Investigation of structural and enhanced piezoelectric properties in low lead content Na0.5Bi0.5TiO3-BaTiO3-PbTiO3 system

Through this work the authors report the structural, ferroelectric, and piezoelectric properties of PbTiO ₃ modified ceramics: (1–2x)Na ₀. ₅Bi ₀. ₅TiO ₃-xBaTiO ₃-xPbTiO ₃ : (1–2x)NBT-xBT-xPT with x = 0.01, 0.03, 0.05, 0.07 and 0.09. The X-ray diffraction analysis of (1–2x)NBT-xBT-xPT revealed the existence of monoclinic (M) phase for x = 0.01 and 0.03 with the presence of ½(311) superlattice reflection, which acts as a structural bridge between the Rhombohedral (R) and Tetragonal (T) phases. Phase transition from M to T phase was observed at x = 0.03 which is supported by the presence of (002)/(200) splitting in the diffraction pattern. The measured mean grain size and density for x = 0.03 was 5.7 µm and 5.834 g/cm ³ respectively, which was the maximum compared to other compositions. The chemical state of elements in the ternary system is found out using the X-ray photoelectron spectroscopy. A diffuse phase transition is perceived from the temperature dependent dielectric studies for x ≤ 0.03, while this diffusiveness decreases for x > 0.03 with the increase in concentration of substituents. Besides, the ferroelectric (FE) to relaxor (RE) transition, T _FR is also diminished in higher concentration of BT and PT. A well saturated ferroelectric hysteresis loop with saturation polarization ( P _s) and remnant polarisation ( P _r) values of 35 and 32 µC/cm ² respectively is achieved for x = 0.03. Under an applied field of 48 kV/cm, a unipolar strain value of 0.26% is achieved for the same composition with a piezoelectric charge co-efficient ( d 33 * ) of 541 pm/V. The superior piezoelectric performance shown by (1–2x)NBT-xBT-xPT with a very low lead content of 3 mol%, which is at the proximity of M-T phase transition is explained using the polarisation rotation mechanism, that occurs in conjunction between polar-polar phases. The flat free energy profile that exists at the phase boundaries, eases the rotation of the polarisation vector and hence the piezoelectric constant. Also, a larger grain size will also relieve the polarisation rotation.