Frequency-dependent ferro-antiferro phase transition and internal bias field influenced piezoelectric response of donor and acceptor doped bismuth sodium titanate ceramics.

The influence of donor (L a 3 +) and acceptor (S c 3 +) dopant on structural and electrical properties of lead-free B i 0.5 N a 0.5 Ti O 3 (BNT) ceramics system was investigated. Both donor and acceptor substitutions induced a structural transformation of pure BNT ceramics from a rhombohedral to a pseudocubic structure. Splitting of the (111) p c peak in pure BNT was considered symmetry identification for a rhombohedral structure. A micrometer level grain size (1.70 μm–2.81 μm), dense microstructure with good ferroelectric and piezoelectric performance (d 33 = 56 − 45 pC / N) was obtained. The 3% La content BNT ceramic shows an improved dielectric property. The Curie temperature increases from 355 °C for pure BNT to 365 °C for donor-doped and 370 °C for acceptor-doped BNT. The donor doping created cationic vacancies; acceptor doping induces oxygen vacancies that stabilized the polarization level. Maximum remnant polarization (P r) value has been obtained for 3% La-doped (P r = 27 μ C / c m 2) and 5% Sc-doped (P r = 20 μ C / c m 2) BNT system. Bipolar strain increased with the increase in donor dopant concentration resulting in a large electrostrictive coefficient (Q11 ∼ 0.0122%–0.045%) has been obtained. Electric field-induced unipolar strain value was enhanced to its maximum value (Smax = 0.14%) for 3% La content with normalized strain d 33 ∗ = 209 pm / V and Smax = 0.13% for 5% Sc with normalized strain d 33 ∗ = 155 pm / V at an applied electric field of 70 kV/cm and 50 kV/cm, respectively. The enhanced strain was considered to be associated with low internal bias field and maximum polarization level. In terms of capacitive response, 5% Sc holds a maximum current (∼0.017 mA) during polarization switching. [ABSTRACT FROM AUTHOR]