Lead-free (Bi1/2Na1/2)TiO3 (BNT)-based incipient piezoelectrics are highly promising for high strain actuators, but the high electric fields (4 ~ 6 kV/mm) required for activation limit practical device integration. In the current literature, large strains are frequently attributed to local structural variations like microscopic core-shell architectures. This work systematically investigates an alternative pathway by introducing A-site Strontium (Sr) excess non-stoichiometry into 0.74(Bi1/2Na1/2)TiO3‒0.26SrTiO3 (BNST26) ceramics. Microstructural and X-ray diffraction analyses reveal highly dense, uniform matrices completely devoid of micro-scale core-shell boundaries or macroscopic symmetry distortions, revealing that Sr non-stoichiometry diverges from typical Bi-excess mechanisms. Interestingly, despite negligible variations in overall macro-scale strain behavior across the composition series, a peak normalized strain (Smax/Emax) of approximately 804 pm/V is achieved at a low driving field of 2 kV/mm for the 1 mol% Sr-excess specimen (x = 0.010). These results indicate that while Sr non-stoichiometry weakly influences nanoscale stability, it can be inferred that subtle modifications of local defect configurations optimize switching energy barriers, enabling high-strain, low-drive-field performance in lead-free relaxors.
Lead-free bismuth sodium titanate (BNT)-based ceramics have attracted strong attention as environmentally benign dielectric materials for high-efficiency electrostatic energy-storage capacitors. A key challenge is that pristine BNT typically exhibits large hysteresis, high remnant polarization, and limited dielectric reliability, which restrict recoverable energy storage and efficiency under practical electric fields. Here, we present a focused mini-review of recent studies to clarify how composition design, phase boundary tuning, defect chemistry, and microstructural control collectively enable slim or pinched polarization-electric field (P-E) behavior and improved energy-storage functionality in BNT-related bulk ceramics. The reviewed outcomes consistently show that stabilizing relaxor states governed by polar nanoregions (PNRs), often via solid-solution engineering and secondary relaxor/antiferroelectric-like incorporation, suppresses irreversible switching and reduces hysteresis loss, while densification and grain-size control enhance electrical homogeneity and breakdown strength. In addition, defect-mediated tuning of oxygen vacancy-related complexes is highlighted as an independent lever to control relaxor ergodicity and polarization reversibility, providing a complementary route to slim-loop optimization. These insights are expected to guide integrated design strategies that couple phase/relaxor-state engineering with defect and microstructure optimization, accelerating the development of reliable, temperature-robust, lead-free dielectric capacitors based on BNT-related ceramics.
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Progress and outlook of dielectric energy storage characteristics of Lead–free (K,Na)NbO3 based bulk ceramics/composite films for capacitors Twinkle, Varun Kamboj, Chetna, Arun Kumar Singh, Gurpreet Singh, Sanjeev Kumar Current Opinion in Solid State and Materials Science.2026; 44: 101297. CrossRef
Structural Stability and Electromechanical Response of Lead-Free (Bi1/2Na1/2)TiO3‒SrTiO3 Ceramics Under A-Site Strontium Non-Stoichiometry Yubin Kang, Trang An Duong, Gwang-Hwi Jeong, Chang Won Ahn, Yong-Jai Kwon, Hyoung-Su Han Journal of Electrical and Electronic Materials.2026; 39(5): 549. CrossRef
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