Chemical nature of giant strain in Mn-doped 0.94(Na0.5Bi0.5)TiO3–0.06BaTiO3 lead-free ferroelectric single crystals

Giant bipolar and unipolar strains i.e. Smax > 0.5%, εmax/Emax > 1000 pm V–1 have been observed in Mn-doped Na0.5Bi0.5TiO3–6BaTiO3 single crystals after being annealed. Temperature-dependent impedance spectra were studied and activation energies of oxygen vacancies were calculated accordingly. The two different binding energies present in X-ray photoelectron spectra for Na and Bi were assigned to different coordinate environments. However, titanium exhibits only one oxidation state (e.g. Ti4+). The site occupation and valence fluctuation of Mn were characterized by electric paramagnetic resonance spectra.