Enhanced High‐Temperature Piezoelectric Coefficients and Thermal Stability of Fe‐ and Mn‐Substituted Na 0.5 Bi 0.5 TiO 3 Ceramics

Bismuth‐based ferroelectric ceramics are currently under intense investigation for their potential as Pb‐free alternatives to lead zirconate titanate‐based piezoelectrics. The present work evaluated the thermal depoling behavior of various compositions of Na 0.5 Bi 0.5 TiO 3 (NBT), one of the Bi‐based materials of broad interest, through in situ and ex situ measurements of the piezoelectric constant ( d 33 ). A range of ceramics was prepared by substituting 0.5–2 at.% of Fe or Mn for Ti. It was found that a low dopant concentration (0.5 at.%) increases the depolarization temperature ( T d ) with a minimal loss in room temperature d 33 , allowing for high piezoelectric coefficients at elevated temperatures. For example, 0.5 at.% Fe substitution leads to an enhanced piezoelectric coefficient of d 33 of 133 pm/V at an elevated temperature of 180°C. However, with further increase of dopant concentration, T d decreases in both Mn‐ and Fe‐doped NBT. The in situ depoling measurements of 0.5 at.% Fe‐ and Mn‐doped NBT in the present work exhibit the potential for higher temperature applications.