Enhanced piezoelectricity in Na and Ce co-doped CaBi <sub>4</sub>Ti <sub>4</sub>O <sub>15</sub> ceramics for high-temperature applications
Zimeng Hu, Vladimı́r Koval, Hangfeng Zhang, Kan Chen, Yajun Yue, Dou Zhang, Haixue Yan
Abstract
The Na and Ce co-doped CaBi<sub>4</sub>Ti<sub>4</sub>O<sub>15</sub> (CBT)<sub> </sub>Aurivillius ceramics in a Ca<sub>1-<em>x</em></sub>(Na<sub>0.5</sub>Ce<sub>0.5</sub>)<em><sub>x</sub></em>Bi<sub>4</sub>Ti<sub>4</sub>O<sub>15</sub> (CNCBT, <em>x </em>= 0, 0.03, 0.05, 0.08 and 0.12) system were synthesized by the conventional solid-state sintering method. All compositions show a single-phase orthorhombic (space group <em>A</em>2<sub>1</sub><em>am</em>) structure at room temperature. The shift of the Curie point <em>T</em><sub>c</sub> towards lower temperatures on doping results from the increased tolerance factor<em> t</em>. The substitution-enhanced ferroelectric performance with large maximum polarization and facilitated domain switching is evidenced by the developed <em>P-E</em> and <em>I-E</em> hysteresis loops. The piezoelectric coefficient <em>d</em><sub>33</sub> (20.5 ± 0.1 pC/N) of the <em>x</em> = 0.12 sample is about four times larger than that of pure CBT. The improved piezoelectric properties can be attributed to the high remnant polarization and relatively high permittivity. In addition, multi-sized (micron and sub-micron) domain structures were observed in the CNCBT ceramics by piezoelectric response microscopy. The multiple sized ferroelectric domain structure with smaller domains is beneficial to the easy domain switching, enhanced ferroelectric performance and improved piezoelectric properties of the CNCBT ceramics. The designed Aurivillius-phase ferroelectric ceramics with the Curie point around 765 °C and high <em>d</em><sub>33</sub> are suitable for high-temperature piezoelectric applications.