## 5 Conclusions  
Two novel methods were proposed which allowed the stabilization of the \(\delta\)-Bi\({}_{2}\)O\({}_{3}\) type phase at room temperature (up to about 575 \({}^{\circ}\)C) in the form of nanocrystalline glass-ceramics. The first one is based on the fast quenching of melted \(\alpha\)-Bi\({}_{2}\)O\({}_{3}\) phase using the twin rollers technique. The second one is based on the free cooling of that melt. In both methods, ceramic crucibles were used, whose compositions contained glass forming SiO\({}_{2}\) and Al\({}_{2}\)O\({}_{3}\) oxides. Diffusion of these oxides into the melted sample was a key step during the synthesis of \(\delta\)-Bi\({}_{2}\)O\({}_{3}\) based glass-ceramics. Prepared nanocomposites exhibit fairly good conductivity of oxygen ions at 500 \({}^{\circ}\)C. Our studies on the preparation of \(\delta\)-Bi\({}_{2}\)O\({}_{3}\) based glass-ceramics in the PtIr crucible with controlled SiO\({}_{2}\) and Al\({}_{2}\)O\({}_{3}\) dopants are underway.  
Conceptualization, J.E.G.; methodology, P.K.-F.; validation, J.E.G. and P.K.-F.; formal analysis, P.K.-F.; investigation, P.K.-F.; resources, J.E.G. and P.K.-F.; writing--original draft preparation, P.K.-F. and J.E.G.; visualization, P.K.-F.; supervision, J.E.G.; project administration, P.K.-F.; funding acquisition, P.K.-F. and J.E.G. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Science Center, Poland, Grant Preludium-14 no. 2017/27/N/ST5/01943.  
Not applicable.  
The data presented in this study are available in Studies on \(\delta\)-Bi\({}_{2}\)O\({}_{3}\) based glass-ceramics stabilized by novel methods based on nanocrystalline of glasses (contained within the article).  
**Acknowledgments:** The authors are grateful to [PERSON] for his valuable ideas that assisted in the design of the present study, and to [PERSON] for his technological guidance in preparing samples for the IS measurements and assistance with the SEM analysis and imaging. The authors would also like to extend their thanks to the Institute of High Pressure Physics of the Polish Academy of Sciences for the SEM micrographs and EDX analysis.  
**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.  
Appendix A Preparation of the samples for IS measurements. The samples were initially crushed in a mortar and then ground in a planetary ball mill for 2 h at 240 RPM to homogenize the grains. In the next step, pellets were formed and compressed in a uniaxial press at 12 MPa for 2 min and 8 MPa for another 10 min, followed by sintering in a chamber furnace at 100-150 \({}^{\circ}\)C for 12 h to harden the sample. The lack of effect of the presented preparation on the crystalline phase of the samples was confirmed by an XRD study. In the last step, platinum electrodes were sputtered onto the pellets under high vacuum conditions. To ensure good surface contact with the electrodes, the samples were previously ground.  
Appendix B Thermal evolution of XRD patterns of the materials synthesized under different conditions.