Abstract
Determination of the atomic-scale structures of certain fine-grained minerals using single-crystal X-ray diffraction (XRD) has been challenging because they commonly occur as submicron and nanocrystals in the geological environment. Synchrotron powder diffraction and scattering techniques are useful complementary methods for studying this type of minerals. In this review, we discussed three example studies investigated by combined methods of synchrotron radiation XRD and pair distribution function (PDF) techniques: (1) low-temperature cristobalite; (2) kaolinite; and (3) vernadite. Powder XRD is useful to determine the average structure including unit-cell parameters, fractional atomic coordinates, occupancies and isotropic atomic displacement parameters. X-ray/Neutron PDF methods are sensitive to study the local structure with anisotropic atomic displacement parameters (ADP). The results and case studies suggest that the crystal structure and high-quality ADP values can be obtained using the combined methods. The method can be useful to characterize crystals and minerals that are not suitable for single-crystal XRD.
Highlights
The determination of high-quality crystal structure is becoming increasingly critical to advanced science and technology [1,2,3,4]
Rietveld refinement from synchrotron X-ray diffraction (XRD) data provide the high quality of average structure of the tetragonal cristobalite in space group P41 21 2 symmetry with unit cell parameters, atomic coordinates, and bond distances/angles, which is compared with previous tetragonal cristobalite from
We investigated the natural vernadite from ferromanganese crust using combined synchrotron radiation XRD, pair distribution function (PDF), and high-resolution transmission electron microscopy (TEM)
Summary
The determination of high-quality crystal structure is becoming increasingly critical to advanced science and technology [1,2,3,4]. For example, some metastable low-temperature phases and clay minerals that have been challenged to prepare as single crystals for single-crystal X-ray diffraction analysis [7] Another example is the case of nanominerals and nanocrystals that is not available for the single-crystal method [8]. Synchrotron radiation sources combined with advanced algorithms have led to high-resolution powder diffraction data allowing detailed characterization of minerals and materials including nano- and micro-structural characteristics with grain size, shapes, and preferred orientation [20,21,22,23,24]. PDF technique from total scattering data has been of much interest in studying the local structure of amorphous and crystalline phases [4,25,26]. The powder XRD method is useful to determine the average structure including isotropic atomic displacement parameters (Uiso ) [33], by contrast, the PDF method appears to be sensitive to the local structure and anisotropic displacement parameters (ADPs) [7,34,35]
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