Electronic states and cation distributions of MgAl2O4 and Mg0.4Al2.4O4 microwave dielectric ceramics

摘要

The electronic state and microwave dielectric properties of MgAl2O4 prepared using solid-state (MA-S) and molten salt (MA-M) methods and those of Mg0.4Al2.4O4 (M04A24) were investigated. The lambda values, which correspond to the fraction of Al3+ cations in tetrahedral sites, for MA-S, MA-M, and M04A24 were 0.23, 0.41, and 0.60, respectively. In molecular orbital calculations, a larger overlap was observed between Al-3s or Al-3p in tetrahedral sites and O-2p orbitals for M04A24, and the bond order for Al-O at tetrahedral sites of M04A24 (0.241) was higher than those for MA-S (0.178) and MA-M (0.205). The dielectric constant, epsilon(r), for M04A24 (7.6) was lower than those for MA-S and MA-M (both 7.9), and the highest quality factor, Q.f was obtained for M04A24 (235, 800 GHz). It was found that the covalency of the Al-O bonds in the MO4 tetrahedra is closely related to the Q.f values of the present ceramics.