Effects Of Lif On Crystal Structure, Cation Distributions And Microwave Dielectric Properties Of Mgal2o4

In this work, MgAl2O4 + xLiF (x = 0, 3.2, 6.4 mol. %) ceramics were synthesized by solid-state reaction method. The phase information of a spinel structure was delineated by XRD. The crystal structure of MgAl2O4 + xLiF (x = 0, 3.2, 6.4 mol. %) ceramics were discussed with the help of Rietveld refinements. As x increased from 0 to 6.4 mol. %, the tetrahedral sites in MgAl2O4 ceramics gradually were occupied by Al3+ cations, which is confirmed by Al-27 NMR and Raman spectra. Such the occupation of Al3+ cations increased the covalency (f(c)/s) value of M-O (M = Mg, Al) bond in MO4 tetrahedral of MgAl2O4 + xLiF (x = 0, 3.2, 6.4 mol. %) ceramics. LiF is mainly used as a sintering aid to improve the formation of the MgAl2O4 ceramics. In order to obtain high Qxf value spinel ceramics, LiF must be removed before the final stage of densification. In addition, the dielectric constant (epsilon(r)), grain size and quality factor (Qxf) value are significantly affected by the LiF content. However, the temperature coefficient of resonance frequency (TCf) values were independent of LiF content. MgAl2O4 + xLiF (x = 0, 3.2, 6.4 mol. %) ceramics with x = 6.4 has excellent microwave dielectric properties when sintered at 1575 degrees C for 8 h: epsilon(r) = 8.36, Qxf = 99,900 GHz, TCf = - 61.57 ppm/degrees C. (C) 2021 Elsevier B.V. All rights reserved.