Effect of Bismuth Doping on the Dielectric and Piezoelectric Properties of Ba_1-xBi_xTiO₃Lead-Free Ceramics

Abstract

In this paper we report the dielectric and piezoelectric properties of Bi modified Ba_1-xBi_xTiO₃ lead-free ceramics. These ceramic samples were synthesized by conventional solid state reaction method. The XRD spectra recorded at room temperature (RT) suggested decrease in the tetragonality (c/a) for Bi doped derivatives with the presence of minor rhombohedral phase for heavily doped specimens. The grain boundary pinning occurring in slightly Bi-doped derivative (x = 0.025) was found to reduce the grain size to submicron regime. However, for higher Bi doping the presence of liquid phase led to the grain coarsening. The doped derivatives exhibited shifting of the paraelectric-ferroelectric (PE-FE) phase transition towards RT with rather diffused Curie peak. The substitution of Bi³⁺ (with different ionic radii and electronegativity) on A-site of ABO₃ structure resulted in regions with modified polar structure giving rise to diffused PE-FE phase transition. The specimen with x = 0.025 exhibited enhanced planar electro-mechanical coupling constant (k_p) ∼ 25% with longitudinal piezoelectric constant (d₃₃) of ∼112 pC/N. The sample with x = 0.025 also exhibited 0.085% electric-field induced strain along with the remnant polarization (2P_r) of ∼15 μC/cm² and coercive field (2E_c) of ∼22 kV/cm. The increased E_c with reasonable P_r is an important material characteristics for the stable functionality of the memory devices.

Keywords:

• Lead-free
• piezoelectric
• ceramics
• barium titanate
• doping