## 4 Conclusions  
The study examined the effect of La\({}^{3+}\) doping on (Pb\({}_{0.75}\)Ba\({}_{0.25}\))(Zr\({}_{0.70}\)Ti\({}_{0.30}\))O\({}_{3}\)(PBZT) ceramics, which were obtained using the conventional solid-state synthesis method. The structure and morphology of the ceramics were analyzed using scanning electron microscopy and energy dispersive X-ray spectroscopy. The results indicate that the chemical composition of the ceramic samples corresponded to the initial stoichiometry of the ceramic powder. An increase in lanthanum content led to a decrease in the average grain size of the ceramics. Additionally, X-ray diffraction analysis confirmed that the structure of PBZT and PBZT doped with La\({}^{3+}\) at concentrations of \(x=1\) at.% and \(x=2\) at.% was rhombohedral (R3c space group), while for PBZT doped with La\({}^{3+}\) at concentrations \(x=3\) at.% and \(x=4\) at.%, the dominating phase was cubic (Pm-3m space group), with about 30% admixture of a remnant rhombohedral component. The electrical properties were investigated using impedance spectroscopy over a wide range of temperatures and frequencies. A detailed analysis of the obtained results revealed an increase in grain and grain boundary resistivity caused by lanthanum modification. The results are in good agreement with the thermally stimulated depolarization current measurements presented earlier and confirm the reduction of space charge with increasing lanthanum concentration. The presented changes in grain and grain boundary resistance, although determined for high temperatures, will allow for the extrapolation of the electrical properties of microstructural elements at room temperature, which will undoubtedly be helpful in designing materials for practical applications. The lanthanum dopant has a very positive effect not only on electrical properties but also improves the piezoelectric properties of lead-based perovskite materials. In the next stage of our research, we will focus on this aspect.  
The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app14219854/s1](https://www.mdpi.com/article/10.3390/app14219854/s1)]([https://www.mdpi.com/article/10.3390/app14219854/s1](https://www.mdpi.com/article/10.3390/app14219854/s1)): S1a,b and S2a,b: The frequency dependence of the (a) real and (b) imaginary components of the impedance of PBZT 25/70/30 ceramics modified with lanthanum ions; S3a,b and S4a,b: Dependence of the lnR\({}_{\rm G}\)(1/T) and lnR\({}_{\rm GB}\)(1/T) of PBZT 25/70/30 ceramics doped with lanthanum.  
Figure 9: (**a**) The natural logarithm of electric conductivity vs. inverse temperature for the undoped and La-modified PBZT 25/70/30 ceramics. (**b**) The activation energy of DC conductivity as a function of lanthanum dopant concentration.  
**Author Contributions:** Conceptualization, M.A.-H.; methodology, M.A.-H.; results analysis, J.A.B., B.W.-D., K.O., and T.P.; investigation, M.A.-H., B.W.-D., and J.A.B.; data curation, M.A.-H., J.M., and R.P.; writing--original draft preparation, M.A.-H. and J.M.; writing--review and editing, M.A.-H., J.M., and K.O.; visualization, T.P. and M.A.-H.; supervision, M.A.-H.; project administration, M.A.-H.; funding acquisition, M.A.-H. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research received no external funding.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Data are contained within the article.  
**Conflicts of Interest:** The authors declare no conflicts of interest.