Disentangling the intricate atomic short-range order and electronic properties in amorphous transition metal oxides

Abstract

Solid state materials with crystalline order have been well-known and characterized for almost a century while the description of disordered materials still bears significant challenges. Among these are the atomic short-range order and electronic properties of amorphous transition metal oxides [aTMOs], that have emerged as novel multifunctional materials due to their optical switching properties and high-capacity to intercalate alkali metal ions at low voltages. For decades, research on aTMOs has dealt with technological optimization. However, it remains challenging to unveil their intricate atomic short-range order. Currently, no systematic and broadly applicable methods exist to assess atomic-size structure, and since electronic localization is structure-dependent, still there are not well-established optical and electronic mechanisms for modelling the properties of aTMOs. We present state-of-the-art systematic procedures involving theory and experiment in a self-consistent computational framework to unveil the atomic short-range order and its role for the electronic properties. The scheme is applied to amorphous tungsten trioxide aWO3, which is the most studied electrochromic aTMO in spite of its unidentified atomic-size structure. Our approach provides a one-to-one matching of experimental data and corresponding model structure from which electronic properties can be directly calculated in agreement with the electronic transitions observed in the XANES spectra.

Comparative study of the around-Fermi electronic structure of 5d metals and metal-oxides by means of high-resolution X-ray emission and absorption spectroscopies

“…From the relative energy separation of the W t 2g and e g states, the crystal field splitting is found to be Á oct ' 3.7 eV, which is in good agreement with the previously reported values for WO 3 (Triana et al, 2017;Yamazoe et al, 2008). However, we would like to stress that the RXES measurements allow for direct crystal field splitting characterization unlike conventional XAS methods (Triana et al, 2017;Yamazoe et al, 2008), which use second-derivative procedures on the X-ray absorption curves. In this way, the RXES methodology and the resulting high-energy resolution XAS functions will allow for determination of much smaller splitting energies.…”

Electrochromic materials and devices for energy efficiency and human comfort in buildings: A critical review

“…These results are in agreement with the fact that trimeric W 3 O 9 molecules tend to form during evaporation [89] and also with computed lowest-energy structures of (WO 3 ) q clusters [90]. Sputtered films appear to be even more disordered and detailed structural models have been obtained from reverse Monte-Carlo modelling of extended X-ray absorption fine structure data [88]; these films can be described as a mixture of corner-sharing and a small amount of edge-sharing polyhedra, with five-fold and a small number of four-fold coordinated W atoms present in addition to the six-fold ones.…”

“…Empirical information on nanostructures in W oxide thin films have been reported many times in the scientific literature, and particularly clear information has been obtained for evaporated and sputter deposited W oxide films investigated by X-ray spectroscopy [87,88].…”

Advanced approach to the local structure reconstruction and theory validation on the example of the W L3-edge extended x-ray absorption fine structure of tungsten

“…A complementary atomistic simulation approach to EXAFS spectrum analysis is based on reverse Monte Carlo (RMC) method [37,38,39,40,41,42,43,44,45,46,47]. It was realised in a number of computer codes as RMCprofile [48], SpecSwap-RMC [49], RMC++ [50] and EvAX [51].…”