Synthesis and nonlinear optical properties of single-crystalline KNb3O8 nanowires

Vibrational Analysis of Paraelectric–Ferroelectric Transition of LiNbO3: An Ab-Initio Quantum Mechanical Treatment

The phase transitions between paraelectric (PE) and ferroelectric (FE) isomorph phases of LiNbO3 have been investigated quantum mechanically by using a Gaussian-type basis set, the B3LYP hybrid functional and the CRYSTAL17 code. The structural, electronic and vibrational properties of the two phases are analyzed. The vibrational frequencies evaluated at the Γ point indicate that the paraelectric phase is unstable, with a complex saddle point with four negative eigenvalues. The energy scan of the A2u mode at −215 cm−1 (i215) shows a dumbbell potential with two symmetric minima. The isotopic substitution, performed on the Li and Nb atoms, allows interpretation of the nontrivial mechanism of the phase transition. The ferroelectric phase is more stable than the paraelectric one by 0.32 eV.

First-principles study on the structural, elastic, electronic and optical properties of LiNbO3

The structural, electronic, elastic, mechanical and optical properties of technologically important lithium niobate (LiNbO3) have been investigated by using the first-principle calculations based on density functional theory (DFT) implemented in the CASTEP code. The lattice constants and unit cell volume were calculated from the optimized unit cell, which were in well agreement with the reported theoretical as well as experimental values. Bulk modulus B, Young's modulus Y, shear modulus G, Poisson's ratio σ, elastic anisotropy A and compressibility K were determined based on the computed values of independent elastic constants (C 11, C 12, C 13, C 14, C 33, C 44 and C 66). Electronic band structure and density of states (DOS) demonstrated its semiconducting nature showing a band gap of 3.54 eV. Furthermore, several optical properties, such as absorption coefficient, reflectivity, refractive index, dielectric function, optical conductivity and electron energy loss function have been calculated.

Controllable interlayer space effects of layered potassium triniobate nanoflakes on enhanced pH dependent adsorption-photocatalysis behaviors

Despite the extensive study of two-dimensional layered KNb₃O₈ (KN), there still remains some vital problems need to be clarified for future applications in environmental purification. Here we demonstrated the successful preparation of interlayer-controlled KN nanoflakes using alkaline hydrothermal conditions by adjusting the amount of thiourea in the reaction. This process resulted in KN nanoflakes with a larger specific surface area than previously reported. Moreover, the initial pH of dye solution and discrepant preferential orientation of interlayer peak have been proved to significantly influence the adsorption and photocatalysis performances of KN. In addition, relevant photocatalysis mechanisms have been expounded, by combined the first-principles calculation. The present work could be helpful in revealing the intrinsic adsorption-photocatalysis features of KN and other similar niobates.

Hydrothermal synthesis of ZnO quantum dot/KNb3O8 nanosheet photocatalysts for reducing carbon dioxide to methanol

ZnO quantum dots and KNb₃O₈ nanosheets were synthesized by a two-step hydrothermal method for the photocatalytic reduction of CO₂ to methanol where isopropanol is simultaneously oxidized to acetone . The as-prepared photocatalysts were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and UV-vis absorption spectroscopy (UV-vis). The photocatalytic activity of the materials was evaluated by formation rate of methanol under UV light irradiation at ambient temperature and pressure. The methanol formation rate of pure KNb₃O₈ nanosheets was found to be 1257.21 μmol/g/h, and after deposition of 2 wt % ZnO quantum dots on the surface of KNb₃O₈ nanosheets, the methanol production rate was found to increase to 1539.77 μmol/g/h. Thus, the ZnO quantum dots obviously prompted separation of charge carriers, which was explained by a proposed mechanism for this photocatalytic reaction.

Hierarchical yolk–shell layered potassium niobate for tuned pH-dependent photocatalytic H2 evolution

Tuned pH-dependent H₂ evolutions are achieved by constructing hierarchical KNb₃O₈, which is promising for photocatalysis in mild conditions.

A pseudo-tetragonal tungsten bronze superstructure: a combined solution of the crystal structure of K6.4(Nb,Ta)36.3O94 with advanced transmission electron microscopy and neutron diffraction

K_6.4Nb_28.2Ta_8.1O₉₄ has the same framework as literature's K₂Nb₈O₂₁ but a different distribution of cations over different channels.