Millimeter-wave Dielectric Properties of Titanite-based Ceramics with Nominal Composition CaTi_1-xNb_4x/5SiO₅

抄録

The titanite-based ceramics with nominal composition CaTi_1−xNb_4x/5SiO₅ (0 ≦ x ≦ 0.2) in which part x of Ti sites are occupied with Nb, showed a remarkable jump of the complex relative permittivity at x = 0.025 compared with that at x = 0 at 110 GHz. Real part increased from 22.5 to 39, and the imaginary part from 4 to 14 (tangent delta from 0.18 to 0.36). Non-reflection condition is fulfilled in both cases when 0 < x < 0.0125, d/λ₀ = 0.05 and x = 0.2, d/λ₀ = 0.045, where d is thickness of the plate sample and λ₀ is the wavelength of incident electromagnetic wave. The dominant dielectric dispersion may occurr due to difference of ionic polarization between Ti⁴⁺ and Nb⁵⁺ ions relative to O²⁻ ions, which becomes inactive and saturates at x = 0.025. From the measurement of the lattice parameters, a, b, c, and the angle β, characterizing monoclinic crystal structure, this saturation may have close correlation with some structural rearrangement of constituting atoms, Ti and Nb in CaTi_1−xNb_4x/5SiO₅.