WorldWideScience

Sample records for allotropy

  1. Exploring silicon allotropy and chemistry by high pressure – high temperature conditions

    Science.gov (United States)

    Kurakevych, O. O.; Le Godec, Y.; Strobel, T. A.; Kim, D. Y.; Crichton, W. A.; Guignard, J.

    2017-10-01

    Silicon is the second abundant element, after oxygen, in the earth crust. It is essential for today’s electronics because of its ability to show various electronic behaviors that allow covering the numerous fields of cutting-edge applications. Moreover, silicon is not a pollutant and, therefore, is an ideal candidate to replace the actual materials in photovoltaics, like compounds based on the arsenic and heavy metals. It has not replaced them so far because Si is an indirect gap semiconductor and cannot absorb directly the solar photons without thermal agitations of crystal lattice (phonons). This puts it apart from the next-generation applications (light diode, high-performance transistor). That justifies the attempts to create silicon materials with direct gap that can absorb and emit light. Our recent high-pressure studies of the chemical interaction and phase transformations in the Na-Si system, revealed a number of interesting routes to new and known silicon compounds and allotropes. The pressure-temperature range of their formation is suitable for large-volume synthesis and future industrial scaling. The variety of properties observed (e.g. quasi-direct bandgap of open-framework allotrope Si24) allows us to suggest future industrial applications.

  2. Sull’origine di armeno k‘oweay ‘dado’

    Directory of Open Access Journals (Sweden)

    Andrea Scala

    2016-07-01

    Full Text Available Il lessema armeno k‘oweay ‘dado’, registrato nei lessici per lo più con questa forma, conosce almeno due altri allotropi: k‘owē e k‘oway. Il rapporto tra le forme k‘oweay e k‘owē è chiaro: la flessione dei sostantivi in -eay e di quelli in -ē coincide in tutti i casi indiretti (cfr. a titolo di esempio hreay ‘ebreo’ con origine remota in sir. īhūdāyā e mediazione iranica, gen.-dat. sing. hrēi plur. hrēic‘, strum. sing. hrēiw plur. hrēiwk‘ e hiwłē ‘materia, atomo’ < gr. ὕλη, gen.-dat. sing. hiwłēi plur. hiwłēic‘, strum. sing. hiwłēiw plur. hiwłēiwk‘, mentre è distinta nei casi retti (cfr. nom. hreay plur. hreayk‘, acc. hreay plur. hreays contro nom. hiwłē plur. hiwłēk‘, acc. hiwłē plur. hiwłēs e non sono rari i casi di conguaglio analogico tra i due schemi flessionali, con creazione di allotropi al nominativo e all’accusativo; cfr. anche ašteay/aštē ‘lancia’, bazeay/bazē ‘falcone, sparviero’.

  3. Oana Salişteanu Cristea, Prestito latino - Elemento ereditario nel lessico della lingua italiana - Doppioni e varianti, Istituto di Studi Romanzi, Facoltà di Lettere, Università Carolina Praga; Praga 2000, pp. 199

    Directory of Open Access Journals (Sweden)

    Pavao Tekavčić

    2000-12-01

    Full Text Available La ricchezza del lessico italiano dall'antichità ad oggi e la sua complicata stratificazione sono oggetto dell'interesse dei linguisti da più di un secolo e mezzo; eppure, c'è una serie di problemi non studiati a fondo, tuttora aperti e promettenti. Uno di tali temi è la coesistenza di due (o più riflessi di una sola base latina, cioè gli allotropi e doppioni (franc. doublets. Dai tempi di Ugo Angelo Canello (anni 70 dell'Ottocento questo settore del vocabolario non cessa di preoccupare gli studiosi ed il più recente contributo -- importantissimo, diciamolo subito-- che riassume, discute, sistematizza e in gran parte completa quanto fatto finora, è il recentissimo volume della professoressa Oana Sălişteanu Cristea, docente di linguistica italiana (storia della lingua, filologia e dialettologia all'Università di Bucarest. Questo libro è l'oggetto della presente recensione.

