Royal Swedish Academy of Sciences Physica Scripta Phys. Scr. 89 (2014) 044006 (6pp) doi:10.1088/0031-8949/89/04/044006 Analysis of extended x-ray absorption fine structure data from copper tungstate by the reverse Monte Carlo method Janis Timoshenko 1 , Andris Anspoks 1 , Aleksandr Kalinko 1,2 and Alexei Kuzmin 1 1 Institute of Solid State Physics, University of Latvia, Kengaraga Street 8, LV-1063 Riga, Latvia 2 Synchrotron SOLEIL, l’Orme des Merisiers, Saint-Aubin, BP 48, F-91192 Gif-sur-Yvette, France E-mail: janis.timoshenko@gmail.com Received 6 June 2013, revised 10 October 2013 Accepted for publication 14 October 2013 Published 25 February 2014 Abstract The static disorder and lattice dynamics of crystalline materials can be efficiently studied using reverse Monte Carlo simulations of extended x-ray absorption fine structure spectra (EXAFS). In this work we demonstrate the potentiality of this method on an example of copper tungstate CuWO 4 . The simultaneous analysis of the Cu K and W L 3 edges EXAFS spectra allowed us to follow local structure distortion as a function of temperature. Keywords: copper tungstate, EXAFS, reverse Monte Carlo, wavelet transform (Some figures may appear in colour only in the online journal) 1. Introduction Transition-metal tungstates are technologically important materials with interesting optical, magnetic and ferroelectric properties [1–3], whose optimization and tailoring require a precise knowledge of atomic structure and lattice dynamics. X-ray absorption spectroscopy is a suitable tool to address this problem, because it is able to provide information about the local environment of a particular chemical element [4]. A complex structure and low symmetry of tungstates makes the interpretation of the extended x-ray absorption fine structure (EXAFS) using conventional methods very challenging [5]. Therefore, we have turned to a more advanced approach based on the reverse Monte Carlo (RMC) algorithm. The RMC method is a numerical technique that is able to reconstruct the three-dimensional atomic structure of a material by minimizing the difference between theoretically calculated and experimental structure-related data [6]. Usually it is applied to the investigations of disordered compounds [7, 8]. Recently we have demonstrated that RMC–EXAFS analysis can be successfully used to investigate relatively simple crystalline structures such as germanium and rhenium trioxide [9, 10]. An important element of our RMC implemen- tation, proposed in [9], is the use of wavelet transform (WT) for the comparison of experimental and calculated EXAFS spectra in direct and reciprocal spaces simultaneously [11, 12]. Recently [13] we have applied the RMC method to the analysis of EXAFS data from a significantly more complex system such as cobalt tungstate. In the presented study, we continue the RMC–EXAFS investigation of crystalline tungstates by applying the developed method to copper tungstate (CuWO 4 ), with the aim of reconstructing the local environment around the copper and tungsten atoms. We demonstrate that only simultaneous analysis of the Cu K and W L 3 edges EXAFS spectra provides a reliable structural solution. 2. Experimental details Polycrystalline CuWO 4 powder was synthesized using a co-precipitation technique by a reaction of proper amounts of aqueous solutions of CuSO 4 ·5H 2 O and Na 2 WO 4 ·2H 2 O at 20 ◦ C. The obtained precipitate was washed, dried and finally annealed in air for 8 h at 800 ◦ C. X-ray diffraction and Raman spectroscopy measurements show that the powder sample has single-phase triclinic symmetry [14, 15]. X-ray absorption measurements were performed in transmission mode at the HASYLAB/DESY C(CEMO) 0031-8949/14/044006+06$33.00 1 © 2014 The Royal Swedish Academy of Sciences Printed in the UK