Microwave dielectric properties and microstructure of Ba6-3Nd8+2xTi18-y(Cr1/2Nb1/2)yO54 ceramics

The microwave dielectric properties and the morphology of Ba6-3xNd8+2xTi18-y(Cr1/2Nb1/2)(y)O-54 (x = 0.75, 0 <= y <= 3.0) ceramics prepared under different sintering conditions were investigated in this work. The effects of substitutions on the microstructure and microwave dielectric properties were discussed. The X-ray diffraction (XRD) patterns of the sintered samples revealed a single-phase formation BaNd2Ti4O12 with a tungsten bronze type structure in the system. The results of energy dispersive spectrometer (EDS) and lattice parameters calculated on XRD data could confirm the substitution at Bsite. A small amount of substitutions improved quality factor value (Q x f) and the temperature coefficient of resonant frequency (tau(f)) but led to a decrease of the permittivity. The temperature coefficient of resonant frequency (tau(f)) was found to decrease with increasing substitutions because of the declination of tolerance factor (t). And the tau(f) could be adjusted from +62.4 ppm/degrees C to -7.3 ppm/degrees C with increment of substitutions. Finally, excellent dielectric properties were obtained as y was 0.5 sintered at 1400 degrees C for 2 h in air: epsilon(r) = 88.6, Q x f = 11486 GHz, tau(f) = +37.1 ppm/degrees C. (C) 2015 Elsevier B.V. All rights reserved.