1,721,210 research outputs found
Crystallographic texture analysis: A non-invasive metallographic technique in archaeometry
No full textProfile-fitting of single crystal diffraction data
No full textProfile-fitting methods have received great attention in the area of structure analysis from powder diffraction data. Although the use of profile fitting for the reliable extraction of integrated intensities from single-crystal diffraction data has long been proposed in the literature, a limited number of applications and tests of the method have been performed on single-crystal X-ray or neutron diffraction profiles. The profile-fitting technique is here employed to extract integrated intensities from two troublesome data sets of single-crystal diffraction profiles, one affected by multiple scattering effects (X-ray) and the other showing scan truncation (neutrons). It is shown that die proposed implementation of the profile-fitting procedure has great advantages in producing reliable integrated intensities compared with conventional integration methods. Furthermore, during die data processing, any anomalous diffraction profile is easily detected and proper analysis of instrumental background and scan-truncation effects is performed. The method thus allows effective evaluation of the quality of the treated data set. It is proposed that the profile-fitting technique for the extraction of single-crystal integrated intensities be used routinely when diffraction data of superior quality are needed for crystal structure analysis
Chemical and mineralogical studies on hominid remains from Sangiran, Central Java (Indonesia).
No full textLow temperature SR-XRPD study of akermanite-gehlenite solid solution
No full textLow temperature thermal expansion coefficients of members of the solid solution gehlenite (ge)-åkermanite (åk) were measured by synchrotron radiation X-Ray powder diffraction. The linear thermal expansion coefficient is maximum for a composition with about 50 % content of åk. In åk-rich compositions an incommensurate modulated structure is present. The ge-åk solid solution shows a non-ideal behaviour, with negative excess volume near the ge end-member
Caratterizzazione e tecnologia della produzione ceramica nel territorio alto e medio polesano tra l'età del Bronzo recente e la prima età del Ferro
No full textThermal expansion and phase transitions in akermanite and gehlenite
No full textThermal expansion has been measured by laboratory and synchrotron X-ray powder diffraction for end-member (a) over circle kermanite (ak, Ca2MgSi2O7) and gehlenite (ge, Ca2Al2SiO7) in the range 20-1,500 K. In ak in the range 340-390 K, there is a negative linear thermal expansion in [001] direction. This is related to the phase transition from an incommensurate modulated structure (IC) to a normal one (N). The volumetric mean thermal expansion coefficients for ak and ge, obtained with a linear fit of the experimental data in the temperature range 298-1,400 K, are respectively 32.1x10(-6) and 28.3x10(-6) K-1. The variation of the c/a ratio with temperature, due to different thermal expansion along the crystallographic axes, can be related to the different behaviour of the tetrahedral layers in the N and IC phases. Analysis of the variation of the superstructure peaks intensity across the phase transition confirms the tricritical behaviour of the IC/N transition in ak
The crystal chemistry of julgoldite-Fe3+ from Bombay, India, studied using synchrotron X-ray powder diffraction and 57Fe Moessbauer spectrocopy
No full textThe crystal structure of julgoldite-Fe3+ from Bombay, India, was investigated by 57Fe Mössbauer spectroscopy and synchrotron X-ray powder diffraction. Only ferric iron was detected in the Mössbauer measurements and it occurs at two different octahedral sites in the atomic ratio 20:80. Based on Rietveld refinements, the Fe3+ cations are located at the X- and Y-octahedral sites with atomic percentages of about 25% and 75%, respectively. The resulting chemical formula of the Bombay julgoldite sample is crystal-chemical considerations. Such analysis cannot give quantitative results for the valence state of mixed-valence cations in pumpellyite-type minerals and their intracrystalline partitioning behavior. Assignments of the Mössbauer absorption doublets and an analysis of Fe-intracrystalline partitioning behavior are discussed with reference to previous works on different pumpellyite-type minerals
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