The dielectric resonator (DR) antennas with probe-feed in both cylindrical and rectangular shape using high permittivity ceramics were investigated. The bismuth-based low-firing ceramics with the ielectric constants of 97, 71 and 37 were adopted as dielectric materials, respectively. The result of theoretical calculation and experimental measurement are presented and analyzed.

The structures, phase transformations, and dielectric properties of pyrochlore ceramics containing bismuth were studied. The relation between the orthorhombic and cubic pyrochlores in the Bi2O3-ZnO-Nb2O5 (BZN) system has been investigated. The effect of bismuth in distorted cubic pyrochlore structures is discussed. BZN compositions with pyrochlore structures have excellent dielectric properties,very low dielectric loss, and high dielectric constants with stable frequency and temperature dependence.

The cubic pyrochlore structure of Bi1. 5Zn1. 0Nb1. 5O7 was investigated. The crystal chemical formula of this material was determined as Bi1. 5Zn0.5 (Zn0.5Nb1.5) O7 by comparing the calculated theoretical X-ray diffraction intensities with the observed ones. Crystal structure parameters were refined by Rietveld method. The (Bi1.5 2yZn1 2yNb1.5) O7 y crystalline samples were also examined by Raman spectroscopy to look for further short range structural information. The results show that the Nb/O and Zn/O tretching modes in the B site oxide octahedral almost do not change with the chemical constitution changing. It is reasonable that the movable Zn2 is inclined to occupy B site first and then enter into A site after the B site was stuffed.

The effects of V2O5 on the phase formation and dielectric properties of Bi2O3-ZnO-Nb2O5 (BZN) pyrochlore ceramics were investigated. With the small amount of V2O5 substitution (0.005≤x≤0.05), the sintering temperatures of Bi1.5Zn0.5 (Zn0.5Nb1.5−xVx) O7 can be effectively reduced from 1000 to 840◦C while the phase structures still kept to be the pure cubic pyrochlores. The V2O5 seems to provide an eutectic melt below the sintering temperature to improve the sinterability. The dielectric constants decrease gradually with V2O5 substitution while the temperature coefficients of the samples continuously increase. The dielectric loss are in same level as that of the basic composition at the smaller substitute amount (x≤0.02) but then degraded in lower frequency when the substitution reached to x = 0.05. Obvious dispersion in the dielectric constant and loss was observed as a function of frequency and temperature after the substitution.

The preparation, microstructure development and dielectric properties of Bi1.5ZnNb1.5O7 pyrochlore ceramics by metalloorganic decomposition (MOD) route are reported. Homogeneous precalcined ceramic powders of 13-36nm crystallite size were obtained at temperatures ranging from 500 to 700 8C. The thermal decomposition/oxidation of the gelled precursor solution was chemically analyzed, TG/DTA, XRD, and SEM, led to the formation of a pure cubic pyrochlore phase with a stoichiometry close to Bi1.5ZnNb1.5O7 which begins to form at 500 8C. The metallo-organic precursor synthesis method, where Bi, Zn and Nb ions are chelated to form metal complexes, allows the control of Bi/Zn/Nb stoichiometric ratio on a molecular scale leading to the rapid formation of bismuth zinc niobate (Bi1.5ZnNb1.5O7) ceramic fine powders with pure pyrochlore structure. The powders were pressed into pellets and can be sintered at temperatures as low as 800-1000 8C. Fine crystalline ceramics with the grain size in the range of 200-500 nm have been obtained at the sintering temperature of 800 8C. The dielectric properties in high frequency to microwave range were measured and discussed.

The effect of La2O3 substitutions on structure and dielectric properties of Bi2O3-ZnO-Nb2O5-based ceramics was investigated. Bi1.52xLaxZn0.5 (Zn0.5Nb1.5) O7 samples were prepared by conventional ceramic processing technology. The crystal structure of the Bi1.5Zn0.5 (Zn0.5Nb1.5) O7 sample was characterized as a pure cubic pyrochlore. With a lower amount of La2O3 substitution, the crystal structures were still cubic pyrochlore. Superlattice x-ray diffraction line was identified for some compositions. With the increasing amount of La2O3 substitution, the crystal structure gradually transformed from pure cubic pyrochlore to LaNbO4 phase. The dielectric properties regularly changed with the structure change. The structure-properties relations of the ceramics are discussed.

The structure and dielectric properties of Bi2O3-ZnO-Nb2O5-based ceramics with pyrochlore-fluorite biphase structure were investigated. Mixed-sintered ceramics were prepared by two precalcined constituents in the system of x [Bi1.5Zn0.5 (Zn0.5Nb1.5)O7]-(1-x)Bi3/4Nb1/4O7/4 (0.05x0.35), where Bi1.5Zn0.5 (Zn0.5Nb1.5) O7 is a cubic pyrochlore (a) and Bi3/4Nb1/4O7/4 is a defect cubic fluorite (F). The phase composition of the mixed-sintered ceramics were characterized as a biphasic structure with a distorted pyrochlore (b) and a fluorite (F) coexisting. The phase ratio of b pyrochlore and F fluorite is related to the chemical composition x. The dielectric properties of the ceramics gradually change with their structure.

The ion substitution with Mn4+ and W6+ co-substituted Nb5+ in B site of a low firing Bi2O3-ZnO-Nb2O5-based A2B2O7 pyrochlore ceramicswas investigated. TheMn4+ andW6+ co-substitutionwas tentatively introduced in cubic-monoclinic pyrochlores co-existing ceramics Bi3xZn2−3x (ZnxNb2−x−2yMnyWy) O7 (x = 0.5-0.65, y=0, 0.02, 0.05, 0.1) and the results shows interested regular influence on the structure, dielectric properties with the amount of substitution amount change. With the structure evaluation and electrical properties measurement results, the Mn4+ and W6+ substituted Nb5+ in B site shows effective to depress the grain growth and the ceramic with fine grains in 1-3m can be obtained. The electrical properties was also enhanced in smaller substitution amount but degraded with the substitution amount increasing. Based on these results, small amount of Mn4+ andW6+ substitution was successfully applied to a base ceramic with the electrical properties satisfied the NP0 specification to miniaturize the grains and enhance the sintering behavior.