Structure and Microwave Dielectric Characteristics of Ca1+xNd1−xAl1−xTixO4 Ceramics
CaNdAlO4 microwave dielectric ceramics were modified by Ca/Ti co-substitution, and their dielectric characteristics were evaluated along with their structure and microstructures. Ca1+xNd1−xAl1−xTixO4 (x=0, 0.025, 0.05, 0.10, 0.15, 0.20) ceramics with the relative density of over 95% theoretical density were obtained by sintering at 1400°–1450°C in air for 3 h, where the K2NiF4-type solid solution single phase was determined from the compositions of x<0.20, while a small amount of CaTiO3 secondary phase was detected for x=0.20. With Ca/Ti co-substitution in CaNdAlO4 ceramics, the dielectric constant (r) increased with increasing x, and the temperature coefficient of resonant frequency (f) was adjusted from negative to positive, while the Q×f0 value increased significantly at first and reached an extreme value at x=0.025 and the maximum at x=0.15. The best combination of microwave dielectric characteristics were achieved at x=0.15 (r=19.5, Q×f0=93 400 GHz, f=−2 ppm/°C). The improvement of the Q×f0 value primarily originated from the reduced interlayer polarization with Ca/Ti co-substitution, while the decreased tolerance factor, the subsequent increased interlayer stress, and the appearance of CaTiO3 secondary phase brought negative effects upon the Q×f0 value.
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Document Type: Research Article
Affiliations: Laboratory of Dielectric Materials, Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China
Publication date: October 1, 2009