Dielectric and electromechanical properties of barium and zirconium co-doped sodium bismuth titanate

Abstract

Compositional exploration was conducted within the alkaline bismuth titanate system by doping on the A- and B- sites with Ba⁺² and Zr⁺⁴, respectively. Results on the phase, dielectric and electromechanical properties of single crystals and polycrystals for this new family of relaxor perovskite ferroelectrics are presented. The actuation and polarization characteristics in this system were found to be highly sensitive (within 2 mol%) to cation doping levels, and tailored compositions successfully isolated predominantly electrostrictive actuation at room temperature. Ultra-high room temperature electrostriction was observed in co-doped (Ba + Zr) NBT polycrystals (NBT-14BT-4NBZ) and <100> single crystals (NBT-12BT-4NBZ), up to 0.24% and 0.45% strain, respectively, with negligible hysteresis at 0.05 Hz. Polycrystals with d₃₃ of up to 780 pC/N and single crystals with d₃₃ up to 2000 pC/N were measured. The low frequency actuation properties in the NBT-BT-NBZ compositions surpass highest reported values of strain and d₃₃ for polycrystalline PMN and PLZT and single crystal PMN conventional lead electrostrictors. Predominantly ferroelectric room temperature unipolar actuation in polycrystalline NBT-14BT-3NBZ at 0.05 Hz was observed to be linear and non-hysteretic, reaching up to 0.14% strain and d₃₃ of 310 pC/N at 60 kV/cm. These low frequency properties match the reported strain and d₃₃ values for conventional PZT-8, PMNT, and PZT-5a hard ferroelectrics and are more than double the reported values for polycrystalline NBT-BT (d₃₃ = 125 pC/N). Electrostrictive and ferroelectric compositions in the NBT-BT-NBZ system show the highest actuation strain and d₃₃ reported to date in any polycrystalline, lead-free composition.