Crystal Structure, Phase Transitions and Photoferroelectric Properties of KNbO3-Based Lead-Free Ferroelectric Ceramics: A Brief Review

Abstract

Ferroelectric KNbO 3 (KN) ceramics were first fabricated in the 1950s, however, their use in commercial technical applications has been hampered by inherently challenging processing difficulties. In the early 1990s, the interest in KN ceramics was revived by the pursuit of Pb-free piezoceramics. More recently the search for inexpensive photovoltaic materials alternative to Si prompted bandgap engineering studies in KN-based solid solutions. If the ferroelectric and piezoelectric properties of KN-based ceramics are now well established, the understanding of chemical doping on the bandgap of KNbased ceramics is still in its infancy. Here we provide a brief review on the current understanding of the structure-property relationships in this class of materials, which successively covers crystal structures, structural phase transitions, lattice dynamics, polarization, solid solutions and bandgap engineering of KN.

Electroceramics for High-Energy Density Capacitors: Current Status and Future Perspectives

“…The electronic structure and band gaps of semiconductor can be studied theoretically using, e.g., linear discriminant analysis, or experimentally, e.g., absorbance spectroscopy and diffuse reflectance spectroscopy. 39 A general rule of thumb is that the activation energy ( E a ) for conduction is approximately half E g . Both may be increased by doping or through the formation of solid solutions, often delivering higher BDS and W rec .…”

X-ray diffraction study of the atomic interactions, anharmonic displacements and inner-crystal field in orthorhombic KNbO3

“…KNbO 3 (KNO) is a canonical example of a ferroelectric material with a perovskite structure, differing from other representatives of this family by the high values of the spontaneous polarization, piezoelectric and electro-optical coefficients (Lines & Glass, 2001;Shirane et al, 1954;Hewat, 1973;Wang et al, 2020). It is the only ferroelectric with the same set of phase transitions as BaTiO 3 , but with more noticeable structural distortions and enthalpy changes in the observed phase sequence.…”

“…The average and local atomic and electronic structure of potassium niobate, its optical and ferroelectric properties, the mechanism of phase transition and spontaneous polarization have been studied using a wide set of experimental and theoretical methods (Hewat, 1973;Wang et al, 2020;Yamanaka et al, 2009;Shuvaeva et al, 1998;Liang & Shao, 2019;Stash et al, 2017;Nakamoto et al, 2006;Bozinis & Hurrell, 1976;Kalinichev et al, 1993;Postnikov & Borstel, 1994;Cochran, 1969;Currat et al, 1989;Fu et al, 1999). The KNO electronic band structures and the densities of states (DOS) and their link to the mechanism of polarization have also been investigated (Fu et al, 1999;Schmidt et al, 2017).…”

“…To estimate the spontaneous polarization, both experimental and computational methods have been used, but the results obtained so far are not reliable, as discussed by Maksimov et al (2004). The magnitude of polarization in orthorhombic KNO, estimated by various experimental methods, is in the range 20-49 mC cm À2 (see, for example, Wang et al, 2020). Calculations by the Berry phase approach gave P s values ranging from 34 to 41 mC cm À2 (Fu et al, 1999;Wang et al, 2020;Yamanaka et al, 2009).…”

“…The magnitude of polarization in orthorhombic KNO, estimated by various experimental methods, is in the range 20-49 mC cm À2 (see, for example, Wang et al, 2020). Calculations by the Berry phase approach gave P s values ranging from 34 to 41 mC cm À2 (Fu et al, 1999;Wang et al, 2020;Yamanaka et al, 2009). The phonon model considers normal harmonic vibrations, while the displacements of atoms in a crystal occur in the position space.…”