# Temperature Stable, High-Quality Factor Li2 TiO3-Li4 NbO4F Microwave Dielectric Ceramics
## 3 Results and Discussion
Relatively small grains were observed for the compositions with x = 0.15 and 0.2, as shown in Figure 3c,d, which were likely due to the cubic phase grain, in agreement with the phase structure as shown in Figure 1 and Table 1.  
Figure 3: SEM micrographs of (1-x)Li\({}_{2}\)TiO\({}_{3}\)-xLi\({}_{4}\)NbO\({}_{4}\)F ceramics sintered at 1050 \({}^{\circ}\)C. (**a**) x = 0.05; (**b**) x = 0.10; (**c**) x = 0.15; (**d**) x = 0.20. Figure 2: Refined XRD pattern of 0.90 Li\({}_{2}\)TiO\({}_{3}\)-0.10 Li\({}_{4}\)NbO\({}_{4}\)F ceramics sintered at 1050 \({}^{\circ}\)C for 2 h.  
The EDS elemental mapping analysis of x = 0.05 and x = 0.20 for the ceramics sintered at 1050 \({}^{\circ}\)C for 2 h is given in Figures 4 and 5, respectively. It was obvious that F and Nb elements were heterogeneous in samples of x = 0.05, while elements were distributed homogeneously in samples of x = 0.20, which indicated that there were two phases of monoclinic and cubic phase coexistence in the sample of x = 0.05, whereas there was a one-phase solid solution in the sample of x = 0.20. The bulk densities of ceramics with different Li\({}_{4}\)NbO\({}_{4}\)F content as a function of sintering temperature are presented in Figure 6. In the range of x \(\leq\) 0.15, with the increase of the sintering temperature, the bulk densities originally increased slightly but later obviously decreased at 1100 \({}^{\circ}\)C, which revealed that the ceramics had overburnt behavior when sintered at 1100 \({}^{\circ}\)C. These results agreed with more and more pores observed in Figure 3, but the bulk density of the ceramics at x = 0.20 increased with the increase of sintering temperature. On the other hand, as the x content increased, the density decreased. Figure 4: SEM micrographs (**a**) of 0.95 Li\({}_{2}\)TiO\({}_{3}\)-0.05 Li\({}_{4}\)NbO\({}_{4}\)F ceramics sintered at 1050 \({}^{\circ}\)C for 2 h and corresponding EDS analysis surface scanning of (**b**) F element, (**c**) Nb element, (**d**) Ti element, and (**e**) O element. Figure 5: SEM micrographs (**a**) of 0.80 Li\({}_{2}\)TiO\({}_{3}\)-0.20 Li\({}_{4}\)NbO\({}_{4}\)F ceramics sintered at 1050 \({}^{\circ}\)C for 2 h and corresponding EDS analysis surface scanning of (**b**) F element, (**c**) Nb element, (**d**) Ti element, and (**e**) O element. Figure 7 displays the dielectric constant of samples sintered at various temperatures as a function of Li\({}_{4}\)NbO\({}_{4}\)F additions. With the increase of the sintering temperatures and Li\({}_{4}\)NbO\({}_{4}\)F content, the variations of \(\varepsilon_{\rm r}\) coincided with bulk density, which suggested that the density was the main external factor that affected \(\varepsilon_{\rm r}\) in the Li\({}_{2}\)TiO\({}_{3}\)-Li\({}_{4}\)NbO\({}_{4}\)F ceramics. It is well known that the \(\varepsilon_{\rm r}\) of ceramics is mainly determined by the dipoles in the unit cell volume and the dielectric polarizabilities of ions [25]. A higher density means that are more dipoles in a unit volume. As shown in Figure 3, more and more pores were observed in the range of x \(\leq\) 0.15, which lowered the density and further influenced \(\varepsilon_{\rm r}\). In this case, with the exception of the composition, the \(\varepsilon_{\rm r}\) of the Li\({}_{2}\)TiO\({}_{3}\)-Li\({}_{4}\)NbO\({}_{4}\)F samples was decided by bulk density, and the \(\varepsilon_{\rm r}\) of the 0.90 Li\({}_{2}\)TiO\({}_{3}\)-0.10 Li\({}_{4}\)NbO\({}_{4}\)F ceramics was 18.7 with a near-zero \(\tau_{\rm f}\) value, which was suitable for the application of the integrated circuit. The variation of the Q\(f\) value of the (1-x)Li\({}_{2}\)TiO\({}_{3}\)-xLi\({}_{4}\)NbO\({}_{4}\)F ceramics with different sintering temperatures is plotted in Figure 8. The Q\(f\) values decreased with the increase of  
Figure 6: Variation of bulk density of (1-x)Li\({}_{2}\)TiO\({}_{3}\)-xLi\({}_{4}\)NbO\({}_{4}\)F ceramics sintered at 1000–1125 \({}^{\circ}\)C for 2 h.  
Li\({}_{4}\)NbO\({}_{4}\)F content.