Probing the Thermochromic Phase Transition in CuMoO₄ by EXAFS Spectroscopy

Abstract

Extended X‐ray absorption fine structure (EXAFS) spectroscopy at the Mo K‐edge is used to follow the thermochromic γ‐to‐α phase transition in copper molybdate (CuMoO4). The temperature dependence (10–300 K) of the radial distribution function (RDF) for the Mo–O atom pairs in the first coordination shell of molybdenum atoms is reconstructed by the regularization‐like method from the experimental EXAFS spectra. The analysis of the RDFs suggests that the transition occurs gradually within the two‐phase coexistence range of 225–275 K. The local environment of molybdenum atoms transforms upon the γ‐to‐α phase transition from strongly distorted octahedral to less distorted tetrahedral coordination.

Low temperature X-ray absorption spectroscopy study of CuMoO4 and CuMo0.90W0.10O4 using reverse Monte-Carlo method

“…This conclusion agrees with the LCA results suggesting the presence of the 60% and 40% of γ and α phases, respectively (Jonane et al (2018b)).…”

“…The group of four nearest oxygen atoms is responsible for a sharp peak in the RDFs at ∼1.8 Å. These results are in agreement with those obtained by the regularization-like method (Jonane et al (2018b)).…”

“…In such case, the conventional EXAFS analysis is less effective because of a large number of fitting parameters required. Previously, we have employed a regularization-like method to reconstruct the radial distribution functions (RDFs) within the first coordination shell of Mo atoms in CuMoO 4 (Jonane et al (2018b)). Here we extend our analysis beyond the first shell using advanced reverse Monte-Carlo (RMC) calculations based on evolutionary algorithm (Timoshenko et al (2014c)) at several absorption edges simultaneously.…”

Treatment of disorder effects in X-ray absorption spectra beyond the conventional approach

“…( 6), the regularization technique (Babanov et al (1981); Ershov et al (1981); Kuzmin and Purans (2000)) can be used to solve this integral equation as an ill-posed problem without any preliminary assumption on the shape of the RDF. This approach was recently used to reconstruct the local structure in several tungstates MWO 4 (M=Ni, Cu, Zn and Sn) (Kalinko and Kuzmin (2011); Anspoks et al (2014); Kuzmin et al (2015)) and in molybdate CuMoO 4 (Jonane et al (2018b)), where the Jahn-Teller effect is responsible for a strong distortion of structural units. It was demonstrated recently that the RDF G(R) of atoms can be reliably extracted up to distant coordination shells using neural network approach (Timoshenko et al (2018)).…”

The influence of Zn$^{2+}$ ions on the local structure and thermochromic properties of Cu$_{1-x}$Zn$_x$MoO$_4$ solid solutions

“…Indeed, the RMC/EA method has been used by us in the past to demonstrate the sensitivity of XAS to the local structure variations in CuMo 1−x W x O 4 upon the thermochromic phase transition [27]. Moreover, the hysteretic behaviour of the transition has been evidenced by the analysis of the Mo Kedge X-ray absorption near-edge structure (XANES) and EXAFS [17,28,27] and the W L 3 -edge high-energy resolution fluorescence detected XANES (HERFD-XANES) [29].…”