(1-x)Pb(Mg1/3Nb2/3)O3-xLa(Mg1/2Ti1/2)O3 dielectrics were prepared by a solid-state reaction process and the structures were evaluated together with the dielectric characterization. The pyrochlore-free dielectrics were obtained with increasing La(Mg1/2Ti1/2)O3 content due to the increased electrone gativity difference. The 1/2 (111) superlattice reflection showed 1:1 ordering on the B site in all compositions. Antiphase tilting of oxygen octahedra and B-site cation displacing appeared at x50.9. Low loss (tand; 1024) dielectrics with high dielectric constant (36-900) Were obtained in the present system, and the good microwave dielectric properties were achieved in the compositions with x>0.7. The best combination of microwave dielectric properties was obtained for x50.9: e534, Qf521 280GHz, and t f5260 ppm/℃.

Dielectric ceramics were synthesized and characterized in the BaO-La2O3-TiO2-Ta2O5 quaternary system for the three typical compositions: Ba3La3Ti5Ta5O30, Ba4La2Ti4Ta6O30 and Ba5LaTi3Ta7O30, which formed the filled tungsten-bronze structures. The present ceramics indicated high dielectric constant (127.7-148.1) and low dielectric loss tand (in the order of 10-4-10-3 at 1MHz). Meanwhile, the temperature coefficient of dielectric constant varied from -728 to -1347 ppm/C with increasing Ba and Ta and decreasing La and Ti concentration in the temperature range of 20-85 C. The present ceramics are promising candidates for high-and low loss dielectric ceramics, and the suppression of should be the primary issue in the future work.

SrLnAlO4 (Ln Nd and Sm) ceramics with K2NiF4 structure were prepared by a solid state reaction approach, and their microwave dielectric characteristics were evaluated together with the microstructures. The single phase dense SrNdAlO4 and SrSmAlO4 ceramics were obtained by sintering at 1450-1475℃ and 1475-1500℃, respectively, and the good microwave dielectric characteristics were achieved: (1) ε = 17.8, Q · f = 25,700GHz, τ f = −9ppm/℃ for SrNdAlO4; and (2) ε = 18.8, Q · f = 54,880GHz, τ f = 2ppm/℃ for SrSmAlO4 dense ceramics. The Q f value significantly increased with increasing sintering temperature.

Tin (Sn) substitution into the B-site and Nd/Sn cosubstitution into the A- and B-sites were investigated in a Ba6-3xSm8+2xTi18O54 solid solution (x=2⁄3). A small amount of tin substitution for titanium improved the temperature coefficient of resonant frequency (f) but led to a decrease of the relative dielectric constant (з) and the quality factor (Qf). The Ba6-3xSm8+2x(Ti1-zSnz)18O54-based tungsten-bronze phase became unstable for compositions with a tin content of >10mol%, where BaSm2O4 and Sm2(Sn,Ti)2O7 appeared, and finally, these phases became the major phases. On the other hand, Nd/Sn cosubstitution led to a good combination of high ε, high Qf, and near-zero Tf. Excellent microwave dielectric properties were achieved in Ba6-3x(Sm1-yNdy)8+2x(Ti1-zSnz)18O54 ceramics with y=0.8 and z =0.05 sintered at 1360℃ for 3h:=82, Qf=10 000GHz, and calculated Tf=+17 ppm/℃. The tolerance factor and electronegativity difference exhibited important effects on the microwave dielectric properties, especially the Qf value. A large tolerance factor and high electronegativity difference generally led to a higher Qf value.

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.