## 3 Results and Discussion  
Figure 1 shows the XRD patterns of the MSO powders calcined at different temperatures. As can be seen from Figure 1a, the MSO phase (ICDD 01-074-0714) was discovered in all the samples, combined with the secondary phases identified as MgSiO\({}_{3}\) and MgO, which decreased with the increase in calcining temperature, as shown in Figure 1b,c. The SiO\({}_{2}\) phase was detected when the powders were calcined at 1250 \({}^{\circ}\)C, while there was no SiO\({}_{2}\) phase when the powders were calcined at temperatures more than 1250 \({}^{\circ}\)C. Thus, it was too troublesome to obtain the composition of the pure MSO phase by the conventional solid-state method, as the MgSiO\({}_{3}\) phase and residual MgO phase always emerged, induced by a small amount of amorphous SiO\({}_{2}\) at high temperatures [26]. When the calcining temperature increased, the residual MgO reacted with MgSiO\({}_{3}\), leading to an increase in the MSO phase [26]. Considering many clumps in the MSO powders calcined at 1400 \({}^{\circ}\)C, the optimum calcining temperature was selected as 1350 \({}^{\circ}\)C for the MSO powders in this work. Figure 2a shows the XRD patterns of the MLLC ceramics sintered at 800 \({}^{\circ}\)C. A principal crystalline phase identified as Mg\({}_{2}\)SiO\({}_{4}\) (ICDD 01-074-0714) was detected for all the samples. The secondary phases could be identified as LiTiO\({}_{2}\), SiO\({}_{2}\), Li\({}_{2}\)TiO\({}_{3}\), Li\({}_{2}\)MgSiO\({}_{4}\), and CaTiO\({}_{3}\). No LiF phase was discovered from the XRD patterns of the MLLC ceramics, which could be attributed to the solid solution formation between Li\({}_{2}\)TiO\({}_{3}\) and LiF [35]. Due to this solid solution, Li\({}^{+}\) and F\({}^{-}\) ions entered into Li\({}_{2}\)TiO\({}_{3}\) lattice and formed the LiTiO\({}_{2}\) phase, which could also be produced in ceramic systems with an excess MgO content [36; 37]. The  
Figure 1: XRD patterns of the MSO powders calcined at different temperatures. (**a**) 10\({}^{\circ}\)–80\({}^{\circ}\), (**b**) 26.5\({}^{\circ}\)–29.5\({}^{\circ}\), and (**c**) 42.5\({}^{\circ}\)–43.25\({}^{\circ}\). phases of MgSiO\({}_{3}\), MgO, and amorphous SiO\({}_{2}\) react with Li\({}_{2}\)TiO\({}_{3}\), leading to the formation of Li\({}_{2}\)MgSiO\({}_{4}\) and LiTiO\({}_{2}\), according to the following reactions:  
\[2\mathrm{Li}_{2}\mathrm{TiO}_{3}+\mathrm{MgO}+\mathrm{SiO}_{2}\to\mathrm{Li}_{ 2}\mathrm{MgSiO}_{4}+2\mathrm{LiTiO}_{2}+\frac{1}{2}\mathrm{O}_{2}\uparrow \tag{3}\]  
\[2\mathrm{Li}_{2}\mathrm{TiO}_{3}+\mathrm{MgSiO}_{3}\to\mathrm{Li}_{2} \mathrm{MgSiO}_{4}+2\mathrm{LiTiO}_{2}+\frac{1}{2}\mathrm{O}_{2}\uparrow \tag{4}\]  
As shown in Figure 2a, the CaTiO\({}_{3}\) phase existed in the ceramic systems in the form of the secondary phase without reaction with other phases. Rietveld refinements using Fullprof software were introduced to confirm the weight percentage and the theoretical density of each phase in the MLL ceramic without CaTiO\({}_{3}\), as shown in Figure 2b. The ion occupancy was revised based on the crystal structures of Li\({}_{2}\)MgSiO\({}_{4}\), SiO\({}_{2}\), Li\({}_{2}\)TiO\({}_{3}\), LiTiO\({}_{2}\), and Mg\({}_{2}\)SiO\({}_{4}\). The XRD pattern of the MLL ceramic displayed good refinement. The refinement result is shown in Table 1. The theoretical density of the MLL ceramic was calculated according to Equation (1), with a value of about 3.381 g/cm\({}^{3}\). As CaTiO\({}_{3}\) could not react with the MLL, the theoretical densities of the MLLC ceramics could also be calculated according to Equation (1). Figure 3 shows the SEM micrographs of the cross-sections of the MLLC ceramics sintered at 800 \({}^{\circ}\)C. No grain changes were discovered for any of the samples when increasing the CaTiO\({}_{3}\) content. Some pores were detected for the MLL ceramic, and a dense microstructure was detected for all the samples with CaTiO\({}_{3}\) additives, which indicated that CaTiO\({}_{3}\) additives could promote the densification of the MLLC ceramics.