Crystal structure and microwave dielectric properties of (1 − x)ZnTa2O6–xTiO2 ceramics

The crystal structural variations of (1 − x)ZnTa2O6–xTiO2 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-PbO2, α-PbO2, trirutile, and rutile. For x ⩽ 0.2, single-phase solid solutions of the tri-α-PbO2 structure were formed, whereas for x = 0.4, a mixture of two solid solution phases based on the α-PbO2 and trirutile structures was obtained. For x = 0.5, a single phase of ZnTiTa2O8 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-PbO2 or α-PbO2 structures exhibited ZnTa2O6-like dielectric behavior, while for x ⩾ 0.4, the phases of the trirutile or rutile structure exhibited more TiO2(rutile)-like behaviors as x increased. The ZnTiTa2O8 (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 (τf) of +74 ppm/°C.

► Four types of crystal structures in (1 − x)ZnTa2O6–xTiO2 ceramics.
► Relationship between the crystal structures and microwave dielectric properties.
► Trirutile-structured ZnTiTa2O8 phase.