# Temperature Stable, High-Quality Factor Li2 TiO3-Li4 NbO4F Microwave Dielectric Ceramics
## 3 Results and Discussion
The maximum _Qf_ value of 76,202 GHz was achieved for the 0.95 Li\({}_{2}\)TiO\({}_{3}\)-0.05 Li\({}_{4}\)NbO\({}_{4}\)F ceramics sintered at 1100 \({}^{\circ}\)C. The desired ceramics with a near-zero \(\tau_{\rm f}\) and high Qf value of 61,388 GHz were acquired for the 0.90 Li\({}_{2}\)TiO\({}_{3}\)-0.10 Li\({}_{4}\)NbO\({}_{4}\)F ceramics sintered at 1050 \({}^{\circ}\)C, which was near to that of the pure Li\({}_{2}\)TiO\({}_{3}\) (63,500 GHz). Compared with nonlithium-based ceramics, the Li\({}_{2}\)TiO\({}_{3}\)-Li\({}_{4}\)NbO\({}_{4}\)F ceramics and other lithium-based ceramics exhibited a relatively high Qf and low \(\varepsilon_{\rm r}\) as shown in Figure 3.0 At x = 0.15 and x = 0.20, the Qf value increased linearly with the increase of the sintering temperature without the downward trend because the ceramics with the cubic phase need a higher sintering temperature than the ceramics with the monoclinic phase [26]. Microstructural defects, grain boundaries, porosity, and microcracks usually play important roles in dielectric loss [27]. As mentioned in Figure 3, more pores were observed in the 0.90 Li\({}_{2}\)TiO\({}_{3}\)-0.10 Li\({}_{4}\)NbO\({}_{4}\)F ceramics than in the 0.95 Li\({}_{2}\)TiO\({}_{3}\)-0.05 Li\({}_{4}\)NbO\({}_{4}\)F ceramics, which was consistent with the decrease of Qf. Figure 9 shows the variation of the \(\tau_{\rm f}\) value of the (1-x)Li\({}_{2}\)TiO\({}_{3}\)-xLi\({}_{4}\)NbO\({}_{4}\)F ceramics. \(\tau_{\rm f}\) was well known to be influenced by the composition, additive, and second phase of the materials [35]. With the increase of x, \(\tau_{\rm f}\) showed a negative trend. At x = 0.10, the 0.9 Li\({}_{2}\)TiO\({}_{3}\)-0.11 Li\({}_{4}\)NbO\({}_{4}\)F ceramics sintered at 1050 \({}^{\circ}\)C for 2 h achieved a \(\tau_{\rm f}\) of 0.9 ppm/\({}^{\circ}\)C, which is very important for applications. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Material** & \(\varepsilon_{\rm r}\) & **Qf (GHz)** & \(\tau_{\rm f}\) (ppm/\({}^{\circ}\)C) &
\begin{tabular}{c} **Sintering** \\ **Temperature (\({}^{\circ}\)C)** \\ \end{tabular} & **Reference** \\ \hline Ba\({}_{1.85}\)Ca\({}_{0.15}\)MgTi\({}_{5}\)O\({}_{13}\) & 29.3 & 30,870 & +2.1 & 1160 & [28] \\ NiZrNb\({}_{2}\)O\({}_{8}\) & 23.77 & 40,280 & \(-\)27.5 & 1200 & [29] \\ Ca\({}_{3}\)Sn\({}_{0.95}\)Ti\({}_{0.05}\)Si\({}_{2}\)O\({}_{9}\) & 11.07 & 42,400 & \(-\)5.1 & 1325 & [30] \\ ZnTiNb\({}_{2}\)O\({}_{8}\) & 35.5 & 52,500 & \(-\)60 & 1050 & [31] \\
0.9 Li\({}_{2}\)TiO\({}_{3}\)-0.11\({}_{4}\)NbO\({}_{4}\)F & 18.7 & 61,388 & +0.9 & 1050 & this work \\ Li\({}_{2}\)TiGeO\({}_{5}\) & 9.43 & 65,300 & +24.1 & 1140 & [32] \\ Li\({}_{3}\)Mg\({}_{2}\)Sb\({}_{0}\) & 10.5 & 84,600 & -9.0 & 1300 & [33] \\ Li\({}_{2}\)Mg\({}_{2.88}\)Ca\({}_{0.12}\)TiO\({}_{6}\) & 17.8 & 102,246 & \(-\)0.7 & 1280 & [34] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Microwave dielectric properties of nonlithium and lithium-based microwave dielectric ceramics. Figure 8: Quality factor of (1-x)Li\({}_{2}\)TiO\({}_{3}\)-xLi\({}_{4}\)NbO\({}_{4}\)F ceramics sintered at 1000–1125 \({}^{\circ}\)C for 2 h.