Structure stability and microwave dielectric properties of double perovskite ceramics – Ba2Mg1−xCaxWO6 (0.0 ≤ x ≤ 0.15)
Structure stability and microwave dielectric properties of double perovskite ceramics – Ba2Mg1−xCaxWO6 (0.0 ≤ x ≤ 0.15)
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DOI：
10.1016/j.ceramint.2011.12.027
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发表时间：
2012-05
影响因子：
5.2
通讯作者：
J. Y. Wu;J. Bian
中科院分区：
文献类型：
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作者：
J. Y. Wu;J. Bian
用X射线粉末衍射仪、扫描电子显微镜和拉曼光谱研究了双钙钛矿陶瓷-Ba2Mg1−xCaxWO6(0≤x≤0 15)的结构稳定性。用网络分析仪研究了陶瓷在8-11 GHz频率范围内的微波介电性能。结果表明，少量的钙替代镁提高了镁/氧化钙的结合强度，从而提高了双钙钛矿的稳定性。但不能完全抑制Ba2Mg1−xCaxWO6在高温下的分解。虽然所有成分都采用空间群FM−3M，但由于阳离子大小差异较大，钙和镁离子在4b位上的分布在短程范围内是非随机分布的。Ca(x≤0.1)的小能级掺杂使介电常数单调增加，但对Q×f影响不大。正如预期的那样，钙的替代将谐振频率的温度系数(τf值)从负值调整为正值。当x=0.1时，可获得ɛr=20.8，Q×f=120,729 GHz，τf=0ppm/°C的综合微波介电性能。然而，当样品在环境条件下储存较长时间时，Q×f值会显著下降。
The structure stability of double perovskite ceramics – Ba2Mg1−xCaxWO6(0.0≤x≤0.15) has been studied by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and Raman spectrometry in this paper. The microwave dielectric properties of the ceramics were studied with a network analyzer at the frequency of about 8–11GHz. The results show that small amount of Ca substitution for Mg increases the Mg/CaO bond strength, and hence the stability of the double perovskite. But it cannot completely suppress the decomposition of Ba2Mg1−xCaxWO6at high temperature. Although space group Fm−3m is adopted for all compositions, nonrandom distribution of Ca2+and Mg2+on 4b-site within the short range scale is observed due to their large cation size difference. Small level doping of Ca (x≤0.1) increases the dielectric permittivity monotonically, but does not affect the Q×f value greatly. As expected, the substitution of Ca tuned the temperature coefficient of resonant frequency (τfvalue) from negative to positive value. Excellent combined microwave dielectric properties with ɛr=20.8, Q×f=120,729GHz, and τf=0ppm/°C could be obtained for x=0.1 composition. However the Q×f value degrades considerably when the sample was stored under ambient conditions for a long time.