First‐principles study of structural, electronic, elastic, and optical properties of cubic KNbO₃ and KTaO₃ crystals

Abstract

Cubic KNbO3 and KTaO3 crystals are studied using the first‐principles VASP code. By employing local density approximation (LDA), GGA‐PBE, and HSE06, the lattice parameters are optimized and compared with available experimental data, and the best agreement is achieved with HSE06. Electronic structures such as density of states, band structures, and charge‐density distribution are discussed in detail for both crystals. The single‐crystal elastic constants, polycrystalline elastic modulus, compressibility, Poisson's ratio, and anisotropy factors are obtained from the Voigt–Reuss–Hill approximation. The elastic anisotropy is modeled and visualized in the light of the elastic properties of both systems. The bandgaps of the two crystals are calculated with LDA, PBE, HSE06, and GW approximations (GW0), and the results of HSE06 and GW0 agree well with experimental data. Then the more reliable optical properties of KNbO3 and KTaO3 are acquired based on the bandgaps with HSE06, in which the previous scissors operator correction is avoided. Both crystals are brittle, and KTaO3 exhibits higher hardness and stiffness than KNbO3. Some novel results, such as Debye temperatures, sound velocities, and the extreme values of Young's modulus are obtained.

Structural, electronic, optical and photocatalytic properties of KTaO3 with NiO cocatalyst modification

“…In this respect, first-principles density functional theory (DFT) calculations can be useful, which have been extensively applied in studying structural, electronic and optical properties of bulk, surfaces and interfacial structures of KTaO 3 . 41–47 Theoretical results have provided reasonable explanations and reliable predictions on experiments. In this work, we have constructed a NiO/KTaO 3 slab model and performed DFT computations to study the structural details and stability of the interfacial structure, to investigate the electronic and optical properties, to explore the carrier migration at interface, and to reveal the mechanism of the enhancement of photocatalytic activity by loading NiO cocatalyst on KTaO 3 surface.…”

“…Further investigations on each component suggest that the VBM and CBM of KTaO 3 slab in the interface are mostly comprised of O 2p states and Ta 5d states, respectively, which are similar with those in bulk. 41 As to NiO side in the interface, the VBM is primarily characterized by the mixture of Ni 3d and O 2p states, while the CBM dominantly comes from Ni 3d states.…”

“…Before building NiO/KTaO 3 interfacial structure, fully optimizations are carried out for bulk phases. According to previous investigations, 41,69 the cubic phase of KTaO 3 with a space group of Pm 3m is adopted in the present work. The crystal structures of bulk NiO and KTaO 3 are shown in Fig.…”

Influence of LiTaO3(0001) and KTaO3(001) Perovskites Structures on the Molecular Adsorption of Styrene and Styrene oxide: A Theoretical Insight by Periodic DFT Calculations

“…As can be seen, the K atom is at the origin, Ta is in the center and the three oxygen atoms are in the center of three different faces. [53] Hexagonal and tetragonal LiTaO 3 structures, respectively, are shown in Figure 3b and 3c. It should be noted that in several studies it has been reported that LiTaO 3 belongs to the R3c crystallographic group of hexagonal classification, [54] even when there are reports of tetragonal structure [55] (see LiTaO 3 bulk structure of Supplementary Material).…”

Investigation of anisotropic mechanical properties of textured KSr2Nb5O15 ceramics via ab‐initio calculation and nanoindentation

“…Firstly, simulations are performed on a perfect (i.e., defect-free) crystal structure, but (in reality) defects occur in KSN ceramics. 24,25 Secondly, actual KSN ceramics are polycrystalline materials and grain boundaries have an influence on the experimental results (see Figure 8). The effect of the boundaries is neglected in the simulations.…”