Search

A novel BaMgSi4O10 ceramic was fabricated using a conventional solid-state method. The BaMgSi4O10 accompanied with BaMgSiO5, Ba2MgSi2O7, and SiO2 was detected for all compositions. Furthermore, microwave dielectric properties with εr = 5.7,Q × f = 17,900 GHz, and τf = − 19.1 ppm/°C were obtained at 1100 °C. To meet the requirement of LTCC technology, the optimum temperature can be lower than 850 °C by composing with 2 wt% LMS glass with a short soaking time of 0.5 h. A patch antenna was fabricated using BaMgSi4O10-2 wt% LMS as the substrate with a bandwidth of 120 MHz at 4.12 GHz. All result indicates BaMgSi4O10-2 wt% LMS ceramic has large application prospect in wireless communication systems. [ABSTRACT FROM AUTHOR]

In this study, we synthesized BaZnSi3O8‐based compounds with monoclinic structures (P21/a) using a solid‐state method. The crystal structure, phase composition, and microwave dielectric properties of BaZnSi3O8‐based ceramics were systematically investigated systematically. X‐ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images proved that the maximum solubility of BaZn1‐xMgxSi3O8 ranged between 0.3 and 0.4. Rietveld refinement and Phillips–Van Vechten–Levine complex chemical bond theory were used to illustrate the relationship between the microwave dielectric performance and lattice parameters. To further improve the properties, we substituted Ba2+ with Sr2+ in BaZn0.8Mg0.2Si3O8. Ba1‐ySryZn0.8Mg0.2Si3O8 remained in a single‐phase as y increased from 0 to 1.0. We achieved thermal stability of the resonance frequency of the BaZnSi3O8‐based ceramics by adjusting TiO2 to form composite ceramics. After sintering at 1020°C for 5 h, excellent microwave dielectric properties with εr = 7.44, Q×f = 57,400 GHz, and τf = − 0.2 ppm/°C were realized in the SrZn0.8Mg0.2Si3O8+8 wt %TiO2 system. [ABSTRACT FROM AUTHOR]

Novel BaCa2M3O9 (M = Si, Ge) microwave dielectric ceramics were prepared via solid‐state reaction with sintering at 1125°C–1275°C for 5 h. Single‐phase BaCa2M3O9 (M = Si, Ge) ceramics were obtained according to stoichiometry. The single‐phase BaCa2Ge3O9 ceramic was confirmed through Rietveld refinement and high‐resolution transmission electron microscopy/selected area electron diffraction and synthesized for the first time. The BaCa2M3O9 (M = Si, Ge) exhibited a triclinic structure with a P1¯$\bar 1$ space group and good microwave dielectric properties. The εr, Q × f, and τf values of BaCa2M3O9 (M = Si, Ge) ceramics are mostly dominated by the relative density, ionic polarizability, relative covalence, and bond energy of M–O bond, respectively. A high Q × f value (61 800 GHz at 16.3 GHz) was obtained in BaCa2Ge3O9 ceramic due to its high rc (Ge–O) and low intrinsic dielectric loss. The BaCa2Si3O9 ceramic exhibited small |τf| value (‒36.4 ppm/°C) due to its large ESi‐O. Excellent microwave dielectric properties (εr = 8.31, Q × f = 61 800 GHz, and τf = ‒58.7 ppm/°C) were obtained for the BaCa2Ge3O9 ceramic. [ABSTRACT FROM AUTHOR]

The dielectric properties of a Ga‐based melilite type ceramic Sr2Ga2SiO7 via theoretical prediction based on far‐infrared spectroscopy and experimental measurement by the Hakki–Coleman method were studied in this work. Dense and single‐phase ceramics were fabricated via solid‐state reaction at 1330°C and exhibited comprehensive microwave dielectric properties (εr ∼ 7.6, Q × f ∼ 23 600 GHz, and τf ∼ −35.2 ppm/°C) at 14.3 GHz. Chemical modifications were proposed to adjust the thermal stability and reduce the densification temperature. By adding 10 mol% CaTiO3, the negative τf can be compensated to a near‐zero value of −3.8 ppm/°C. The densification temperature was reduced to 940°C by adding 3 wt.% LiF. A patch antenna was designed using Sr2Ga2SiO7 ceramic with a high radiation efficiency of 99.1% and a gain of 2.788 dBi at the center frequency of 4.371 GHz. All results indicate that the Sr2Ga2SiO7 ceramic has promising application potential for 5G wireless communication technology. [ABSTRACT FROM AUTHOR]

