Chi Yuen Huang

Structure and Microwave Dielectric Property Relations in Barium Cobalt Magnesium Niobate Ceramics

The effects of cobalt substitution for magnesium on the microstructure and microwave dielectric properties of Ba(Mg1/3Nb2/3)O3 are investigated using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), Raman spectra, and microwave dielectric properties measurement. The structure of NbO6 octahedra displays a significant effect on the relative dielectric constant (er) and the quality factor (Q ×f). The cobalt substitution shows a great quantity of nucleation of ordered domains, and result in a higher ordering degree. However, an annealing treatment also results in a higher ordering degree because of the growth of ordered domains. A compounds with near-zero τf can be obtained by the cobalt substitution. The Ba(Mg1-xCox)1/3Nb2/3O3 ceramic with cobalt substitution at x = 0.5 has the 32.2 of er, 40,275 GHz of Q ×f, and 5.4 ppm/°C of τf, and it is suitable for microwave resonator application. This study indicates that the cobalt substitution cause a variant of the ordering degree, and consequently has a significant effect on the microwave dielectric properties.

Microwave dielectric properties of (Ba1-xMgx) 5Nb4O15 ceramics

The effects of magnesium substitution for barium on the microstructure and microwave dielectric properties of Ba5Nb4O15 are investigated using X-ray diffractometry, scanning electron microscopy, Raman spectroscopy, and microwave dielectric properties measurement. The structure of NbO6 octahedra and the ionic polarizability have a significant effect on the relative permittivity (er). Furthermore, a distinct correlation is noted between the secondary phases and microwave dielectric properties. The magnesium substitution at x=0.6 for (Ba1-xMgx)5Nb4O15 formulation has the 27.6 of er, 13,985 GHz of Q×f, and 2.5 ppm/°C of τf, and it is suitable for microwave resonator application.

Phase Evolution and Nucleus Growth Observation of Solid-State BaTiO3 Powder Prepared by High-Energy Bead Milling for Raw Material Mixing

The solid-state synthesis, phase evolution, and nucleus growth of the barium titanate (BaTiO3, BT) powder were investigated in this study. Rapid nucleus growth and precursor phase formation of BT were observed at a relatively low temperature of 600 °C by mixing BaCO3 (2 m2/g) and TiO2 (7 m2/g) with a high-energy bead mill. The decomposition of BaCO3 and the formation of the Ba2TiO4 phase were identified by transmission electron microscopy (TEM). On the basis of this observation, the weight loss observed at 600 °C in the derivative thermogravimetry (DTG) curve could also be explained. Furthermore, with increasing calcination temperature, single cubic BT with less than 80 nm fine nuclei/crystallites was observed at 900 °C, and tetragonal BT (c/a > 1.008) with an average particle size of 0.4 µm was obtained at 1000 °C. With regard to the dielectric properties of sintered ceramics, the relative permittivity (er) increased with calcination temperature, and the Curie point also shifted to a progressively higher temperature. However, BT nucleus samples (with low calcination temperatures of 800 and 900 °C) could not satisfy the X7R requirement (Electric Industries Association Standard, the tolerance of capacitance from -55 to +125 °C is ±15%) until calcination temperature increased to 1000 °C.

Structural and Dielectric Characteristics of Calcium Strontium Magnesium Niobate

The dielectric and structural characteristics of (Ca1-xSrx)(Mg1/3Nb2/3)O3, (x = 0–0.5) solid solutions are investigated by measuring and observing these properties by X-ray diffractometry, transmission electron microscopy, and Raman spectroscopy. The splitting of superlattice reflections shows that the (Ca1-xSrx)(Mg1/3Nb2/3)O3 solid solution has a 1:2 ordered structure distorted by the antiphase, the in-phase tilting of oxygen octahedra, and the antiparallel shift of cations at 0 ≤x ≤0.5. The strontium substitution causes a tolerance factor increase, which leads to higher structure symmetry. This study indicates that ionic polarizability, tolerance factor, cation substitution, and grain size have a significant effect on the microwave dielectric properties of this solid solution.