  4. Effect of Metallic Nanoparticle Decoration on Graphene Oxide Conductivity

    Science.gov (United States)

    Guliants, Elena; Fernando, Shiral; Watson, Venroy; Wang, Xifan; Gaugler, Elizabeth; Energy Technology and Materials Division Team

    2014-03-01

    Light and strong single-atom-thick carbon derivatives attract a wealth of attention from the research community due to their potential applications. Development of compatible satellite technologies for all-carbon nanoelectronic circuitry is vital for progress in practical applications. Graphene oxide (GO), the closest graphene relative, with its high surface area, unique atomic-layer properties, chemical inertness, and excellent bio-compatibility, has been tested for the applications in energy storage, flexible electronics, sensing technologies, and photovoltaics. GO conductivity enhancement by nanoparticle decoration can drastically improve the field effect transport of charge carriers in thin film transistors. In this study, GO, synthesized using modified Hummer's method, was functionalized with Ag nanoparticles using a two-step sonochemical procedure. Ag nanoparticles were shown to effectively migrate and redistribute when exposed to other carbon allotropies, such as carbon nanotubes and carbon dots. Studies of the effect of Ag precursor concentration and further nanoparticle migration on the conductivity of Ag/GO composites will be discussed within the context of charge carrier transport mechanisms.

  5. Equilibrium p-T Phase Diagram of Boron: Experimental Study and Thermodynamic Analysis

    Science.gov (United States)

    Solozhenko, Vladimir L.; Kurakevych, Oleksandr O.

    2013-01-01

    Solid-state phase transformations and melting of high-purity crystalline boron have been in situ and ex situ studied at pressures to 20 GPa in the 1500–2500 K temperature range where diffusion processes become fast and lead to formation of thermodynamically stable phases. The equilibrium phase diagram of boron has been constructed based on thermodynamic analysis of experimental and literature data. The high-temperature part of the diagram contains p-T domains of thermodynamic stability of rhombohedral β-B106, orthorhombic γ-B28, pseudo-cubic (tetragonal) t'-B52, and liquid boron (L). The positions of two triple points have been experimentally estimated, i.e. β–t'–L at ~ 8.0 GPa and ~ 2490 K; and β–γ–t' at ~ 9.6 GPa and ~ 2230 K. Finally, the proposed phase diagram explains all thermodynamic aspects of boron allotropy and significantly improves our understanding of the fifth element. PMID:23912523

  6. Some of the properties of plutonium and the aluminium-plutonium alloy

    International Nuclear Information System (INIS)

    Abramson, R.; Boucher, R.; Fabre, R.; Monti, H.

    1959-01-01

    1- Study of the physical properties of plutonium. 1) Study of the allotropy of plutonium. a) Thermal analysis: the apparatus used and the measurement technique are briefly described. The transition point temperatures and the corresponding heats of transformation have been determined. Finally, the results of the particular study of certain transition points are given. b) Dilatometry. The dilatometric analysis of the phase changes of plutonium has been carried out by means of the Chevenard dilatometer with photographic recording. The testing conditions (heating and cooling speeds, isotherm plateaux) have been varied in order to determine accurately the characteristics of each transition, particularly the δ → γ transition on cooling. 2) Micrography of plutonium. For the accurate preparation of metallographic samples the electrolytic polishing must be rapid, which implies a mechanical polishing of excellent quality. Information is given on new attacking reagents which show the structure of the metal very clearly. 2- Study of aluminium-plutonium alloys. Comparative study of Al-Pu and Al-U alloys rich in aluminium. a) Thermal analysis. The liquids and fusion temperatures of the eutectic Al-XAl 4 , have been accurately determined. From the measurement of the heats of fusion the exact composition of the eutectic alloy has been determined. b) Thermal treatments. The eutectic coalescence kinetics have been studied by a micrographic method and by following the evolution of hardness. The results obtained show that the phenomenon is more rapid in Al-Pu alloys than in Al-U alloys. c) Micrographic study of the transition XAl 3 → XAl 4 . The peritectic reaction XAl 3 + liq. → XAl 4 has been suppressed by quenching. The transformation of the XAl 3 phase to the solid phase has been studied as well as the effect of small additions of silicon on the kinetics of this reaction. (author) [fr

  7. Characterization of surface electrochemical reactions used in electrochemical atomic layer epitaxy and digital etching

    Science.gov (United States)

    Sorenson, Thomas Allen

    formed on the surface were analogous to bulk allotropes of each element. Differences in the observed structures for Se and Te can be explained by either the smaller atomic size of Se or different allotropy for each element.