Highly Improved Dielectric Properties of Polymer/α-Fe2o3 Composites at Elevated Temperatures

alpha-Fe2O3 particles were incorporated into ten kinds of polymer matrices, and the dielectric properties of the resultant polymer/alpha-Fe2O3 composites were investigated between 40 degrees C and 160 degrees C. We found that the dielectric properties strongly depended not only on the temperatures but also on the kind of polymer matrices. For engineering plastics such as polyetherimide (PEI), the dielectric constant epsilon '(r) was highly enhanced at around 1 kHz by incorporation of the alpha-Fe2O3 particles owing to Maxwell-Wagner polarization of free electrons in the alpha-Fe2O3 particles. This is probably because the pi electrons in the aromatic structures of the engineering plastics strongly interact with the electrons in the alpha-Fe2O3 particles. Furthermore, the dielectric loss factor epsilon ''(r) for the engineering plastics became small at elevated temperatures because the conductivity of the alpha-Fe2O3 particle was enhanced and therefore the relaxation frequency of Maxwell-Wagner polarization was shifted to higher frequency. PEI/alpha-Fe2O3 composites exhibited highly improved dielectric properties at around 1 kHz, the high epsilon '(r) and very low epsilon ''(r) at the elevated temperatures above 120 degrees C. It was demonstrated that the PEI/ alpha-Fe2O3 composite was comparable to the PEI/BaTiO3 composite in dielectric performance at 160 degrees C. Because the cost of alpha-Fe2O3 is much lower than that of BaTiO3, the PEI/alpha-Fe2O3 composite might be promising as a low-cost dielectric material for high-temperature applications.