Structure and Microwave Dielectric Properties of Hexagonal Ba[Ti1−x(Ni1/2W1/2)x]O3 Ceramics

Microwave dielectric ceramics with the composition of Ba[Ti1−x(Ni1/2W1/2)x]O3 (x=0.4–0.6) were prepared by a solid‐state reaction method. The evolution of the crystalline phases was investigated by X‐ray powder diffraction analysis. A cubic‐to‐hexagonal phase transition occurred between 1000° and 1300°C. The phase transition is irreversible; thus, the hexagonal phase remains stable at room temperature. The X‐ray powder diffraction data for x=0.5 were refined using the Rietveld method. It was identified as a h‐BaTiO3‐type hexagonal perovksite with the space group of P63/mmc. It also reveals that random occupancy of Ti4+ and W6+ ions occurs in the B‐site substructures, whereas Ni2+ ions exclusively occupy the octahedral site in the corner‐sharing octahedron. The dielectric properties of dense‐sintered ceramics were characterized at microwave frequencies. With an increase in x from 0.4 to 0.6, the Q×f value increased from 26 700 to 42 000 GHz, whereas ɛr decreased from 29.8 to 20.0, and τf from +6.5 to −9.9 ppm/°C.