Experimental evidence of electronic polarization in a family of photo-ferroelectrics

Abstract

We report a family of ferroelectric materials which exhibit optical control of dielectric constant, polarization, and conductivity at ambient conditions. The evolution of photo-induced charge carriers under illumination of weak monochromatic light of wavelength λ = 405 nm developed electronic polarization that reorients or enhances the ionic polarization in the direction of the applied electric field, hence significantly increasing the net polarization. The presence of electronic polarization in perovskites, especially ABO₃ oxides, and the contribution to the ionic polarization, is a matter of debate among ferroelectric community; however, recent experimental evidence proved that electronic polarization contributes to overall polarization in different ways: if it is additive, it will act along the direction of ionic polarization; and if it is subtractive, it will act in the opposite direction. We report a newly developed lead-based ferroelectric family Pb_1−x(Li_0.5Bi_0.5)_x(Zr_0.2Ti_0.8)O₃ (PLBZT) for x = 0.3, 0.4, 0.5, which have been successfully synthesized by a conventional solid state reaction route. The X-ray diffraction patterns were recorded at room temperature and refined with Rietveld parameters which confirm its tetragonal structure with P4mm space group symmetry. The Raman spectra, dielectric properties and leakage currents are analyzed. The current conduction mechanisms obey bulk limited Poole–Frenkel model and provide optical dielectric constant similar to theoretical value to lead zirconate titanate.