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Regarding advanced 5G mobile communication, microwave dielectric ceramics are considered as the most potential materials to develop new-generation base station resonators. Herein, ZnNb 2 O 6 ceramics with ε r of approximately 24 have been prepared using the solid-state reaction method, with tailored extra ZnO of x mol% (x = 1, 2 and 3). We have for the first time applied the P-V-L chemical bond theory to investigate ZnNb 2 O 6 ceramics with ZnO doping, by exploring the relationship of dielectric properties and chemical bond characteristics. Particularly, the Raman spectra demonstrates that the full width at half maximum of υ 1 (A g) vibration mode can exhibit significant correlation with the quality factor (Q × f). To further support the experimental study, we have also conducted the first-principle calculation of electron density difference via CASTEP package, which further confirms the change of temperature coefficient of resonance frequency (τ f). Our newly designed ZnNb 2 O 6 ceramics doped with 1 mol% ZnO exhibit excellent dielectric properties, i.e., ε r = 23.74, Q × f = 102,824 GHz and τ f = −55.38 ppm/°C, which demonstrates great potential to construct miniaturized 5G base station with advanced ceramic dielectrics. [ABSTRACT FROM AUTHOR]

The influence of BaO content (up to 15 mol%) on the crystallization behaviour, structure, thermal properties and microwave dielectric properties of the BaO-CaO-B 2 O 3 -SiO 2 glasses and glass-ceramics system was investigated. The glasses were produced by melting at 1400 °C and quenching into water, and the glass-ceramics were produced via heat treatment at temperatures between 750 and 800 °C. The results of X-ray diffraction analysis showed that increasing the BaO content raised the resistance of the glass against crystallization and favoured the transformation of β-CaSiO 3 and α-CaSiO 3 phases, which crystallized in the Ba-free and in low BaO content compositions, into SiO 2 and Ba 4 Si 6 O 16 , which crystallized in compositions with higher concentrations of BaO. The BaO content had little influence on the glass transition temperature ( T g ) and the linear coefficient of thermal expansion (CTE), but strongly reduced the softening point ( T s ). Even the addition of BaO as minor additives resulted in a dramatic reduction of the T s ; for example, the T s decreased from 902 °C for the Ba-free composition to 682 °C for the BaO-containing one (5%). Low values of the dielectric constant (5.9 ≤  ε r ≤ 6.63) and dielectric loss (1.12 × 10 −3 ≤ tan δ  ≤ 3.15 × 10 −3 ) were measured. [ABSTRACT FROM AUTHOR]

Temperature stable microwave dielectric materials xBaTiO-(1 − x)BaSmTiO were produced through a conventional solid-state reaction procedure in the work. The structural and microwave dielectric properties of the ceramics were determined with the purpose of finding a microwave ceramics with high dielectric constant (ε), high quality factor (Q × f) and zero temperature coefficient of resonant frequency (τ). Experimental results showed that BaTiO additions affected grain growth and densification, the grain size distribution, and tuned the dielectric properties of the produced ceramics. The amount of BaTiO strongly influenced the densification and the microstructure (i.e. grain shape and size) of the produced ceramics. Analysis of the experimental results suggests that the microstructural features can be correlated to the dielectric properties of these ceramics. Accordingly, the dielectric constant (ε) and the temperature coefficient of resonant frequency (τ) of the produced BaSmTiO ceramics can be tuned with the amount of BaTiO additions and the sintering process parameters. The best dielectric properties were achieved for BaSmTiO ceramics with 15% BaTiO (ε = 66, Q×f = 15,730 GHz and τ ≈ 0 ppm/°C). Experimental results suggest that BaTiO doping improves the dielectric properties of the sintered BaSmTiO perovskite ceramics, which are further enhanced by doping with BaTiO in small amounts. However, further increase of BaTiO content jeopardizes them. [ABSTRACT FROM AUTHOR]