Unveiling the dynamics of phase-transition from ferroelectric to relaxor behavior in Nd-doped BNT-based lead-free piezoelectric ceramics

Abstract

In this study, lead-free 0.852Bi_0.5Na_0.5TiO₃−0.12Bi_0.5K_0.5TiO₃−0.028BaTiO₃ (BNKBT 85.2/12/2.8) ceramics were synthesized using the conventional mixed oxide method, with Nd³⁺ doping at concentrations of 0.00, 0.25, 0.50, 0.75, 1.00, and 2.00 mol%. The research focused on the phase transition from ferroelectric to relaxor and the associated electromechanical properties. X-ray diffraction (XRD) analysis confirmed the successful incorporation of Nd³⁺ into the lattice, forming a perovskite phase and indicating the coexistence of multiple phases in the morphotropic phase boundary (MPB) region. The transition from ferroelectric to relaxor was observed in the polarization–electric field (P–E) and strain–electric field (S–E) loops. Pure samples exhibited ferroelectric behavior, with a relatively square P–E loop and a butterfly-shaped S–E loop. At 0.5 mol% Nd³⁺, a pinched P–E loop and a significant negative strain in the S–E loop were observed. At 2.0 mol% Nd³⁺, the ceramics demonstrated relaxor characteristics, with a thin P–E loop and minimal negative strain in the S–E loop. The optimal piezoelectric coefficient (d₃₃), remnant polarization (P_r), and dielectric constant (ε_r) were found at 0.5 mol% Nd³⁺, reaching 243 pC N⁻¹, 36.61 μC cm⁻², and 1814.54, respectively. The highest value of 761 pm V⁻¹ was observed at 2.0 mol% Nd³⁺, indicating dominant relaxor behavior. This study highlights the significant influence of Nd³⁺ doping on the phase transition and electromechanical properties of BNKBT ceramics, underscoring their potential as lead-free alternatives for sensor and actuator applications.