Crystal structures and microwave dielectric properties of Zn,W co-substituted BaTiO3 perovskite ceramics

Zn,W co-substituted BaTiO3 perovskite ceramics with compositions of Ba[Ti1−x(Zn1/2W1/2)x]O3 (x=0.40–1.00) were synthesized by the conventional solid-state reaction method and studied by X-ray diffraction and dielectric measurements. Their structures transferred from cubic (x=0.40) with space group Pm3¯m to hexagonal (x=0.55–0.60) with P63/mmc, and then to cubic double pervoskite (x=1.00) with Fm3¯m. The refinement results of sample (x=0.60) revealed that the negative and positive charge centers are not consistent with each other in the face-sharing oxygen octahedra. Compared with the cubic perovskites, the hexagonal ones had the increased quality factor (Q×f), the decreased dielectric constant (εr), and especially the near-zero temperature coefficient of resonant frequency (τf), whose absolute values were less than 5 ppm/°C. The relationships between structures and properties were discussed. - Graphical abstract: The departure of the negative and positive charge centers in the face-sharing oxygen octahedra of hexagonal unit cell. Highlights: ► A phase transition from simple cubic to hexagonal and then to cubic double pervoskite occurred. ► Refinement results prove that spontaneous dipoles present in face-sharing oxygen octahedra. ► Hexagonal perovskites had higher Q×f, nearer-zero τf, and lower εr than the cubic ones. ► On the presence of the hexagonal perovskite, |τf| was less than 5 ppm/°C.