Abstract
The titanite-based ceramics with nominal composition CaTi1−xNb4x/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 CaTi1−xNb4x/5SiO5.
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