Abstract
A melilite Ba2CuGe2O7 ceramic was characterized by low sintering temperature and moderate microwave dielectric properties. Sintered at 960 °C, the Ba2CuGe2O7 ceramic had a high relative density 97%, a low relative permittivity (εr) 9.43, a quality factor (Q×f) of 20,000 GHz, and a temperature coefficient of resonance frequency (τf) −76 ppm/°C. To get a deep understanding of the relationship between composition, structure, and dielectric performances, magnesium substitution for copper in Ba2CuGe2O7 was conducted. Influences of magnesium doping on the sintering behavior, crystal structure, and microwave dielectric properties were studied. Mg doping in Ba2CuGe2O7 caused negligible changes in the macroscopic crystal structure, grain morphology, and size distribution, while induced visible variation in the local structure as revealed by Raman analysis. Microwave dielectric properties exhibit a remarkable dependence on composition. On increasing the magnesium content, the relative permittivity featured a continuous decrease, while both the quality factor and the temperature coefficient of resonance frequency increased monotonously. Such variations in dielectric performances were clarified in terms of the polarizability, packing fraction, and band valence theory.
Highlights
The development of wireless communication and broadband network technology has dramatically increased the demand for microwave dielectric materials,J Adv Ceram 2021, 10(1): 108–119 waves, and even terahertz bands [4,5]
The linear variation in lattice parameters validates the Vegard’s law for a solid solution. These results indicate the scheduled magnesium could completely dissolve into the lattice of melilite to form an infinite solid solution
The width of the 500 cm–1 and 258 cm–1 modes monotonously decreased with increasing Mg content, while the 775 cm–1 mode was firstly broadened and narrowed, resulting in the x = 0.4 composition featuring the highest full width at half maximum (FWHM). These results revealed that magnesium substitution induced local disorder, which becomes more distinct around x = 0.4
Summary
The development of wireless communication and broadband network technology has dramatically increased the demand for microwave dielectric materials,. Si-based melilites with a chemical formula [A2BSi2O7] have attracted intensive attention as microwave dielectric materials due to the ease with which the structures can accommodate different combinations of cations in the A and B sites [9,10,11]. Wang et al reported similar enhancement in sintering behavior and dielectric performances of Li3Mg2NbO6 by CuO doping [19]. This inspires us to investigate melilites which would further yield a reduction in sintering temperature and improvement in dielectric properties. Ba2CuGe2O7, a member of melilites, was studied on the dielectric properties at microwave frequencies with an attempt to explore novel materials as potential candidates for microwave communication. Doping effects on the sintering behavior, crystal structure, and microwave dielectric properties were studied
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