Size dependence of the polarization and dielectric properties of KNbO₃ nanoparticles

Abstract

Ferroelectric nanostructures have recently attracted much attention due to the continuous demand of miniaturizing devices and discovering novel phenomena. Therefore, in depth study of the ferroelectric, and dielectric properties at various particle sizes in nanoscale ferroelectrics is of technological importance. Unfortunately, research aimed at discovering and understanding the size effect on the electric properties of ferroelectric nanostructures are scarce. Here, we investigate the spontaneous polarization and dielectric constant at various sizes of nanocrystalline potassium niobates (KNbO 3 ) by using powder X-ray diffraction (XRD) Rietveld refinement, Raman spectroscopy, and theoretical calculation. It is surprising to find that the spontaneous polarization P s reaches the highest value of 40.3 mC cm À2 at 100 nm, and decreases with increasing grain size from 100 nm to 500 nm. The dependence of the dielectric constant on the grain size shows similar variation as that of spontaneous polarization. It is deduced that the large lattice distortion induced by lowering the grain size facilitates the increase of P s , which in turn contributes mainly to the enhancement of the dielectric constant.

Electrically Insulating Plasma Polymer/ZnO Composite Films

“…It can be understood that the dielectric constant of smaller-sized nanoparticles exhibited a higher value, whereas, with an increase in particle size, the dielectric constant decreased. This is in agreement with previous findings [19]. In contrast, other studies reported that the dielectric constant increases with an increase in the size of nanoparticles [20].…”

“…In order to theoretically estimate the contribution of the dielectric constant of pure ZnO nanoparticles to that of the composite, we used the modified Rother–Lichtenecker equation. The measured dielectric constant is given by the relation [19]: ε measured = exp [ln ε 1 + f 2 (1 − k ) ln ( ε 2 / ε 1 )] where ε measured , ε 1 , and ε 2 represent the dielectric constant of the ZnO/Ge composite, the polymer medium, and the ZnO nanoparticle, respectively, f 2 represents the volume fraction of the ZnO nanoparticle, and k is the shape dependent factor ( k = 0.5).…”

Phase transition and piezoelectric properties of alkali niobate ceramics through composition tuning

“…Larger grain is in favor of piezoelectric properties enhancement because the motion of domain wall can be released more compared with small grain. [30][31][32] On the other hand, too much larger grains can deteriorate piezoelectric properties inversely, because of much more bubbles are generated during the process of grain excessively growing, and therefore the densication of the ceramics reduces. Transition temperature of ferroelectric-paraferroelectric phase (T C ) for x ¼ 0.02, 0.035, 0.045, 0.06 is also observed in Fig.…”

Electrocaloric response of KNbO3 from a first-principles effective Hamiltonian

“…Birol et al [24] reported measuring a spontaneous polarization of 25 C cm −2 in polycrystalline KNbO 3 . Ge et al [25] studied the impact of crystal size on the polarization in KNbO 3 and found a spontaneous polarization of 40.3 C cm −2 . Kleemann et al [26] reported a spontaneous polarization of 37 C cm −2 .…”