Ba4Nd2Ti4Ta6O30 dielectric ceramics with high-e and low dielectric loss were modified to improve the temperature coefficient of dielectric constant. Through partial substitution of Ti4+ for Ta5+, a significantly reduced temperature coefficient of dielectric constant (te 4 −664p pm/℃) combined with a dielectric constant above 110 and a low dielectric loss (tand-0.0005 to 0.0006 at 1MHz) resulted in the nonstoichiometric dielectric ceramics with nominal compositions Ba4Nd2Ti4+xTa6−xO30−x/2 (x 4 0.8-1.2).

(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.