Crystal structure and microwave dielectric properties of Ni substituted cordierite ceramics

Department of Materials Science and Engineering, Nagoya Institute of Technology* Materials Research & Development Div. General R & D Laboratories. Taiyo Yuden Co., Ltd., Japan**
â—‹Mio Terada* Keizou Kawamura** Isao Kagomiya* Ken-ichi Kakimoto* Hitoshi Ohsato*

Cordierite (Mg2Al4Si5O18) is characterized by a lower dielectric constant (εr) and lower temperature coefficient of resonance frequency (τf) among the systems of MgO-Al2O3-SiO2. εr of cordierite ceramics prepared by standard solid state reaction method showed 6.19 and its τf exhibited -24 ppm/oC, which was more close to zero compared to other isotropic silicates. However, quality factor (Qf ) value is relatively lower compared to more isotropic silicate such as forsterite, diopside, etc. This study investigated an effect of Ni substitution to improve the Qf value. In addition, we discuss relationship between the crystal structure of the Ni substituted cordierite and microwave dielectric properties, particularly Qf from the viewpoint of crystal structure refined by Rietveld analysis. (Mg1-xNix)2Al4Si5O18 with no secondly phase was obtained in the compositions range of x = 0 - 0.1. Furthermore substitution of Ni caused presence of the secondary phase. εr of (Mg1-xNix)2Al4Si5O18 solid solution slightly increased with increasing the composition x. The τf were almost comparable in the range from x = 0.05 to 0.2. On the other hand, the τf abruptly shifted toward negative value with increasing x from 0.3 to 0.5. The Qf value increased with substituting a small amount of Ni and the highest Qf value of 99,110 GHz was obtained at the composition x = 0.1. According to Rietveld analysis, hexagonal rings composed of corner sharing (Si,Al)O4 tetrahedron in the (Mg0.9Ni0.1)2Al4Si5O18 are more isotropic than that of the Mg2Al4Si5O18, suggesting that the Qf value is improved with the slight variation of the hexagonal rings.