BaSixO1+2x (1.61 ≤ x ≤ 1.90) and LiF-doped BaSi1.63O4.26 ceramics were prepared by using a traditional solid-state method at the optimal sintering temperatures. The evolution of phase compositions of BaSixO1+2x (1.61 ≤ x ≤ 1.9) ceramics was revealed. The coexistence of Ba5Si8O21 and Ba3Si5O13 phases was obtained in BaSixO1+2x (1.61 ≤ x ≤ 1.67) ceramics. The BaSi2O5 phase appeared inBaSixO1+2x (1.68 ≤ x ≤ 1.90) ceramics. At 1.68 ≤ x ≤ 1.69, only BaSi2O5 and Ba3Si5O13 phases existed. With the further increase in x, the Ba5Si8O21 phase appeared, and BaSi2O5, Ba5Si8O21 and Ba3Si5O13 phases coexisted in BaSixO1+2x (1.70 ≤ x ≤ 1.90) ceramics. The phase compositions of BaSixO1+2x (1.61 ≤ x ≤ 1.90) ceramics were controlled by the ratio of Ba:Si. The BaSixO1+2x (x = 1.68) ceramics with 98.15 wt% Ba3Si5O13 and 1.85 wt% BaSi2O5 phases exhibited a negative τf value (−37.53 ppm/°C), and the good microwave dielectric properties of εr = 7.51, Q × f = 13,038 GHz and τf = +3.95 ppm/°C were obtained for BaSi1.63O4.26 ceramics with 70.05 wt% Ba5Si8O21 and 29.95 wt% Ba3Si5O13 phases. The addition of LiF sintering aids were able to reduce the sintering temperatures of BaSi1.63O4.26 ceramics to 800 °C. The phase composition of BaSi1.63O4.26 ceramics was affected by the sintering temperature, and the coexistence of Ba5Si8O21, Ba2Si3O8, BaSi2O5 and SiO2 phases was achieved in BaSi1.63O4.26-3 wt% LiF ceramics. The BaSi1.63O4.26-3 wt% LiF ceramics sintered at 800 °C exhibited dense microstructures and excellent microwave dielectric properties (εr = 7.10, Q × f = 12,463 GHz and τf = +5.75 ppm/°C), and no chemical reaction occurred between BaSi1.63O4.26-3 wt% LiF ceramics and the Ag electrodes, which indicates their potential for low-temperature co-fired ceramic (LTCC) applications. [ABSTRACT FROM AUTHOR]

The traditional solid‐state reaction method was used to prepare Ca2Sn2−xMxAl2O9 (M = Ti, Zr, and Hf) ceramics. Then, the impact of an M4+ substitution of Sn4+ on the phase transition, crystal structural parameter, and microwave dielectric properties of Ca2Sn2−xMxAl2O9 (0 ≤ x ≤ 0.4) ceramics were investigated. Ti4+ could not replace the Sn4+ of Ca2Sn2Al2O9 due to its small ionic radius, and the Al‐based second phases of Ca2Sn2−xTixAl2O9 ceramics were confirmed by the X‐ray diffractometer and EDS map scanning results. With the Zr4+ and Hf4+ substitutions of Sn4+, the SnO2 and CaSnO3 second phases of Ca2Sn2Al2O9 ceramic were inhibited, and the Ca2Sn2−xMxAl2O9 (M = Zr and Hf) (0.05 ≤ x ≤ 0.2) single‐phase ceramics with orthorhombic structure (Pbcn space group) were obtained. New MO2 (M = Zr and Hf) and CaAl2O4 second phases appeared in the Ca2Sn2−xMxAl2O9 (M = Zr and Hf) (0.3 ≤ x ≤ 0.4) ceramics, and their contents increased gradually with the increase in x. The Ca2Sn2−xMxAl2O9 (M = Zr and Hf) (0.05 ≤ x ≤ 0.2) ceramics exhibited high Q × f because of their pure phase compositions, and the Q × f of Ca2Sn2Al2O9 ceramic was improved to 77 800 GHz (12.6 GHz) in the Ca2Sn1.9Zr0.1Al2O9 ceramic. The Q × f values of Ca2Sn2−xMxAl2O9 single‐phase ceramics were mainly controlled by rc (Sn/M–O) and rc (Al–O). The τf values of single‐phase Ca2Sn2−xMxAl2O9 ceramics were related to octahedral distortions. The Zr4+ and Hf4+ substitution of Sn4+ optimized the phase compositions and microwave dielectric properties of the Ca2Sn2−xMxAl2O9 ceramics, and the Ca2Sn1.9Zr0.1Al2O9 ceramic sintered at optimal temperature exhibited excellent microwave dielectric properties (εr = 8.67, Q × f = 77 800 GHz at 12.6 GHz and τf = −69.8 ppm/°C). [ABSTRACT FROM AUTHOR]

A novel composite ceramic with low densification temperature was fabricated using the conventional solid-state method. The XRD and Rietveld refinement results indicated that the two phases of CaB2O4 and CaSiO3 can coexist in all compositions. Furthermore, a phase transition of CaSiO3 ceramic from α-phase to β-phase was observed. A dense ceramic with excellent microwave dielectric properties (εr~6.4, Q × f~75,600 GHz, and a negative τf~26.9 ppm/°C) was obtained at x = 0.5 when sintered at 925 °C at the frequency of 14.2 GHz. A good chemical compatibility between the composite ceramic and Ag electrode was improved by elemental mapping results. A patch antenna was fabricated based on the simulated result. All results indicated that the 0.5 CaB2O4 + 0.5 CaSiO3 ceramic has large application potential in the LTCC field. [ABSTRACT FROM AUTHOR]