Search

The dielectric and ferroelectric characteristics of ( Sr x Ba1− x) Nb2 O6 unfilled tungsten bronze ceramics have been investigated together with the structure. The dielectric and ferroelectric characteristics of the present ceramics vary significantly with x, and the A1/A2-sites occupancy has been determined as the primary parameter governing this variation tendency. Ba ions tend to occupy A2-sites, Sr ions tend to occupy A1-sites, and one A1-site is empty. When the ratio of Sr/ Ba is close to 1:4 (where four A2-sites are just occupied by Ba ions, and one A1-site is occupied by Sr ion while another A1-site is empty), the normal ferroelectric transition is observed with one anomaly in the tanδ- T curve ( x = 0.25). When the ratio of Sr/ Ba is far away from 1:4, the typical relaxor behavior is indicated together with three anomalies in the tanδ- T curve ( x = 0.75). The incommensurate oxygen octahedral tilting and A-site random distribution are considered to be the structure origins for the relaxor ferroelectricity and low temperature dielectric relaxations. [ABSTRACT FROM AUTHOR]

Dense (1− x)Ca(Mg1/3Ta2/3)O3/ xCaTiO3 ceramics (0.1≤ x≤0.9) were prepared by a solid-state reaction process. The crystal structures and microstructures were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Single-phase solid solutions were obtained in the entire composition range. Long-range 1:2 ordering of B-site cations and oxygen octahedra tilting lead to the monoclinic symmetry with space group P21/ c for x=0.1. For x above 0.1, the long-range ordering was destroyed and the crystal structure became the orthorhombic with space group Pbnm. The microwave dielectric properties showed a strong dependence on the composition and microstructure. The dielectric constant and temperature coefficient of resonant frequency increased nonlinearly as the CaTiO3 content increased while the Qf values decreased approximately linearly. Good combination of microwave dielectric properties was obtained at x=0.45, where ℇr=45.1, Qf=34 800 GHz, and τf=17.4 ppm/°C. [ABSTRACT FROM AUTHOR]

Ca(Zn⅓Nb⅔)O3 microwave dielectric ceramics were prepared using a solid-state reaction process, and their microwave dielectric properties were evaluated as functions of sintering and postdensification annealing conditions. The relationship between microwave dielectric properties and processing was interpreted through the variation of microstructures. The dielectric constant showed slight variation with sintering and annealing conditions, but the Q × f value increased at first and then decreased with Increased sintering temperature, and annealing in oxygen indicated significant improvement in Q × f, especially for the specimens sintered at higher temperatures. The good microwave dielectric properties were obtained in the ceramics sintered at 1225°C in air for 3 h and annealed at 1100°C in oxygen for 8 h: ∊ = 34.1, Q × f = 15 890 GHz, τr = -48 ppm/°C. [ABSTRACT FROM AUTHOR]