Local Structure of Cobalt Tungstate Revealed by EXAFS Spectroscopy and Reverse Monte Carlo/Evolutionary Algorithm Simulations

EXAFS spectroscopy is an element-specific method that can provide perhaps the most extensive information on the local atomic structure and lattice dynamics for a broad class of materials. Conventional methods of EXAFS data treatment are often limited to the nearest coordination shells of the absorbing atom due to the difficulties in accurate accounting for the large number of correlated structural parameters that have to be included in the analysis. In this study we overcome this problem by applying novel simulation-based method: reverse Monte Carlo simulations, coupled with the evolutionary algorithm and with a powerful signal processing technique-wavelet transform. This complex approach was applied to the analysis of the W L₃-edge and Co K-edge EXAFS spectra of crystalline CoWO₄, which exists in antiferromagnetic state below 55 K. Temperature dependence of the local environment up to 4.3 Å around both metal ions was reconstructed in the range from 10 K to 300 K, and the rigidity of the tungstate structure due to zigzag chains of WO₆ and CoO₆ octahedra was analyzed.