Phase switching at low field and large sustainable strain output in domain engineered ferroic crystals

Fundamental shortcomings of ferroelectrics (FEs) are low induced strain and high electric field often required for practical application in actuation, sensors, and acoustics. Although domain engineered FE single crystals deliver an order of magnitude improvement, fatigue remains another drawback in achieving reliable multiple domain switching crucial for memory storage. We demonstrate that under specially compressive stresses FE relaxors exhibit low field induced reversible and sustainable strain associated with FE-FE phase switching and unusual and unexpected lack of fatigue after several millions cycles is believed due to strain accommodation occurring in ferroics. Polarized light microscopy and X-ray diffraction are in a very good agreement with macroscopic observation and phenomenological model confirming proposed transformational path. The phenomena presented in this work are envisioned to be universal in domain engineered ferroics enabling mechanical stress to be used for strain and polarization control of electromechanical energy conversion. Finkel et al. show that the ferroic morphotropic relaxor PIN-PMN-PT (i.e., the ternary lead indium niobate - lead magnesium niobate - lead titanate) crystal exhibits an unusual lack of fatigue after a million of strain cycles, compared to other ferroic systems degrading after a few cycles. A strain accommodation model is proposed as a plausible explanation to sustainable phase switching, supported by polarized light microscopy experiments under applied electric field. X-ray diffraction experiments on "free" and "clamped" crystals reveal a lattice strain that is in very good agreement with the macroscopic observation and phenomenological model calculation. The results confirm the proposed hypothesis of a phase transition from macro-domain ferroelectric rhombohedral (F_R) to mono-domain ferroelectric orthorhombic (F _O).