The giant strain response mechanism in textured Mn-modified 0.925(Bi0.5Na0.5)TiO3-0.075BaTiO3 relaxor ferroelectric ceramics

This work highlights structural and domain evolution, orbital hybridization, and giant strain in the textured [(Bi1/2Na1/2)0.925Ba0.075](Ti0.998Mn0.002)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.