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Effect of CdO Addition on Microwave Dielectric Properties of Ba_xSr_1-xTiO₃ Ceramics

Doaa A. Abdel Aziz, Wagdy N. Nour, Aisha E. Reda, Eglal R. Souya

Journal of Ceramic Science and Technology, Vol. 1, No. 1 (2010), pp. 41-50

DOI: 10.4416/JCST2010-00001

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Abstract

Ceramic-based barium strontium titanate (BST) solid solutions with the formula BaxSr1-xTiO3 are very important candidates for millimetre-wave applications (e.g. filters and antennas). Several samples with and without CdO were prepared by means of the conventional solid-state route. Five compositions with (0.00 ≤ × ≤ 0.30) sintered at temperatures in the range 1300 - 1500 °C were investigated. Structural X-ray diffraction analysis confirmed their perovskite structure. The morphology of the sintered ceramic bodies was analysed by means of scanning electron microscopy (SEM) and energy-dispersive X-ray (EDAX) microanalysis. The cavity resonance method was used to measure the dielectric properties at microwave (MW) frequency range 40 MHz – 8 GHz. The results revealed that the microwave dielectric characteristics were strongly affected by different Ba/Sr ratios, the cadmium concentration and the microstructure developed. The addition of CdO (0.10, 0.15 and 0.20 mol %) to BaxSr1-xTiO3 ceramic bodies decreased the sintering temperature, with optimum density being obtained at 1400 °C. The best combination of microwave dielectric characteristics was obtained for BST10 ceramic with 0.20 mol % CdO sintered at 1400 °C/2 h, with dielectric constant (εr) = 291, low dielectric loss = 0.0005 and quality factor (Q × ƒ) = 3281 at 1.8 GHz). This can be attributed to its uniform grain morphologies and fine-grained (≤ 0.1 μm) crystalline phases that are round in shape.

Keywords

microwave, dielectric properties, microstructure, SrO, BaO, TiO2 and CdO

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