materials research J. Synchrotron Rad. (2005). 12, 129–134 doi:10.1107/S0909049504026172 129 Journal of Synchrotron Radiation ISSN 0909-0495 Received 7 June 2004 Accepted 14 October 2004 # 2005 International Union of Crystallography Printed in Great Britain – all rights reserved Synchrotron and simulations techniques applied to problems in materials science: catalysts and Azul Maya pigments Russell R. Chianelli, a * Myriam Perez De la Rosa, a George Meitzner, a Mohammed Siadati, a Gilles Berhault, b Apurva Mehta, c John Pople, c Sergio Fuentes, d Gabriel Alonzo-Nun ˜ez e and Lori A. Polette a a MRTI, University of Texas at El Paso, El Paso, Texas, USA, b LACCO-CNRS, Poitiers, France, c SSRL, Stanford, California, USA, d Centro de Ciencias de la Materia Condensada, UNAM, Ensenada, BC, Mexico, and e Centro de Investigacion en Materiales Avanzados, Chihuahua, Chih, Mexico. E-mail: chianell@utep.edu Development of synchrotron techniques for the determination of the structure of disordered, amorphous and surface materials has exploded over the past 20 years owing to the increasing availability of high-flux synchrotron radiation and the continuing development of increasingly powerful synchrotron techniques. These techniques are available to materials scientists who are not necessarily synchrotron scientists through interaction with effective user communities that exist at synchrotrons such as the Stanford Synchrotron Radiation Laboratory. In this article the application of multiple synchrotron characterization techniques to two classes of materials defined as ‘surface compounds’ is reviewed. One class of surface compounds are materials like MoS 2–x C x that are widely used petroleum catalysts, used to improve the environmental properties of transportation fuels. These compounds may be viewed as ‘sulfide-supported carbides’ in their catalytically active states. The second class of ‘surface compounds’ are the ‘Maya blue’ pigments that are based on technology created by the ancient Maya. These compounds are organic/inorganic ‘surface complexes’ consisting of the dye indigo and palygorskite, common clay. The identification of both surface compounds relies on the application of synchrotron techniques as described here. Keywords: XAFS; WAXS; SAXS; XANES; catalysts; Maya blue. 1. Introduction The availability of high-quality synchrotron radiation and the ability to apply synchrotron techniques routinely to problems in materials science has greatly enhanced our ability to solve materials problems that involve highly disordered, amorphous or surface states. The application of synchrotron techniques to materials problems has been reviewed recently (Gerson et al., 1999; Yoshiki, 2002; Montano & Hiroyuki, 1999). Techniques such as WAXS (wide-angle X-ray scattering), XAFS (X-ray absorption fine structure) and XANES (X-ray absorption near-edge structure) have become routine techniques for the materials scientist, improving our ability to understand diffi- cult issues related to the structure and function of modern poorly crystalline materials. In situ techniques and surface techniques including surface scattering are developing rapidly and will become routine in the near future to help us further understand complex materials. It is the high intensity and stability of synchrotron radiation sources, along with the possibility to select the wavelength of the beam, that make synchrotron techniques so valuable for the problems described here. An example of how a simple synchrotron technique such as synchrotron XRD (X-ray diffraction) can yield new insight into an old problem can be found in a recent paper about the magnetic structure of Aurivillius ceramics (Fuentes et al. , 2002). Members of this class such as BaBi 4 Ti 4 O 15 are of interest because of the high-temperature ferroelectricity and their potential as magnetoelectric sensors. The crystalline structure of these materials is formed by perovskite octahedra, sandwiched between bismuth oxide layers. For temperatures above the Curie point, T c (873–1073 K), Aurivillius crystals adopt centrosymmetric tetragonal structures, with space group Fmmm. In the ferroelectric temperature domain T < T c , tetragonal symmetry breaks down to orthorhombic or monoclinic, with lattice parameters slightly different from those corresponding to the high-temperature configuration. Determining the crystal symmetry group is difficult, but it is