Enhanced High-Temperature Piezoelectric Coefficients and Thermal Stability of Fe- and Mn-Substituted Na0.5Bi0.5TiO3 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 Na0.5Bi0.5TiO3 (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 degrees 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.