Ca L2,3 edge XANES and Sr K edge EXAFS study of hydroxyapatite and fossil bone apatite

Upon burial, the organic and inorganic components of hard tissues such as bone, teeth, and tusks are subjected to various alterations as a result of interactions with the chemical milieu of soil, groundwater, and presence of microorganisms. In this study, simulation of the Ca L$_{2,3}$-edge X-ray absorption near edge structure (XANES) spectrum of hydroxyapatite, using the CTM4XAS code, reveals that the different symmetry of the two nonequivalent Ca$_{(1)}$ and Ca${(2)}$ sites in the unit cell gives rise to specific spectral features. Moreover, Ca L$_{2,3}$-edge XANES spectroscopy is applied in order to assess variations in fossil bone apatite crystallinity due to heavy bacterial alteration and catastrophic mineral dissolution, compared to well-preserved fossil apatite, fresh bone, and geologic apatite reference samples. Fossilization-induced chemical alterations are investigated by means of Ca L$_{2,3}$-edge XANES and scanning electron microscopy (SEM) and are related to histological evaluation using optical microscopy images. Finally, the variations in the bonding environment of Sr and its preference for substitution in the Ca$_{(1)}$ or Ca$_{(2)}$ sites upon increasing the Sr/Ca ratio is assessed by Sr K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy

Characterization of fossil remains using XRF, XPS and XAFS spectroscopies

Synchrotron radiation micro-X-Ray Fluorescence (m-XRF), X-ray photoelectron (XPS) and X-ray Absorption Fine Structure (XAFS) spectroscopies are applied for the study of paleontological findings. More specifically the costal plate of a gigantic terrestrial turtle Titanochelon bacharidisi and a fossilized coprolite of the cave spotted hyena Crocuta crocuta spelaea are studied. Ca L2,3-edge NEXAFS and Ca 2p XPS are applied for the identification and quantification of apatite and Ca containing minerals. XRF mapping and XAFS are employed for the study of the spatial distribution and speciation of the minerals related to the deposition environment.Fil: Zougrou, I.M.. Aristotle University of Thessalonik; GreciaFil: Katsikini, M.. Aristotle University of Thessalonik; GreciaFil: Pinakidou, F.. Aristotle University of Thessalonik; GreciaFil: Brzhezinskaya, M.. No especifíca;Fil: Papadopoulou, L.. Aristotle University of Thessalonik; GreciaFil: Vlachos, Evangelos. Aristotle University of Thessalonik; Grecia. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Tsoukala, E.. Aristotle University of Thessalonik; GreciaFil: Paloura, E.C.. Aristotle University of Thessalonik; Greci

Probing the Structural Order of Half-Heusler Phases in Sb-Doped (Ti,Zr,Hf)NiSn Thermoelectrics

The nanostructural features of a mechanically alloyed Sb-doped (Ti0.4Zr0.6)0.7Hf0.3NiSn thermoelectric (TE) Half-Heusler (HH) compound were addressed using Transmission Electron Microscopy (TEM) coupled with Energy Dispersive Spectroscopy measurements and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. The EXAFS measurements at the Ni-K, Sn-K, Zr-K, and Hf-L3-edge were implemented in an effort to reveal the influence of Hf and Zr incorporation into the crystal with respect to their previously measured TE properties. The substitution of Ti by Hf and Zr is expected to yield local lattice distortions due to the different atomic sizes of the dopants or/and electronic charge redistribution amongst the cations. However, the material is characterised by a high degree of crystallinity in both the short and long-range order, on average, and the nominal stoichiometry is identified as (Zr0.42Hf0.30Ti0.28)NiSn0.98Sb0.02. The synergistic effect of minimization of extended structural defects or lattice distortions and considerable alloying-induced point defect population contributes to the improved TE properties and leads to the previously reported enhancement of the figure of merit of the mixed HHs