Effects of Calcium Substitution on the Structural and Microwave Dielectric Characteristics of [(Pb1−xCax)1/2La1/2](Mg1/2Nb1/2)O3 Ceramics |
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Authors: | Chin-Lin Liu Tai-Bor Wu |
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Affiliation: | Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan, Republic of China |
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Abstract: | The effects of calcium substitution on the structural and microwave dielectric characteristics of [(Pb1− x Ca x )1/2La1/2](Mg1/2Nb1/2)O3 ceramics (with x = 0.01–0.5) were investigated. All the materials were observed to have an ordered A(B1/2'B1/2")O3-type perovskite structure; however, the space group of the structure changed from Fm 3 m to Pa 3 as the calcium content increased to x = 0.1, and then from Pa 3 to R 3¯ at the x = 0.5 composition. During the structural evolution, the lattice parameter of the perovskite cell decreased linearly, and the dielectric constant ( k ) also decreased, from k = 80 to k = 38. However, the product of the quality factor and the resonant frequency ( Q × f ) increased from 50 000 GHz to 90 000 GHz as the calcium content increased. Also, the temperature coefficient of resonant frequency (τƒ) gradually changed from 120 ppm/°C to −40 ppm/°C as the calcium content increased. At the x = 0.3 composition, a combination of properties— k ∼ 50, Q × f ∼ 86 000 GHz, and τƒ∼ 0 ppm/°C—can be obtained. |
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Keywords: | dielectric materials/properties lead magnesium niobate substitution |
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