Novel medium-entropy Ca <sub>3</sub>(Co <sub>0.25</sub>Zn <sub>0.25</sub>Mg <sub>0.25</sub>Cu <sub>0.25</sub>) <sub>2</sub>SiV <sub>2</sub>O <sub>12</sub> microwave dielectric ceramics with high <i>Q</i>× <i>f</i> and near-zero <i> <strong>τ</strong> </i> <sub>f</sub>
Junxian Wang, Yu‐Xuan Ren, Xiangkai Zhu, Yunfeng Guo, Jiamao Li
Abstract
In this paper, novel medium-entropy Ca<sub>3</sub>(Co<sub>0.25</sub>Zn<sub>0.25</sub>Mg<sub>0.25</sub>Cu<sub>0.25</sub>)<sub>2</sub>SiV<sub>2</sub>O<sub>12</sub> (CZMC) ceramics with garnet structure were designed and synthesized based on the entropy effect. Small average atomic-size difference was proved to be advantageous to forming the garnet structured solid solution, which was evidenced via X-ray diffraction (XRD) and Rietveld refinement results. The sintering temperature was effectively reduced due to an increase in the configurational entropy. The dielectric constant (ε<sub>r</sub>) of CZMC ceramics showed an opposite variation tendency to that of Raman shift at about 838 cm<sup>-1</sup> whereas the variation in the quality factor (<em>Q</em>×<em>f</em>) was identical to that of relative density but opposite to that of full width at half maximum (FWHM) of Raman spectra. The AC impedance spectroscopy manifested that the conductivity of CZMC ceramics was mainly from the diffusion of thermally activated oxygen vacancies. High activation energy further indicated low defect concentration in the sample contributed to reducing the dielectric loss of ceramics. The B-O bond showed the strongest contribution to the total bond energy, thus playing an important part in manipulating temperature coefficient of resonant frequency (τ<em><sub>f</sub></em>) of ceramics. Meanwhile, the V-O bond imparted significant influences on the ε<sub>r</sub> and the <em>Q</em>×<em>f</em> of CZMC ceramics. Finally, superior microwave dielectric properties (ε<sub>r</sub> = 10.89, <em>Q</em>×<em>f</em> = 59,200 GHz, and <em>τ<sub>f</sub></em> = –9.6 ppm/<sup> </sup><sup>o</sup>C) together with high relative density of 95.4% were achieved at 1010 <sup>o</sup>C. Therefore, an extensive application can be found in the field of millimeter wave communication for CZMC ceramics.