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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]

B-site oxide precursor method was utilized to synthesize Ba3MgNb2O9 ceramics. The effects of sintering temperature on phase composition of Ba3MgNb2O9 ceramics was evaluated by the X-ray diffraction. Experimental results indicated that all prepared Ba3MgNb2O9 ceramics exhibited 1:2 ordered hexagonal structure. The second phase Ba5Nb4O15 can emerge in all ceramics due to the decrease of activation energy of reaction, leading to the splitting of Eg(O) vibration mode in the Raman spectra. In addition, lattice parameters of 1:2 ordered phase were obtained from the refinement of XRD patterns. The maximum value of c/a ratio occurred at 1475 °C, meanwhile the ceramics showed the highest 1:2 ordered degree and excellent Q × f. It was also found that the uniform grain-size distribution of Ba3MgNb2O9 powder were important factors for preparing dense Ba3MgNb2O9 ceramics. Moreover, B-site oxide precursor method can not only effectively lower the densification temperature from 1650 to 1475 °C, but also increase the quality factor (Q × f) by about 90.8%, i.e., from 55,277 to 105,467 GHz. [ABSTRACT FROM AUTHOR]

Ceramics joining has been widely applied in MEMS sensors, microwave and imaging devices as well as other ceramic packaging applications to fabricate multifunctional ceramic components. In this study, a glass frit with gradient thermal expansion coefficient (TEC) has been applied as the bonding material to join the ceramic of Al 2 O 3 and AlN. This glass frit consists of two types of glasses with different TEC. The Al 2 O 3 and AlN ceramics have been successfully joined with this glass frit in muffle furnace at 850 °C for 1 h. The bonding strength of Al 2 O 3 /AlN ceramic joined via this glass frit exceeds 40 MPa without any cracks in the joining interface, which is much superior compared with that of conventional glass frit bonding. Our work demonstrates that the gradient-TEC glass frit bonding is an effective method to join different types of ceramics. [ABSTRACT FROM AUTHOR]

PbO–ZnO–B 2 O 3 (PZB) glass with low-melting temperature has been widely applied in microelectromechanical systems (MEMS) packaging. However, the high thermal expansion coefficient (TEC) of PZB glass usually leads to strict packaging requirements. Here, in order to achieve ideal TEC, we have introduced β -eucryptite into PZB/ β -eucryptite composite glass and optimized the composite fabrication process. Firstly, PbO:ZnO:B 2 O 3 in mol ratio of 65:15:20 was selected as glass matrix owing to its low-melting temperature and good wettability. Then, β -eucryptite ceramics with ultra-low TEC were synthesized via a facile solid-state reaction method to optimize subsequent composite TEC value. The combination of corresponding material and device characterizations suggest that the pure phase and regular columnar grains of β -eucryptite ceramic can be obtained by sintering at 1450 °C for three hours, which can result in the lowest negative TEC of α 30-300°C = −10.74 × 10−6 K−1. Furthermore, regarding the PZB/ β -eucryptite composite glasses, systematic experiments demonstrated that the β -eucryptite introduction can greatly impact the TEC of matrix glass with only negligible effect on the softening point (T s). Importantly, composite glasses with TEC of α 30-300°C = 3.26 × 10−6 K−1, T s = 380 °C and wetting angle < 30° are ideal for MEMS packaging. This work implements optimized fabrication process to obtain low-melting PZB/ β -eucryptite composite glasses with ideal TEC values, which can be envisaged to be applied in advanced MEMS packaging applications. [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]

BaO-Sm 2 O 3 –5TiO 2 (BST) added by Al 2 O 3 was prepared by solid-state reaction method. The main phase is Ba 3.99 Sm 9.34 Ti 18 O 54 of orthorhombic tungsten bronze structure, and the secondary phase is Ba 1.18 Al 1.90 Ti 6.09 O 16 of tetragonal structure, which has two types of grains: one is grey and cubic, and the other is white and quasi-rectangular. Microstructure was characterized by XRD, SEM, and Raman spectra. Micromechanical properties of different phases were assessed by nanoindentation and micro-scratch tests with Berkovich indenter. Volume fractions of different phases obtained by statistical analysis of grid indentation are in good agreement with those obtained by XRD analysis. Vickers hardness method is more appropriate for the determination of the fracture toughness of dielectric ceramics. BST ceramic without addition of Al 2 O 3 has better mechanical properties than BST-A with addition of Al 2 O 3 , indicating that addition of Al 2 O 3 impairs the micromechanical properties of dielectric ceramics. [ABSTRACT FROM AUTHOR]

Dense AlN ceramics with a thermal conductivity of 180W/m·K were obtained at the sintering temperature of 1750 °C using CaF2 and YF3 as additives. At temperatures below 1650 °C, the shrinkage of AlN ceramics is promoted by liquid (Ca,Y)F2 and Ca12Al14O32F2. Liquid CaYAlO4 mainly improves the densification of the sample when the sintering temperature increases to 1750 °C. The formation of liquid (Ca,Y)F2 at a relatively low temperature results in homogeneous YF3 distribution around the AlN particles, which benefits the removal of oxygen impurity in the AlN lattice, and thus a higher thermal conductivity. [Copyright &y& Elsevier]