Structural and optical properties of KNN nanocubes synthesized by a green route using gelatin

Abstract

Sodium potassium niobate nanoparticles [( K 0.5 Na 0.5) NbO 3, KNN ], KNN-NPs, were synthesized using a modified sol–gel method. Structural and optical properties of the prepared samples were investigated by thermogravometric analyzer (TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman and UV–Vis spectroscopy. The XRD patterns showed that the formation of the orthorhombic KNN-NPs starts at 500°C calcination temperature. Raman spectroscopy was used to investigate the crystalline symmetry and the structural deformation of the prepared KNN-NPs. TEM images showed that the morphology of the prepared particles is cubic, with the average size of about 50 nm. From diffused reflectance spectroscopy along with using Kubelka–Munk method, the energy bandgaps were determined to be indirect with the values of 3.13 eV and 3.19 eV for the samples calcined at 500°C and 600°C, respectively.

Lattice parameters and electronic bandgap of orthorhombic potassium sodium niobate K$$_{0.5}$$Na$$_{0.5}$$NbO$$_{3}$$ from density-functional theory

“…[14]. Although the electronic and optical bandgaps are distinct physical quantities, our results are in good quantitative agreement with the available experimental data [35][36][37][38][39][40] if we take the quasiparticle corrections to the DFT eigenvalues and the exciton binding energy [27] into account.…”

“…In each case, the fundamental (indirect) bandgap equals the energy difference between [14] and by Yang et al [15] at the same level of theory but with different exchange-correlation functionals. The observable optical bandgap, obtained by adding the quasiparticle correction of 1.64 eV and subtracting the exciton binding energy of 0.5 eV [27], is in good quantitative agreement with experimental measurements at x = 0 [35][36][37][38][39] and x = 0.5 [37,40] the Kohn-Sham eigenvalues of the highest valence-band and the lowest conduction-band state within DFT. Our results reveal that the bandgap is very similar for all six configurations of KNN50, which is plausible from the fact that the alkali-metal atoms do not contribute to the density of states near the band edges [22].…”

“…Hence, it seems natural to use r = 2 also for orthorhombic KNN50. The values of 3.15 eV [37] and 3.19 eV [40] derived in this way are essentially identical to those of KNbO 3 and confirm that the optical bandgap does not depend strongly on x. In particular, Khorrami et al [37], who analyzed samples with x = 0 and x = 0.5 using the same fabrication and measurement techniques, obtained nearly identical gaps of 3.18 eV and 3.15 eV, respectively.…”

“…It should be noted that an extrapolation with r = 1/2 leads to substantially larger values for the optical bandgap if based on the same experimental data for the absorption coefficient [39,40]. As a consequence, several experimental studies that falsely assumed a direct instead of an indirect transition between the valence and the conduction bands reported much larger optical bandgaps for KNbO 3 [41] and KNN50 [42,43] than the ones featured in Fig.…”

Comprehensive biocompatibility of nontoxic and high-output flexible energy harvester using lead-free piezoceramic thin film

“…2(a)). In contrast to sapphire, the L-KNN film absorbs the incident energy since the KNN-based ceramic band-gap energy is lower than the laser photonic energy, 59,60 and this results in meltingdissociation of L-KNN at the interface, followed by the transfer of the L-KNN film from sapphire to the pre-attached flexible plastics (the right panel of Fig. 2(c)).…”