Layered-perovskite Ca1-xBaxLa4Ti5O17 microwave dielectric ceramics with medium dielectric constant
The layered perovskite Ca 1- x Ba x La 4 Ti 5 O 17 ( x = 0.2, 0.4, 0.6, 0.8) compounds were synthesized via the solid-state reaction method, and their phase composition, microstructure and microwave dielectric properties were investigated. X-ray diffraction (XRD), Raman spectroscopy and selected area electron diffraction (SAED) patterns confirmed that it appears as a single phase with orthorhombic perovskite structure belonging to the Pnnm space group when x = 0.2. The crystal structure analysis and high-resolution transmission electron microscope (HRTEM) results showed that the compound has a layered structure composed of 5 unit [TiO 6 ] layers tightly packed (A n B n O 3 n +2 , n = 5). The Q×f value of ceramics was gradually improved with the increase of Ba 2+ content, which was attributed to the production of the second phase BaLa 2 Ti 3 O 10 , but it also caused the deviation of the temperature coefficient of resonant frequency (τ f ). For the ceramic specimen of x = 0.2, excellent microwave dielectric properties were obtained with an optimal combination ( ε r = 57.2, Q×f = 12,100 GHz, and τ f = 0.67 ppm/°C). Ba-modified CaLa 4 Ti 5 O 17 ceramics with comprehensive and excellent performance provides support for miniaturized microwave device applications.
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