Characterization of structure and chemical bond in high-Q microwave dielectric ceramics LiM2GaTi2O8 (M = Mg, Zn)

摘要

LiM2GaTi2O8 (M = Mg, Zn) ceramics with the Fd-3m space group were synthesized using the solid-state method. In comparison with Mg2+ that fully occupied the tetrahedral (A) site in LiMg2GaTi2O8, LiM2GaTi2O8 was jointly occupied by Zn2+ and Li+ at the A site. Excellent microwave dielectric properties of Qxf = 133,400 +/- 500 GHz, 101,800 +/- 500 GHz, epsilon r = 17.1 +/- 0.2, 15.8 +/- 0.2, and tau f =-60.1 +/- 3.0 ppm/C, -42.2 +/- 3.0 ppm/C for LiM2GaTi2O8 and LiM2GaTi2O8 were obtained, respectively. The large deviations (30.3% for LiM2GaTi2O8 and 19.6% for LiZn2GaTi2O8) between the corrected epsilon corr and theoretical epsilon th were observed, which might be attributed to the underestimated Shannon's ionic polarizability of Ti4+ in Ti-containing spinels. Their intrinsic microwave dielectric properties were discussed based on bond valence, lattice energy (U), and B-site bond energy (E). Besides, their large negative tau f values were compensated to near-zero by CaTiO3.

关键词