BNT‐based ferroelectric ceramics: Electrical properties modification by Ta 2 O 5 oxide addition

Due to their superior piezo‐responses (strain S  > 0.3%), bismuth sodium titanate (BNT)‐based relaxor ferroelectrics have received much attention. Compared to other chemical elements, tantalum (Ta) doping provides superior electro‐strain for these ferroelectrics, while the effect of Ta 2 O 5 as oxide additive has been rarely reported. Herein, lead‐free piezoceramics of Bi 0.5 (Na 0.72 K 0.22 Li 0.06 ) 0.5 TiO 3 ‐ x Ta 2 O 5 (BNKLT‐ x Ta 2 O 5 , x  = 0‐0.015) are synthesized. We study the effects of Ta 2 O 5 addition on the crystal structure, piezoelectric responses, dielectric properties, and ferroelectric properties of BNKLT ceramics. All of the ceramics exhibit a typical perovskite structure, and Ta 2 O 5 diffuses into the BNKLT lattice to form a uniform solid solution. The addition of Ta 2 O 5 can make the grains more regular and uniform, while excess Ta 2 O 5 result in finer grains. The undoped BNKLT ceramics show good ferroelectric and piezoelectric properties (remnant polarization P r  = 22.5 μC/cm 2 and piezoelectric coefficient d 33  = 250 pC/N); however, the addition of Ta 2 O 5 leads to an clear degradation in d 33 and P r . Meanwhile, the addition of an appropriate Ta 2 O 5 amount leads to an increase in the electro‐strain, and the unipolar strain reaches 0.385% under 60 kV/cm for x  = 0.003, together with a higher normalized strain ( d 33 * = S max / E max ) of 633 pm/V ( x  = 0.003). The enhanced strain behaviors can be attributed to the coexistence of the ferroelectric and relaxor states, and an excellent electrostriction coefficient Q 33 ( Q 33  =  S / P 2 ) value of 0.038 m 4 C −2 is obtained under 60 kV/cm for x  = 0.003.