Strain regulation via composition and valence dependent substitution in BNT-based solid solutions

Simultaneous composition and valence-dependent strain regulation is achieved in lead-free (Bi_0.5Na_0.4K_0.1)_1-2xSm_2xTi_1-xMn_xO₃ (BNKT-SM100x) ceramics by a facile co-doping design with Sm³⁺ and Mn²⁺. By simply controlling the sintering temperature, Mn ions exhibited mixed-oxidation states with different ion radius and electronic structures, further adjusting the crystalline field. The regulated disorder degree finally induced large electro-strain (0.445%) under appropriate doping contents (x ​= ​0.01) and sintering temperature (1150 ​°C). Moreover, the random effect of Mn²⁺ (arising from the different valence and radius comparing with Ti⁴⁺) is stronger than the pinning effect due to the suppressed oxygen vacancies, and the different crystal structures may also affect the role of Mn²⁺. The domain morphologies with mixed nanodomain and ferroelectric domain were observed in the BNKT-SM1 ceramics, further demonstrating the coexistence of random effect and pinning effect. It is believed that the self-strain regulation phenomenon in this work may serve as an effective strategy for designing ferroelectrics with high strain performance.