3 mol% yttria stabilized tetragonal zirconia caramics (3Y-TZP) were significantly toughened by a Sr2Nb2O7 ferroelectric secondary phase incorporated into the matrix to serve as toughening agent. A high KIC value, 13.0MPa. M1/2 was achieved in 1mol% Sr2Nb2O7 composite ceramics, while that of the 3Y-TZP matrix was 6.0MP a. m1/2. Energy transformation and consumption due to piexoelectric effects and domain wall motion was suggested as an important toughening mechanism along with that fo phase transformation toughening. Moreover, it should be emphasized that a high KIC value of 12.0MPa. m1/2 was achieved in the present composite ceramics even where the transformation toughening mechanism was inactive.

The effects of Bi substitution for Nd in Ba6−3xNd8+2xTi18O54 (x 4 2⁄3) solid solution upon the microstructures and microwave dielectric properties were investigated. The solid solubility limit of Bi in Ba6−3xNd8+2xTi18O54 (x 4 2⁄3) solid solution was about 15mol%, the same as that for x 4 0.5, and densification of the present solid solutions could be performed well at lower temperatures. However, the variation tendency of microwave dielectric properties with composition in the present ceramics quite differed from that for x 4 0.5: (1) The temperature coefficient of resonant frequency in the present ceramics showed a continuous variation from positive to negative and did not indicate extreme value at the solid solubility limit. (2) Near-zero temperature coefficient of resonant frequency combined with high-e and high-Qf values could be obtained in the present ceramics, while that for x 4 0.5 had a lower limit of +15 ppm/℃. (3) The dielectric constant also showed a continuous increase for the present compositions, while that in x 4 0.5 had an extreme at solid solubility limit. Ceramics with composition of Ba6−3x(Nd0.85,Bi0.15)8+2xTi18O54 (x 42⁄3) showed excellent dielectric properties of e 4 99.1, Qf4 5290 GHz, and tf4 −5.5 ppm/℃.

BaTi4O9 and Ba2Ti9O20 precursors were prepared via a sol- gel method, using ethylenedi aminetetra acetic acid as a chelating agent. The sol-gel precursors were heated at 700℃-1200℃ in air, and X-ray diffractometry (XRD) was used to determine the phase transformations as a function of temperature. Single-phase BaTi4O9 could not be obtained, even after heating the precursors at 1200℃ for 2h, whereas single-phase Ba2Ti9O20 (as determined via XRD) was obtained at 1200℃ for 2h. Details of the synthesis and characterization of the resultant products have been given.

Ba623xNd812xTi18O54 ceramic powders were synthesized by the modified Pechini method using ethylenediaminetetraacetic acid (EDTA) as a chelating agent. A purplish red, molecularlevel, homogeneously mixed gel was prepared, and transferred into a porous resin intermediate through charring. Singlephase and well-crystallized Ba623xNd812xTi18O54 powders were obtained from pulverized resin at a temperature of 900

Modification of the microwave dielectric properties in Ba6-3xNd8+2xTi18O54 (x=0.5) solid solutions by Bi/Sm cosubstitution for Nd was investigated. A large increase in the dielectric constant and near-zero temperature coefficient combined with high Qf values were obtained in modified Ba6-3xNd8+2xTi18O54 solid solutions where an enlarged solid solution limit of Bi in Ba6-3xNd8+2xTi18O54 was observed. Excellent microwave dielectric characteristics (e=105, Qf=4110 GHz, and very low tf) were achieved in the composition Ba6-3x(Nd0.7Bi0.18Sm0.12)8+2xTi18O54.