Structural and microstructural description of relaxor-ferroelectric transition in quenched Na_(1/2)Bi_(1/2)TiO_(3)-BaTiO_(3)

Quenching lead-free Na_(1/2)Bi_(1/2)TiO_(3)-based ceramics from sintering temperature is established to increasethe depolarization temperature,Td and the lattice distortion.In situ synchrotron X-ray diffractionmeasurements were carried out on furnace cooled and quenched Na_(1/2)Bi_(1/2)TiO_(3)-BaTiO_(3)(NBT-BT)with 6and 9 mol.%BT to discern the field-induced ferroelectric order.Phase fractions were determined fromfull pattern Rietveld refinements and utilized together with the change in unit cell volume to calculatevolumetric strain resulting from phase transformations.NBT-6BT demonstrates a cubic symmetry in thefurnace cooled state but quenching stabilizes the rhombohedral R3c phase and delays the formation of afield-induced,long range-ordered tetragonal phase,thereby shifting the onset of macroscopic strain tohigher fields.A field-induced phase transition from a weakly distorted rhombohedral to tetragonal phasecan be observed in furnace cooled NBT-9BT.However,this phase transition cannot be detected inquenched NBT-9BT,since the ferroelectric tetragonal P4mm phase is stabilized in the initial state.Incontrast to the furnace cooled materials,both the quenched compositions exhibit overall negligiblevolumetric strain as a function of electric field.Furthermore,scanning electron micrographs of chemi-cally etched,poled and unpoled samples reveal an increased lamellar domain contrast in the quenchedmaterials.All these findings strengthen the hypothesis of a stabilized ferroelectric order resulting in theabsence of a field-induced phase transformation in quenched NBT-BT.