Strategic B-site doping in BiFeO₃: A DFT-driven approach for enhanced piezoelectric performance

Piezoelectric materials, particularly bismuth ferrite (BFO) and its doped variants, are pivotal for advanced electronic and sensing applications due to their multifunctional properties. This study employs Density Functional Theory (DFT) calculations to systematically investigate the structural, electronic, elastic, and piezoelectric properties of undoped Fe₂O₃ and BiFeO₃, alongside their transition metal (Mn, Mo, Ni) and lanthanide (La, Ce, Sm) doped derivatives. Doping significantly enhances piezoelectric performance, with Mo-doped BiFeO₃ (MoBiFe₂O₆) exhibiting a high longitudinal piezoelectric coefficient (d₃₃ = 67.97 pC/N) and Sm-doped BiFeO₃ (SmBiFe₂O₆) showing a remarkable piezoelectric stress constant (e₃₃ = 8.25C/m²). Co-doping Mo and Sm (MoSmBiFe₃O₉) further amplifies these effects, achieving the highest values of d₃₃ = 103.45 pC/N, e₃₃ = 13.25C/m², a widened band gap (2.97 eV), and reduced elastic stiffness (C₁₁ = 84.23 GPa), indicating superior electromechanical coupling. Frequency-dependent analyses reveal enhanced dielectric permittivity (ε’ ≈ 165 at low frequencies). These results demonstrate that targeted doping, particularly with Mo and Sm, effectively tunes the functional properties of BFO, making it a promising candidate for high-performance piezoelectric devices.