## 3 Results and Discussion
### Structural and Microstructural Characterization
Figure 2: Raman spectra of KNL\(-\)(N0.9\(-\)xTSx) (\(x=0.00\) to 0.04) sintered samples (**a**), the position of the \(\upsilon\)1 band as a function of Sb concentration (**b**), and Raman shift evolution of the A1g Raman mode of the KNL\(-\)(N0.9\(-\)xTSx) ceramics as a function of x (**c**). Figure 4: EDS analysis on different points in the KNL–(N0.9\(-\)xTSx)ceramics with \(x=0.04\). Scale bar, 10 \(\upmu\)m. The table at the right presents the composition on the regions shown on a micrograph derived from EDS spectra. The table represents the atomic percentages of elements From the EDX analysis, the average compositions for the different points marked in Figure 4 could be calculated, obtaining compositions at points 1 and 3 (glassy phase), and at points 2 and 4 (main grains) of (K0.33 Na0.29 Li0.04)(Nb0.78 Ta0.18 Sb0.04)O3 and (K0.37 Na0.40 Li0.04)(Nb0.85 Ta0.11 Sb0.04)O3, respectively. Figure 3: Effect of Sb doping on microstructure. (**a**–**c**) FE-SEM images (with their respective grain size distributions, GSDs) showing the evolution of the microstructure in the KNL–(N0.9\(-\)xTSx)) ceramics as a function of the Sb content, where (**a**) corresponds to \(x=0.00\), (**b**) to \(x=0.02\), (**c**) to \(x=0.04\). Scale bar, 10 \(\upmu\)m. (**d**) Evolution of the average grain size with antimony addition. All samples exhibited a dense surface morphology, which was verified using Archimedes' method (see Table 1). Considering that high density values are required to obtain piezocer-ramics with good electrical properties, the high density values registered for the complete set of KNL\(-\)(N\({}_{0.9-x}\)TS\({}_{x}\))ceramic samples allow us to examine the dielectric, ferroelectric, and piezoelectric properties. Real permittivity and dielectric losses as a function of temperature (10 kHz) are shown in Figure 5. The curves present two phase transitions with temperature. The first one, near room temperature, can be assigned to the orthorhombic-tetragonal (T\({}_{\rm O-T}\)) phase transition, while the second, much clearer, one, between 300 to 400 \({}^{\circ}\)C, corresponds to the tetragonal-cubic (Tc) phase transition assigned to the ferroelectric-paraelectric transition. Furthermore, the Curie temperature (Tc), determined by the maximum of the dielectric constant, decreases when the Sb content increases (Figure 5b). In this way, the Tc value observed in the Sb-free sample (\(x\) = 0.00) was characteristic of K\({}_{0.5}\)Na\({}_{0.5}\)NbO\({}_{3}\) ceramics (-400 \({}^{\circ}\)C), while the Tc value for the maximum Sb content (\(x\) = 0.04) was close to that observed by [PERSON] et al. (290 \({}^{\circ}\)C) [27]. Similarly, the T\({}_{\rm O-T}\) phase transition follows the same trend. As observed in Figure 5a (marked in gray), the T\({}_{\rm O-T}\) drastically decreases with the Sb\({}^{+5}\) content, evidencing that this phase transition is clearly sensitive to the Sb\({}^{+5}\) content. However, this O-T phase transition is not enough clear because it is below or close to room temperature, depending on the \(x\) content. In addition, a slight widening of the Tc peak with Sb addition, due to an increase in the cation disorder in the perovskite structure, can be observed [28]. In short, considering the findings of both structural (Figures 1 and 2) and \(\epsilon_{r}\)-T curves (Figure 5), we can establish that the addition of Sb\({}^{5+}\) to the structure stabilizes the coexistence of the O and T phases at room temperature (with a predominance of the T phase). Finally, the dielectric loss diminution with antimony addition encourages the use of these compositions for possible dielectric applications.