overcome the poor ER effect, many efforts have been made to improve the ER performance, such as doping with rare-earth (RE) ions, − changing the morphology, , and designing complex structure. − Among these efforts, the doping element is a simple and effective method to improve the ER activity. Nevertheless, this method often induces the change of the material composition, crystal structure, intermicrostructure, the size of particles, defects, and charge-carrier state.…”