**4. Conclusions**

Gd/Mn co-doped CaBi4Ti4O<sup>15</sup> (CBT-*x*Gd/0.2Mn, *x* = 0, 0.02, 0.06, 0.08, 0.11) ceramics were synthesized by the solid-state reaction method. The structures, electrical conduction, and dielectric relaxation behaviors of CBT-*x*Gd/0.2Mn ceramics were studied. Some main results were obtained as follows:


**Author Contributions:** D.W. performed the experiment; H.Z. analyzed the experimental data; L.L. contributed reagents/materials/analysis tools; D.W. wrote the paper; Y.C. conceived and designed the experiment. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by the State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and astronautics (Grant No. MCMS-E-0522G01), the State Key Laboratory of Crystal Materials, Shandong University (Grant No. KF21-08), and the Guangdong Provincial Key Laboratory of Materials and Technologies for Energy Conversion (Grant No. MATEC2022KF001).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
