Evaluation of relative permittivity and coefficient of thermal expansion of TiO<inf>2</inf>/SiO<inf>2</inf> epoxy composites for permittivity-graded insulator

Abstract

We have been investigating the feasibility of permittivity graded material whose coefficient of thermal expansion (CTE) was low. We have already reported that relative permittivity of TiO 2 /SiO 2 epoxy composites was able to be changed in 3.5–7.5 with keeping CTE low in 23–29 ppm/K by changing the filling ratio of TiO 2 and SiO 2 in keeping the total volume fraction at 50 vol%. In this paper, we evaluated relative permittivity and CTE of the TiO 2 /SiO 2 epoxy composites with using conventional calculation models. The tendency of relative permittivity of the TiO 2 /SiO 2 epoxy composites was roughly explained by Lichitenecker & Rother equation. CTE of the TiO 2 /SiO 2 epoxy composites was in the range between upper and lower limit of a calculation model based on Schapery equation. Furthermore, the range from 3.5 to 7.5 in relative permittivity of the TiO 2 /SiO 2 epoxy composites with low CTE was met the condition necessary for realizing permittivity graded material. The electric field relaxation effect of the permittivity graded material was estimated.