Journal
CERAMICS INTERNATIONAL
Volume 48, Issue 20, Pages 29929-29937Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.ceramint.2022.06.259
Keywords
Microwave dielectric ceramics; Additive; Structure-property relationships; Lattice vibrational characteristics; Dielectric response
Categories
Funding
- National Natural Science Foundation of China [11874240]
- Natural Science Foundation of Shandong Province [ZR2020QA047, ZR2021ME176]
- Project of Innovation Team in Jinan City for Universities [2021GXRC063]
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This study prepared CaWO4-x wt.% LiF microwave dielectric ceramics through solid-state reaction and investigated the effects of LiF content on their dielectric properties and lattice vibration characteristics. The results showed that LiF can form a liquid phase and increase the compactness of the ceramics, resulting in an increase in quality factor and a decrease in dielectric constant. The study on lattice vibration characteristics revealed that the external modes associated with Ca-O bond vibration have the greatest influence on the dielectric response.
In this paper, CaWO4-x wt.% LiF (x = 0.5-3.0) microwave dielectric ceramics are prepared by conventional solid-state reaction at 850 ?. All the X-ray diffraction peaks are attributed to CaWO4, combined with the results of X-ray photoelectron spectroscopy and scanning electron microscope. They indicate that LiF forms liquid phase at high temperature, exists in amorphous phase, and the CaWO4-x wt.% LiF samples belong to the composite ceramics. With the increase of the LiF content, the liquid phase fills the pores of the ceramics and increases the compactness. Therefore, the quality factor increases from 59,055 GHz (x = 0.5) to 77,855 GHz (x = 3.0), and the dielectric constant decreases from 9.26 (x = 0.5) to 8.41 (x = 3.0). The lattice vibration characteristics of the CaWO4-x wt.% LiF samples are studied by Raman and infrared spectroscopy. The external modes associated with the vibration of the Ca-O bonds have the greatest influence on the dielectric response, as shown by the fitting results based on the four-parameter semi-quantum (FPSQ) model. In addition, the simulated intrinsic properties and measured values are in general agreement. When the x value increases, the dielectric constant decreases with the decrease of the bond length. The quality factor has a negative correlation with the FWHM value of the B-g mode and a positive correlation with the packing fraction. Finally, the CaWO4-3 wt.% LiF sample has good compatibility with the silver powders at 850 ?, and high application value in the LTCC field.
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