Abstract
The phase transition, microscopic morphology and optical and ferroelectric properties are studied in a series of La- and Co-doped KNbO3-based ceramics. The results show that the doping induces the transformation from the orthorhombic to the cubic phase of KNbO3, significantly reduces the optical bandgap and simultaneously evidently improves the leakage, with a slight weakening of ferroelectric polarization. Further analysis reveals that (i) the Co doping is responsible for the obvious reduction of the bandgap, whereas it is reversed for the La doping; (ii) the slight deterioration of ferroelectricity is due to the doping-induced remarkable extrinsic defect levels and intrinsic oxygen vacancies; and (iii) the La doping can optimize the defect levels and inhibit the leakage. This investigation should both provide novel insight for exploring the bandgap engineering and ferroelectric properties of KNbO3, and suggest its potential applications, e.g., photovoltaic and multifunctional materials.
Highlights
In the past several decades, ferroelectric materials have become important candidates for photovoltaic, random-access memory and optoelectronic devices due to their inherent spontaneous polarization [1,2,3,4,5,6]
KNO, like most ferroelectric materials, has a wide optical bandgap (Eg > 3 eV) and a low utilization rate of sunlight, and the problem of how to increase its absorption response to visible light has become a popular research direction for KNO materials [8], e.g., by doping or ion substitution or composition, which are effective methods to adjust the optical bandgap and electrical property, as representatively reported with Mn doping by Manikandan et al [9] and with
The large leakage current of pure KNO is a key issue, which should intrinsically hinder its application as perovskite ferroelectric materials [11,12]
Summary
In the past several decades, ferroelectric materials have become important candidates for photovoltaic, random-access memory and optoelectronic devices due to their inherent spontaneous polarization [1,2,3,4,5,6]. Co doping can significantly reduce the Eg and enhance the optical absorption response to visible light due to the generation of new electronic level states within the gap of KNO.
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