Εξειδίκευση τύπου :	Άρθρο σε επιστημονικό περιοδικό
Τίτλος:	Molecular dynamics investigation of mixed-alkali borate glasses: Short-range order structure and alkali-ion environments
Δημιουργός/Συγγραφέας:	[EL] Βεγίρη, Αλίκη[EN] Vegiri, Aliki [EL] Βαρσάμης, Χρήστος-Πλάτων Ε.[EN] Varsamis, Christos-Platon E. [EL] Καμίτσος, Ευστράτιος Ι.[EN] Kamitsos, Efstratios I.
Εκδότης:	American Physical Society
Τόπος έκδοσης:	COLLEGE PK
Ημερομηνία:	2009-11
Γλώσσα:	Αγγλικά
ISSN:	1098-0121
DOI:	10.1103/PhysRevB.80.184202
Περίληψη:	Structural properties of mixed-alkali borate glasses, 0.3[(1-x)Li(2)O-xCs(2)O]-0.7B(2)O(3) and 0.3[(1-x)Li(2)O-xNa(2)O]-0.7B(2)O(3), have been studied by molecular dynamics simulations at T=300 K and for several values of the alkali mixing parameter, x, to explore structural foundations of the mixed-alkali effect (MAE). The short-range order (SRO) structure was found to consist of borate tetrahedra, B empty set (-)(4), and of neutral, B empty set (3), and charged, B empty set (2)O(-), triangular units [empty set =bridging oxygen atom]. The abundance of B empty set (-)(4) units was found to decrease from Li to Cs and to exhibit negative deviation from linearity in Li-Cs glasses. However, no appreciable change in SRO structure was detected in mixed Li-Na glasses. Even though alkali metal (M) ions occupy in mixed glasses sites, i.e., coordination environments with O atoms, similar to those formed in single alkali borates, mixing was found to affect the M-O bonding properties of dissimilar alkalis in an opposite manner. Thus, for both systems investigated here the Li ion-coordination environment was found to become better defined and the Li-O interactions to strengthen upon alkali mixing, whereas the Cs-O and Na-O interactions become progressively weakened. The origin of these trends was traced to cationic environments formed around nonbridging oxygen (NBO) atoms in glass; it was found that the dominant cation configurations around NBOs consist of dissimilar cations in mixed-alkali glasses. The formation of dissimilar ion pairs affects by polarization effects the bonding and vibrational properties of metal ions in their oxide sites. This was demonstrated for Li-Cs glasses by both experimental and calculated far infrared spectra, where the metal ion-oxide site vibrations are strongly active. It was discussed that the preference of unlike-alkali ion pairing around NBOs and the consequent drastic reduction in the number of NBOs that sense like-cations could provide a structural explanation for the MAE.
Τίτλος πηγής δημοσίευσης:	Physical Review B
Τόμος/Κεφάλαιο:	80
Τεύχος:	18
Σελίδες:	[12]
Θεματική Κατηγορία:	[EL] Φυσική[EN] Physics
Λέξεις-Κλειδιά:	borate glasses boron compounds caesium compounds infrared spectra lithium compounds molecular dynamics method polarisation sodium compounds Physics, Condensed Matter
Αξιολόγηση από ομότιμους (peer reviewed):	Ναι
Όροι και προϋποθέσεις δικαιωμάτων:	This article may be downloaded for personal use only. Any other use requires prior permission of the author and American Physical Society (APS). This article apperas in "Physycal Review B 80, 184202 – Published 2 November 2009" and can be found at the following URL on the APS website: https://journals.aps.org/prb/abstract/10.1103/PhysRevB.80.184202
Ηλεκτρονική διεύθυνση περιοδικού (link) :	http://prb.aps.org/
Εμφανίζεται στις συλλογές:	Ινστιτούτο Θεωρητικής και Φυσικής Χημείας (ΙΘΦΧ) - Επιστημονικό έργο