Study of vapors sensing materials employing rapid acquisition of total scattering experiments analyzed by the atomic pair distribution function method at Jatobá beamline

Full text: Atomic pair distribution function (PDF) is an attractive technique to analyze X-ray total scattering data. PDF is a powerful characterization tool in material science, and it is an alternative /or complement to conventional X-ray diffraction (XRD) and X-ray absorption spectroscopy. Contrary to XRD that only reflects information about the average structure, PDF analysis allows the detection of small local distortions, bringing information of the local and medium-range order. This method has also been used to study amorphous phases of materials, i.e., those presenting XRD patterns containing broad and low-intensity Bragg peaks. Additionally, it has been useful in structural studies of nanomaterials in which their characteristic sizes limit the proper study by conventional XRD. PDF helps to answer a series of questions regarding local structure, nano-phase detection and quantification, and elucidate anion redox or sensing reactions. The first PDF experiment performed at LNLS was measured at the XDS beamline studying ferroelectric materials with perovskite structure. The following characteristics are mandatory to perform total scattering experiments to be interpreted by PDF: (i) reach high momentum transfer (Q), preferably higher than 20 Å-1; (ii) obtain high resolution in Q and good statistics (high signal-to-noise ratio) for high Q-values; and finally, (iii) use instruments with low background noise, since the data need to have a better signal-to-noise ratio than for Rietveld refinement. The projected beamline, Jatobá, will satisfy all these characteristics. It would reach energy values up to 71 keV, that it is reflected in a Qmax of 37 Å-1 at the 2D detector. We propose to analyze by PDF nanostructures of (Cr,Ti)₂O₃ as a function of temperature and at different atmospheres. With this experiment we expect to elucidate if the surface if affected with the external parameters (temperature and atmosphere) producing nanocluster with distorted structure. (author)