Microwave dielectric properties of Ba[Ti0.4Ga0.3Nb0.3(1−x)Sb0.3x]O3 perovskite ceramics

The perovskite Ba[Ti0.4Ga0.3Nb0.3(1−x)Sb0.3x]O3 (x = 0–1.00) solid solutions were synthesized by the conventional solid-state reaction method. The structures and microwave dielectric properties were investigated by X-ray and dielectric measurements. Their crystal structures transferred from the cubic to hexagonal one with increasing x. The oxygen octahedra distortions were described from the refinement data. It revealed that the negative and positive charge centers coincided at the origin in the corner-sharing octahedra, but they did not coincide with each other in the face-sharing ones. Two pairs of dipoles canceled in the face-sharing oxygen octahedra, which had an effect on lowering the dielectric constant (ɛr). The temperature coefficient of resonant frequency (τf) of ceramic at x = 0.50 was −1.1 ppm/°C. The hexagonal perovskite had much higher quality factor (Q × f), nearer-zero τf, and lower ɛr than the cubic one. This was ascribed to the canceled dipoles and more shared oxygen ions in the face-sharing oxygen octahedra.

Dipoles produced by the departure of the negative and positive charge centers in two adjacent face-sharing oxygen octahedra of the hexagonal perovskite.Figure optionsDownload as PowerPoint slideHighlights
► A phase transition from the cubic to hexagonal one was detected.
► Hexagonal perovskite had lower ɛr, higher Q × f and nearer-zero τf than cubic one.
► Oxygen octahedra distortions were described from structure refinement results.
► Not coinciding charge centers produced a dipole in the face-sharing octahedra.
► Canceled dipoles had a reducing effect on ɛr in the hexagonal unit cell.