Mechanistic insights on the electronic properties and electronic/atomic structure aspects in orthorhombic SrVO₃ thin films: XANES–EXAFS study

Abstract

Correlations among the B-O6 octahedra distortions, existing polymorphous phases, band structures and electronic conductivities of ABO perovskites are matters for debate and require a deep understanding of their local atomic/electronic structures and diverse assets. In this study, to illustrate the distortion in V-O6 octahedra and its implication on the band structure and electronic properties, spectroscopic investigations on the RF-sputtering grown insulating SrVO thin films were employed using X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). V K-edge and V L-edge XANES, along with atomic multiplet calculations, have confirmed the 4+ oxidation state of V ions in the pristine and annealed SrVO thin films. Lower t/e peak intensity ratio and smaller energy separation between t and e peaks in the O K-edge XANES spectra, compared to the VO reference sample, have confirmed a larger V-O6 distortion in the orthorhombic SrVO thin films. Moreover, from the EXAFS data analysis, the local orthorhombic structure has been identified in the pristine and annealed SrVO thin films, compelling significant distortion in the V-O6 octahedra. Dimerization in the vanadium chains and V-V twisting, caused by V-O6 octahedra distortion, manifests a miscellaneous ligand field interaction between O 2p and V 3d orbitals and facilitates (i) a larger separation between the bonding and antibonding d orbitals and (ii) an upward shift of the π* band in the band structure, leading to larger band gaps in the insulating SrVO thin films. Our spectroscopy results may open up new avenues for the mechanism of insulating/conducting character in other complicated perovskite materials using XANES-EXAFS.

Electronic structure and luminescence assets in white-light emitting Ca2V2O7, Sr2V2O7 and Ba2V2O7 pyro-vanadates: X-ray absorption spectroscopy investigations

“…36,37 The FE-SEM images ruled out the formation of fascinating morphologies (i.e., nano-rod, nano-wire or other structures) and, therefore, the observed luminescence properties are expected to be related only to the electronic/atomic structure properties but not due to the diverse surface/ interface related phenomena in nanostructures. 16 In the present study, the existence of V ions in Ba 2 V 2 O 7 sample is responsible for such spectral features. We have not seen any ambiguous spectral feature of secondary phases and, thus, the XANES spectra at Ca L-edge, Sr K-edge and Ba L-edge can convince the 2+ valence state of alkali earth elements and strengthened our XRD results of single phase nature of the samples.…”

“…Although, it is a dipole-forbidden transition but originates because of the combination of strong 3d-4p mixing and overlap of the metal 3d orbitals with the surrounding O 2p orbitals. 16,38,39 Above the edge-energy, a strong peak is present in every spectrum which originates due to the dipole-allowed 1s-4p transitions followed by the other higher energy features from the transitions to higher np states and other multiple scattering contributions or, simply, the EXAFS signals. 16,38,39 It is noticeable from the Fig.…”

“…A marginal distortion in the metal-oxygen polyhedra can affect the hybridization between the O 2p and metal d orbitals, which indeed regulate the band structure near the Fermi level and, consequently, the electronic/optical properties of the compounds. 16,17 Optical properties and illumination performance of the compounds are categorically determined by the electronic structure around the stimulated ions and energy transfer processes among them. [18][19][20][21][22] In case of vanadium-based optical materials, the (VO 4 ) 3À groups obey broad and strong chargetransfer (CT) absorption bands near the UV region and, thus, produce broad-emission spectra related to the electronic/ atomic structure of the compound where the V ions are coordinated by the four O ligands.…”

Investigation on cation distribution and luminescence in spinel phase γ-Ga3−δO4 : Sm nanostructures using X-ray absorption spectroscopy

“…In this regard, X-ray absorption spectroscopy (XAS), with its two branches of X-ray absorption near edge structure (XANES) and extended X-ray absorption ne structure (EXAFS), becomes the important elemental characterization technique and has been known to be highly sensitive to the local electronic/atomic structure properties and effectively overcomes the issue of sensitivity to the structure and electronic structure characterization of small sized, poorly crystalline or embedded nanostructures. [26][27][28] In the last few years, probing the local symmetry of the diluted doped elements, 29,30 quantication of the valence state changes of host metal ions upon foreign element doping, [31][32][33] changes in the orbital occupancy, 34,35 and variation in the crystal eld effects 36,37 have been studied for various compounds using the XANES. On the other side, EXAFS, due to the sensitivity to the local atomic structure, has become a powerful probing tool for determining the variation in the coordination number and bond lengths of the constituent elements of the probed material.…”

“…On the other side, EXAFS, due to the sensitivity to the local atomic structure, has become a powerful probing tool for determining the variation in the coordination number and bond lengths of the constituent elements of the probed material. [32][33][34][35][36][37][38][39][40] Besides providing detailed experimental and simulated results on the Ga 2 O 3 polymorphous compounds, the XANES-EXAFS analysis presented in this article addresses various aspects. Firstly, O K-edge XANES spectra were examined to specically look into the diversity in the oxygen environment of g-Ga 3Àd O 4 and b polymorphous phases and to assimilate the effect of Sm insertion on the metal 4s/4p and O 2p orbital hybridization.…”