Crystal structure and microwave dielectric properties of (1 - X)ZnTa ₂O ₆-xTiO ₂ ceramics

The crystal structural variations of (1 - x)ZnTa ₂O ₆-xTiO ₂ ceramics sintered at 1250 °C for 2 h were investigated, and the relationship of these variations with the microwave dielectric properties were studied. Four types of crystal structures were identified with increasing x: tri-α-PbO ₂, α-PbO ₂, trirutile, and rutile. For x ≤ 0.2, single-phase solid solutions of the tri-α-PbO ₂ structure were formed, whereas for x = 0.4, a mixture of two solid solution phases based on the α-PbO ₂ and trirutile structures was obtained. For x = 0.5, a single phase of ZnTiTa ₂O ₈ with the trirutile structure was obtained, and for x ≥ 0.6, the ceramics formed single-phase solid solutions of the rutile structure. The microwave dielectric properties of the ceramics were changed by the crystal structural transitions: for x < 0.4, the phases of the tri-α-PbO ₂ or α-PbO ₂ structures exhibited ZnTa ₂O ₆-like dielectric behavior, while for x ≥ 0.4, the phases of the trirutile or rutile structure exhibited more TiO ₂(rutile)-like behaviors as x increased. The ZnTiTa ₂O ₈ (x = 0.5) ceramics had a dielectric constant (k) of 46.2, a quality factor (Q × f) of 36,700 GHz, and a temperature coefficient of the resonant frequency (τ _f) of +74 ppm/°C.