Effects of Na Excess on the Crystal Structure Ferroelectric and Piezoelectric Properties of (Bi_0.487Na_0.427K_0.06Ba_0.026)TiO₃ Lead-Free Piezoceramics

Abstract

In this research, (Bi_0.487Na_0.427K_0.06Ba_0.026)TiO₃ ceramics were prepared by conventional solid-state mixed-oxide method to incorporate Na excess according to the chemical formula (Bi_0.487Na_0.427+xK_0.06Ba_0.026)TiO₃, where x = 0.0, 0.005, 0.010, 0.015 and 0.020. The crystal structure, dielectric, ferroelectric and piezoelectric properties were systematically investigated with respect to the amount of Na excess. X-ray diffraction data identified pure perovskite structure for all compositions. The pseudocubic structure was observed for x = 0.0 − 0.005 before it transformed to rhombohedral structure at x ≥ 0.015. The grain size tended to be larger with increasing Na excess amount. Increasing x also led to a substantial increase in ferroelectric-relaxor transition temperature (T_F-R) from 80 °C (x = 0) to 110 °C (x = 0.020). With increasing x from 0 to 0.020, the standard polarization-electric field (P-E) hysteresis measurements revealed a reduction in remanent polarization (P_r) together with an increase in coercive field (E_c), which was further confirmed by the remanent P-E hysteresis measurements. In addition, the piezoelectric constant (d₃₃) was also found to steadily decrease as x increased. The observation of increased T_F-R and E_c along with a decrease in d₃₃ and P_r indicated a stabilization of ferroelectric order induced by Na excess. This research highlights the importance of sufficient control over A-site stoichiometry and how it affects the ferroelectric and piezoelectric properties of BNT-based ceramics.

Keywords:

• Lead-free BNT-BKT-BT ceramics
• Na-excess
• A-site nonstoichiometry
• Ferroelectric properties
• Piezoelectric properties

Acknowledgments

This work received financial support from the National Science, Research, and Innovation Fund (NSRF) through Naresuan University (Grant No. R2565B059). The authors would like to extend their gratitude to Prof. Dr. Gobwute Rujijanakul for providing facility support with the ferroelectric test system at Electroceramics research laboratory, Department of Physics and Materials Science, Faculty of Science, Chiang Mai University. Additionally, special thanks are given to Dr. Nitish Kumar for his invaluable assistance in proofreading and grammar check the manuscript.

Disclosure Statement

No potential conflict of interest was reported by the author(s).