**4. Conclusions**

temperature.

**4. Conclusions**  An Aurivillius phase ceramic with a formula of Bi2.8Gd0.2TiNbO9 + 0.2 wt% Cr2O3 (abbreviated as BGTN−0.2Cr) was prepared by the conventional solid−state reaction route. Both the microstructures and electrical conduction behaviors of the BGTN−0.2Cr ceramic were studied. The BGTN−0.2Cr ceramic was crystallized in a pure Bi3TiNbO9 phase and composed of plate-like grains. Its ac conduction behavior could be explained by the Funke's jumping relaxation model. The maximum barrier height *WM*, hopping conduction activation energy *Ep*, and dc conduction activation energy *Ec* were determined to have values of 0.63 eV, 1.09 eV, and 0.73 eV, respectively. Impedance analysis in combination with modulus calculation revealed that grains provided a larger contribution to the conductance at high temperature and that *β* grew larger as temperature rose. The values of the activation energy (~1 eV) calculated from both *Z″* and *M*'' peaks suggested the electrical relaxation process to be dominated by the thermal activation of oxygen vacancies as defect charge carriers. Moreover, the BGTN−0.2Cr ceramic had a high *d*33 of 18 pC/N as well as a high *σ*dc of 1.52 × 105 Ω cm (600 °C). Such excellent electrical properties An Aurivillius phase ceramic with a formula of Bi2.8Gd0.2TiNbO<sup>9</sup> + 0.2 wt% Cr2O<sup>3</sup> (abbreviated as BGTN−0.2Cr) was prepared by the conventional solid−state reaction route. Both the microstructures and electrical conduction behaviors of the BGTN−0.2Cr ceramic were studied. The BGTN−0.2Cr ceramic was crystallized in a pure Bi3TiNbO<sup>9</sup> phase and composed of plate-like grains. Its ac conduction behavior could be explained by the Funke's jumping relaxation model. The maximum barrier height *WM*, hopping conduction activation energy *Ep*, and dc conduction activation energy *E<sup>c</sup>* were determined to have values of 0.63 eV, 1.09 eV, and 0.73 eV, respectively. Impedance analysis in combination with modulus calculation revealed that grains provided a larger contribution to the conductance at high temperature and that *β* grew larger as temperature rose. The values of the activation energy (~1 eV) calculated from both *Z* 00 and *M*00 peaks suggested the electrical relaxation process to be dominated by the thermal activation of oxygen vacancies as defect charge carriers. Moreover, the BGTN−0.2Cr ceramic had a high *d*<sup>33</sup> of 18 pC/N as well as a high *<sup>σ</sup>dc* of 1.52 <sup>×</sup> <sup>10</sup><sup>5</sup> <sup>Ω</sup> cm (600 ◦C). Such excellent electrical properties made it a competitive candidate for high−temperature piezoelectric materials.

made it a competitive candidate for high−temperature piezoelectric materials. **Author Contributions:** H.Z. conceived and designed the experiments; S.W. and D.W. performed the experiments; H.Z. analyzed the data; Q.C. contributed reagents/materials/analysis tools; H.Z. wrote the paper; Y.C. revised the paper. All authors have read and agreed to the published version **Author Contributions:** H.Z. conceived and designed the experiments; S.W. and D.W. performed the experiments; H.Z. analyzed the data; Q.C. contributed reagents/materials/analysis tools; H.Z. wrote the paper; Y.C. revised the paper. All authors have read and agreed to the published version of the manuscript.

of the manuscript. **Funding:** This work was supported by Applied Basic Research of Sichuan Province (No.2020YJ0317), the Open project from the Fujian Key Laboratory of Special Advanced Materials **Funding:** This work was supported by Applied Basic Research of Sichuan Province (No. 2020YJ0317), the Open project from the Fujian Key Laboratory of Special Advanced Materials (Development of Bi3TiNbO<sup>9</sup> High-temperature Piezoceramics, 2021), and the Open project from the Key Laboratory of Deep Earth Science and Engineering, Ministry of Education (DESE202007).

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

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.

**Acknowledgments:** The authors give thanks for SEM characterization technical support provided by the Institute of Advanced Study at Chengdu University.

**Conflicts of Interest:** The authors declare no conflict of interest. The authors alone were responsible for the content and writing of this article.
