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Transition from a phosphate to niobate network structure in vitreous Nb2O5–NaPO3.

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Titel: Transition from a phosphate to niobate network structure in vitreous Nb2O5–NaPO3.
Autoren: Salmon, Philip S., Girón Lange, Esther, Zeidler, Anita, Bradtmüller, Henrik, Ensuncho, Laureano, Cuello, Gabriel J., Eckert, Hellmut
Quelle: Journal of Chemical Physics; 10/14/2025, Vol. 163 Issue 14, p1-17, 17p
Schlagwörter: PHOSPHATES, NIOBATES, CHEMICAL speciation, NUCLEAR magnetic resonance spectroscopy, SELF-consistent field theory
Abstract: The structure of (Nb2O5)x(NaPO3)1−x glasses was re-visited by combining neutron and high energy x-ray diffraction with Raman scattering over a wide composition range. The results were interpreted by reference to the phosphorus atom speciation found from a novel analysis of 31P magic angle spinning nuclear magnetic resonance spectra [Ensuncho et al., J. Am. Chem. Soc. 147, 31147 (2025)]. The results indicate a distorted octahedral coordination environment for the Nb atoms across the composition range. The measured x-dependence of (i) the mean numbers of non-bridging oxygen (NBO) atoms and P–O–P and P–O–Nb connections per phosphate group, and (ii) the fraction of oxygen atoms in Nb–O–Nb connections, are described by a self-consistent analytical model in which there is a preferential formation of heteronuclear P–O–Nb bonds within a network structure formed by 4- and 6-coordinated P and Nb atoms, respectively, such that P–O–P connections are absent when the niobia content exceeds x ∼ 0.22. At smaller x, the non-bridging oxygen atoms are distributed among the P- and Nb-centered polyhedral units. The model provides a connectivity density that accounts for the rapid increase in the glass transition temperature with increasing Nb2O5 content and shows that the enhancement to the non-linear optical properties for x > 0.2 is related to a more rapid increase with x in the fraction of oxygen atoms involved in polarizable Nb–O–Nb connections. The methodology also suggests that the dissolution rate measured for the (Nb2O5)x(Na2O)0.4(P2O5)0.6−x glass series is dependent on the proportion of P–O–P linkages. [ABSTRACT FROM AUTHOR]
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Abstract:The structure of (Nb<subscript>2</subscript>O<subscript>5</subscript>)<subscript>x</subscript>(NaPO<subscript>3</subscript>)<subscript>1−x</subscript> glasses was re-visited by combining neutron and high energy x-ray diffraction with Raman scattering over a wide composition range. The results were interpreted by reference to the phosphorus atom speciation found from a novel analysis of <sup>31</sup>P magic angle spinning nuclear magnetic resonance spectra [Ensuncho et al., J. Am. Chem. Soc. 147, 31147 (2025)]. The results indicate a distorted octahedral coordination environment for the Nb atoms across the composition range. The measured x-dependence of (i) the mean numbers of non-bridging oxygen (NBO) atoms and P–O–P and P–O–Nb connections per phosphate group, and (ii) the fraction of oxygen atoms in Nb–O–Nb connections, are described by a self-consistent analytical model in which there is a preferential formation of heteronuclear P–O–Nb bonds within a network structure formed by 4- and 6-coordinated P and Nb atoms, respectively, such that P–O–P connections are absent when the niobia content exceeds x ∼ 0.22. At smaller x, the non-bridging oxygen atoms are distributed among the P- and Nb-centered polyhedral units. The model provides a connectivity density that accounts for the rapid increase in the glass transition temperature with increasing Nb<subscript>2</subscript>O<subscript>5</subscript> content and shows that the enhancement to the non-linear optical properties for x > 0.2 is related to a more rapid increase with x in the fraction of oxygen atoms involved in polarizable Nb–O–Nb connections. The methodology also suggests that the dissolution rate measured for the (Nb<subscript>2</subscript>O<subscript>5</subscript>)<subscript>x</subscript>(Na<subscript>2</subscript>O)<subscript>0.4</subscript>(P<subscript>2</subscript>O<subscript>5</subscript>)<subscript>0.6−x</subscript> glass series is dependent on the proportion of P–O–P linkages. [ABSTRACT FROM AUTHOR]
ISSN:00219606
DOI:10.1063/5.0290349