The contribution of static and thermal disorder is one of the largest challenges for the accurate determination of the atomic structure from the extended X-ray absorption fine structure (EXAFS). Although there are a number of generally accepted approaches to solve this problem, which are widely used in the EXAFS data analysis, they often provide less accurate results when applied to outer coordination shells around the absorbing atom. In this case, the advanced techniques based on the molecular dynamics and reverse Monte Carlo simulations are known to be more appropriate: their strengths and weaknesses are reviewed here.

Thermochromic phase transition was studied in CuMoO4 using the Cu and Mo K-edge X-ray absorption spectroscopy in the temperature range of 10-300 K. The hysteretic behavior has been evidenced from the temperature dependence of the pre-edge shoulder intensity at the Mo K-edge, indicating that the transition from brownish-red γ-CuMoO4 to green α-CuMoO4 occurs in the temperature range of 230-280 K upon heating, whereas the α-to-γ transition occurs between 200 and 120 K upon cooling. Such behavior of the pre-edge shoulder at the Mo K-edge correlates with the change of molybdenum coordination between distorted tetrahedral in α-CuMoO4 and distorted octahedral in γ-CuMoO4. This result has been supported by ab initio full-multiple-scattering X-ray absorption near edge structure (XANES) calculations.

The local structure and lattice dynamics in cubic Y2O3 were studied at the Y K-edge by X-ray absorption spectroscopy in the temperature range from 300 to 1273 K. The temperature dependence of the extended X-ray absorption fine structure was successfully interpreted using classical molecular dynamics and a novel reverse Monte Carlo method, coupled with the evolutionary algorithm. The obtained results allowed the temperature dependence of the yttria atomic structure to be followed up to ∼6 Å and to validate two force-field models.

Transparent n-type niobium-doped titanium dioxide thin films (TiO 2 :1.5 at.%Nb) with pronounced thermoelectric properties were produced from a composite Ti:Nb target by reactive magnetron sputtering. The thin films were comprehensively characterized by X-ray diffraction, X-ray photoelectron spectroscopy, optical spectroscopy, electrical conductivity, and thermoelectric measurement techniques. The local structure of the thin films was investigated in detail by X-ray absorption spectroscopy at the Ti and Nb Kedges. A set of radial distribution functions were extracted from the simultaneous analysis of EXAFS data at two absorption edges using the reverse Monte Carlo method. It was found that Nb dopant atoms modify the local environment of the films, but their average structure remains close to that of the anatase phase. This conclusion is also supported by the ab initio simulations of XANES. A very high absolute Seebeck coefficient (S=155 µV/K) for n-type TiO 2 was achieved with Nb doping, yielding a maximum power factor and thermoelectric figure of merit of 0.5 mW•m -1 •K -2 and 0.18 at a temperature of 300 K, respectively, for a 150 nm thick film. From frequencydomain thermoreflectance experiments, a thermal conductivity value of 1.3 W•m -1 •K -1 was obtained for the optimized TiO 2 :Nb film.

Reversible thermochromic phase transition between αand γ-phases was studied in CuMoO 4 and CuMo 0.90 W 0.10 O 4 using X-ray absorption spectroscopy in the temperature range of 10-300 K. Reverse Monte Carlo modelling with evolutionary algorithm approach at several absorption edges simultaneously was applied to extract structural information encoded in the experimental EXAFS spectra. The obtained results show that an addition of 10 mol% of tungsten to CuMoO 4 induces local distortions in the structure and stabilizes the γ-phase, leading to an increase of the phase transition temperature by ∼50-100 K.