X-ray absorption near edge spectroscopy of thermochromic phase transition in CuMoO4

Abstract

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.

Probing the Thermochromic Phase Transition in CuMoO4 by EXAFS Spectroscopy

“…Note that the EXAFS spectrum at 250 K can be well described by the weighted sum of the two EXAFS spectra corresponding to the γ ‐phase at 225 K and the α ‐phase at 275 K with weights of 60 and 40%, respectively (Figure ). This result agrees well with the linear combination analysis of the Mo K‐edge XANES spectra (see the inset in Figure ) in our previous study …”

“…Temperature dependence of the mean‐square relative displacement (MSRD) σ 2 for the four shortest Mo–O interatomic distances in CuMoO 4 . Inset: the phase transition hysteresis obtained from the Mo K‐edge XANES of CuMoO 4 upon heating and cooling …”

“…Recently, we successfully used a linear combination method to describe the variation of the Mo K‐edge XANES in CuMoO 4 over a wide range of temperatures from 10 to 300 K . We found that the XANES at each temperature can be described by the weighted sum of the two XANES spectra corresponding to pure γ ‐CuMoO 4 and α ‐CuMoO 4 phases measured at 10 and 300 K, respectively.…”

“…Recently, we used X‐ray absorption near edge structure (XANES) spectroscopy to follow the α ‐to‐ γ and γ ‐to‐ α structural phase transitions in CuMoO 4 upon cooling and heating, respectively . While only small variations in XANES were detected at the Cu K‐edge, significant changes in the intensity of the pre‐edge shoulder at the Mo K‐edge were observed.…”

High-temperature X-ray absorption spectroscopy study of thermochromic copper molybdate

“…The samples for the XAS experiments were prepared by mixing CuMoO 4 powder, synthesized using solid-state reaction method as described in [28], with boron nitride powder and pressing into pellets. The thickness of the samples for each absorption edge was optimized to get the value of the absorption edge jump ∆µ x ≈ 1.…”