Composite Dielectric Ceramics Based on BaO–Ln₂O₃–TiO₂ (Ln = Nd, La)

Abstract

BaLa 4 Ti 4 O 15 (BLT) is a hexagonal perovskite-related compound with a temperature coefficient of resonant frequency ( f ) of À2 ppm/ C, relative permittivity ð" r Þ $ 44 and figure of merit ðQ Á f Þ $ 44000 GHz. Ba 4 Nd 9:333 Ti 18 O 54 (BNT) has a tungsten-bronze-related structure with " r $ 78, Q Á f % 11000 GHz and f of þ47 ppm/ C. The microstructures and microwave dielectric properties of xBNT-(1 À x)BLT (0 x 1) composite ceramics have been studied. X-ray diffraction analysis and scanning electron microscopy revealed that there was limited inter-reaction between the two phases and that samples were composed largely of BNT and BLT, although some deterioration in measured " r with respect to calculated values was observed. The optimum compositions were x ¼ 0:55 and 0.75 for which " r $ 63, f $ À20 ppm/ C and Q Á f > 10;000 GHz.

Effect of glass additions on the sintering and microwave properties of composite dielectric ceramics based on BaO–Ln2O3–TiO2 (Ln=Nd, La)

“…For BLT/0.1BBZS ceramics, relative densities ≥95% were achieved at ∼1140 • C, reducing the sintering temperature by 310 • C compared to pure BLT (1450 • C). 1 In comparison with BLT/0.1BBZS and BNT/0.1BBZS, relative densites ≥95% of theoretical for composite ceramics BNLT/0.1BBZS, x = 0.25, 0.55 and 0.75 were achieved by sintering at ∼1140 • C, a reduction of ∼310 • C in sintering temperature. 1 Although a decrease in densification was achieved through the glass addition, the discrepancy in the reduction in sintering temperatures between BLT/0.1BBZS and BNT/01.BBZS suggests that 10 wt% was insufficient to form a interconnected matrix of liquid phase throughout the composite during sintering.…”

“…It is suspected that these two bands may be of the similar nature to the B-site order-disorder bands observed in complex or solid solution perovskites as reported 9-11 due to the La/Nd cations occupying the similar sites; however it is also possible that these two bands arise from second phases present in the intermediate compositions as discussed in previous work. 1 Fig. 12 reveals that the ε r of BNT/0.1BBZS ceramics is ∼71, compared with BNT, ε r = 78.…”

Circularly Polarized Dielectric‐Loaded Antennas: Current Technology and Future Challenges

“…However, there are significant materials problems associated with obtaining suitable temperature stable ceramics with permittivities greater than 50 whose Q values are sufficiently high to ensure that the antenna gain is adequate. [11] The only candidate materials are based on the solid solution, Ba 6À3x RE 8þ2x Ti 18 O 54 (BRET, where RE ¼ La, Nd, Sm, Pr) whose permittivities lie between 75 and 90 and with Q at 1 GHz $ 10,000. [15] The BRET structure diagram is shown in Figure 7.…”

“…Figure 6. Q x frequency (Q f o ) versus relative permittivity (e r ) for modern microwave ceramics for base station filter applications, after Zheng et al [11].…”

“…List of ceramics currently utilized as filters in mobile phone base stations, after Zheng et al[11].…”