Microwave dielectric properties of spinel-structured Li0.5Ga2.5O4 ceramics with cation ordering on octahedral sites

Abstract The effect of firing temperature on the cation distributions of Li + and Ga 3+ in the tetrahedral and octahedral sites of Li 0.5 Ga 2.5 O 4 ceramics was investigated and the microwave dielectric properties of the ceramics were also characterized in this study. 7 Li and 71 Ga solid-state nuclear magnetic resonance (NMR) spectra revealed the preferential occupations of the Ga 3+ cations in tetrahedral sites of the Li 0.5 Ga 2.5 O 4 ceramics, whereas the octahedral sites of the ceramics were occupied by the Li + and Ga 3+ cations. Moreover, the order/disorder behavior of Li + and Ga 3+ cations on the octahedral sites was examined by Raman spectroscopy and crystal structure refinements; the fractions of disordered ( Fd 3 m ) Li 0.5 Ga 2.5 O 4 ceramic increased from 0.9 to 10.3%, depending on the firing temperature. From this result, it is considered that the coexistence of the ordered ( P 4 3 32) and disordered Li 0.5 Ga 2.5 O 4 ceramics is suggested. As a result, the covalency of the cation–oxygen bonds in the GaO 4 tetrahedron and M O 6 octahedron ( M = Li + and Ga 3+ ) was strongly affected by the order/disorder behavior of the Li + and Ga 3+ cation in the tetrahedral and octahedral sites. The ε r of the ceramics increased from 6.1 to 10.1 with increasing firing temperature, depending on the relative density and fraction of the disordered phase. Q · f also markedly improved from 18,546 to 237,962 GHz.