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Tonietto Serena Nestola Fabrizio Redhammer Gunther J. Silvestri Alberta Molin Gianmario Bruno Marco 《Applied Physics A: Materials Science & Processing》2011,103(1):207-212
The mineral inclusions of two orange glass tesserae from paleo-Christian mosaics were investigated in order to derive the
melting temperature reached during their production (sourced from Padua and Vicenza, Veneto region, Italy). In particular,
clinopyroxene crystals were studied by single-crystal X-ray diffraction and electron microprobe WDS analysis. The crystals
show C2/c symmetry, typical of disordered Ca/Na and Mg/Al distributions indicating high-temperature of formation (>700°C). The cation
site populations were obtained by combining results from the two experimental techniques enabled us to derive the following
stoichiometric formula:
lM2[Ca0.819Na0.172Mn0.006K0.003]M1[Mg0.765Fe3+0.210 Cu0.015Ti0.006Zn0.006]T[Si1.933Al0.037Sn0.024]O6\begin{array}{l}{}^{M2}[\mathrm{Ca}_{0.819}\mathrm{Na}_{0.172}\mathrm{Mn}_{0.006}\mathrm{K}_{0.003}]{}^{M1}[\mathrm{Mg}_{0.765}\mathrm{Fe}^{3+}_{0.210}\\[3pt]\quad{}\mathrm{Cu}_{0.015}\mathrm{Ti}_{0.006}\mathrm{Zn}_{0.006}]{}^{T}[\mathrm{Si}_{1.933}\mathrm{Al}_{0.037}\mathrm{Sn}_{0.024}]\mathrm{O}_{6}\end{array} 相似文献
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G. Artioli I. Angelini F. Nestola 《Applied Physics A: Materials Science & Processing》2013,110(2):371-377
A scarab found in grave 25 of the Monte Prama necropolis, near Cabras, Oristano, Sardinia, is of special importance for the archaeological interpretation and dating of this important archaeological site. The object has been misinterpreted in the past as composed by bone: recent archaeometric analyses showed that it is a glazed steatite of Egyptian origin and that the altered surface contains interesting phases crystallized during the high-temperature interaction of the Mg-rich talc core with the alkali-rich glass used for glazing. A novel single crystal X-ray diffraction analysis of one of the phases indicates that it is a new compound having the milarite-osumilite structure type, with a peculiar composition close to (Na1.52K0.12□0.36)(Mg3)(Mg1.72Cu0.16Fe0.12)(Si11.4Al0.6)O30, not reported for naturally occurring minerals. The structural and crystal chemical features of the compound, together with the known high-temperature stability of the series, allow a complete interpretation of the glazing process and conditions, based on direct application of the glaze on the steatite core with subsequent treatment at temperatures above 1000 °C. 相似文献
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Marco De La Pierre Marco Bruno Chiara Manfredotti Fabrizio Nestola Mauro Prencipe Claudio Manfredotti 《Molecular physics》2014,112(7):1030-1039
We present an accurate ab initio study of the structure and surface energy of the low-index (100), (111) and (110) diamond faces, by using the hybrid Hartree–Fock/density functional B3LYP Hamiltonian and a localised all-electron Gaussian-type basis set. A two-dimensional periodic slab model has been adopted, for which convergence on both structural and energetic parameters has been thoroughly investigated. For all the three surfaces, possible relaxations and reconstructions have been considered; a detailed geometrical characterisation is provided for the most stable structure of each orientation. Surface energy is discussed for all the investigated faces. 相似文献
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First‐principle modelling of forsterite surface properties: Accuracy of methods and basis sets
![]() Raffaella Demichelis Marco Bruno Francesco R. Massaro Mauro Prencipe Marco De La Pierre Fabrizio Nestola 《Journal of computational chemistry》2015,36(19):1439-1445
The seven main crystal surfaces of forsterite (Mg2SiO4) were modeled using various Gaussian‐type basis sets, and several formulations for the exchange‐correlation functional within the density functional theory (DFT). The recently developed pob‐TZVP basis set provides the best results for all properties that are strongly dependent on the accuracy of the wavefunction. Convergence on the structure and on the basis set superposition error‐corrected surface energy can be reached also with poorer basis sets. The effect of adopting different DFT functionals was assessed. All functionals give the same stability order for the various surfaces. Surfaces do not exhibit any major structural differences when optimized with different functionals, except for higher energy orientations where major rearrangements occur around the Mg sites at the surface or subsurface. When dispersions are not accounted for, all functionals provide similar surface energies. The inclusion of empirical dispersions raises the energy of all surfaces by a nearly systematic value proportional to the scaling factor s of the dispersion formulation. An estimation for the surface energy is provided through adopting C6 coefficients that are more suitable than the standard ones to describe O? O interactions in minerals. A 2 × 2 supercell of the most stable surface (010) was optimized. No surface reconstruction was observed. The resulting structure and surface energy show no difference with respect to those obtained when using the primitive cell. This result validates the (010) surface model here adopted, that will serve as a reference for future studies on adsorption and reactivity of water and carbon dioxide at this interface. © 2015 Wiley Periodicals, Inc. 相似文献
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