The giant strain response mechanism in textured Mn-modified 0.925(Bi_0.5Na_0.5)TiO₃-0.075BaTiO₃ relaxor ferroelectric ceramics

This work highlights structural and domain evolution, orbital hybridization, and giant strain in the textured [(Bi_1/2Na_1/2)_0.925Ba_0.075](Ti_0.998Mn_0.002)O₃ (BNT-7.5BT-0.2%Mn) ceramics. The as-sintered textured specimens reveal a predominant tetragonal P4bm (fraction∼94.4%) phase with a minor rhombohedral R3c (fraction∼1.4%) phase. X-ray absorption spectra indicate reduced hybridization between the O 2p and the Na 3sp/Bi 6sp/Ti 3d orbitals, implying decreased atomic bonding due to Mn doping. A mixture of Mn²⁺, Mn³⁺, and Mn⁴⁺ valence states was identified in the ceramic matrix. In-situ electric (E)-field dependent XRD results show a reversible E-field-induced phase transition, suggesting an ergodic relaxor ferroelectric. An E-field-induced giant strain of ∼0.495% at room temperature is attributed to the oriented relaxor ferroelectric P4bm phase and decreased bonding strength, which facilitate a transition from relaxor to ferroelectric phase. The poled specimen at E = 60 kV/cm shows a structural transition sequence of tetragonal P4bm + rhombohedral R3c →∼220°C tetragonal P4bm →∼483°C cubic.