Coexisting ferroelectricity and photoconductivity in doped LN-type ZnSnO3 nanospikes

Abstract

Lead-free noncentrosymmetric (NCS), Lithium Niobate (LN)-type oxide, ZnSnO3, is an attractive candidate as emerging ferroelectric-photovoltaic solar absorber as it has well developed ferroelectricity and possibility of band-gap engineering. Here, simple solvo (hydro)thermal synthesis, ferroelectric (Ps ≈ 2.3 μC/cm2, and Pr ≈ 1.3 μC/cm2 at Ec = 40 kV/cm from undoped sample) and photoconductive properties of largely LN-type ZnSnO3 nanospikes (NSs) are studied and reported before and after doping with varying Ca and Ba molar concentration. A gradual shift in band gap from ∼4.15 eV in undoped sample is noticed by both kinds of doping (∼2.8 and ∼2.7 eV for 6 mol. % Ca and 4 mol. % Ba, respectively) and a consecutive strain in the lattice of ∼0.8–3% is estimated in the doped NSs. Furthermore, these optimized doped samples retain ferroelectricity (Ps ≈ 2.19 μC/cm2 for Ca doping and Ps ≈ 2.66 μC/cm2, for Ba doping at Ec ∼ 20 kV/cm, respectively), while conductivity in light appear (∼10 times for Ca doping and ∼3 times for Ba doping). The doped samples additionally show photo-switching behavior with a sharp rise and a decay in the ON-OFF cycle reaching a current of 10 nA in a little more than 1 min for optimized Ca doping. The observation of coexisitng ferroelectricity, and simultaneous photoconductivity in doped LN-type ZnSnO3 opens up further interest and possibility of exploring LN-type ferroelectric oxide nanostructures for photosensing and photovoltaic applications.