Assessment of crystallite size and strain of CaCu 3 Ti 4 O 12 (CCTO) with multimodal crystallite size is relatively a challenging task. Various estimation methods (Debye-Scherrer, Williamson-Hall, Rietveld refinement and Variance) are usually gave variation results due to different parameter selections of peaks broadening, for example, average line and integral breath (average and total). The high accuracy of estimation method is essential in order to obtain the best estimated result as close as possible to the observed crystallite size. Therefore, this Letter presents the comparison of estimation methods in determining the crystalline size and strain of CCTO from XRD peak broadening. The result shows that each method gave a different crystallite size as far as various solutions are concern and also depicts that the strain is same. However, Rietveld refinement, Debye-Scherrer and variance methods showed a highly correlated with domain size as observed from transmission electron microscopy analysis, due to an exclusion of the instrumental errors.
A wideband hybrid dielectric resonator antenna (DRA) consisting of a rectangular slot patch and a perforated stacked cylindrical dielectric resonator (DR) is proposed. A rectangular slot was etched on the grounding side of a microwave laminate ( =3.38) to excite the hybrid resonator at a high frequency. The stacked DR used consists of three different layers of permittivity, in which air-cavity was introduced internally to form a perforated structure. With a proper stacking arrangement of the perforated DRs on top of the rectangular slot, their operating frequencies were merged together to produce a wideband hybrid DRA. It was found that the combination of the stacked DR with perforated structure in the hybrid element had yielded an impedance bandwidth of as wide as 75.8% (12.2 GHz -27.1 GHz). Huge improvement in bandwidth was successfully achieved in this study in comparison to that without a perforated structure of only 48.9%. Simulation of the antenna was performed in time domain using Computer Simulation Technology (CST) and was subsequently verified with the measurement results. The average simulated and measured directivity of the antenna were recorded to be 6.05 dBi and 5.65 dBi, respectively, with a stable broadside radiation throughout the operating range of frequency. The radiation characteristics were seen to be broadside in both the E-plane and H-plane.INDEX TERMS wideband, hybrid dielectric resonator, perforated structure, Ku band, K band, cylindrical DR, rectangular slot patch.
The effect of calcination temperature on the properties of CaCu 3 Ti 4 O 12 (CCTO) ceramics was studied. CCTO ceramics were prepared using solid state reaction method. The raw materials of CCTO were wet mixed for 24 hours and was dried overnight. CCTO powders were then calcined at three different temperature which is at 900 o C, 930 o C and 985 o C for 12 hours. The calcined powders were compacted at 250 MPa and then were sintered at 1040 o C for 10 hours. X-Ray Diffractometer (XRD) analysis showed the formation of CCTO phase and secondary phases of CuO for C900 calcined powder but single phase of CCTO was obtained by C930 and C985 calcined powders. Single phase of CCTO also were seen for all sintered samples. Observation on Scanning Electron Microscopy (SEM) micrographs showed abnormal grain growth or large grain size was seen in C900 sample and finer grain size was observed for C930 and C985 sintered samples. C900 sintered sample obtained the highest dielectric constant (10,462) and the lowest dielectric loss (0.061) measured at 1 MHz.
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