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Nitrogenrich La-Si-Al-O-N oxynitride glass structures probed by solid state NMR
Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
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2008 (English)In: Journal of Non-Crystalline Solids, ISSN 0022-3093, E-ISSN 1873-4812, Vol. 354, no 1, 49-60 p.Article in journal (Refereed) Published
Abstract [en]

We investigate the local structures of oxynitride La–Si–(Al)–O–N glasses by 29Si and 27Al magic-angle spinning (MAS) solid state Nuclear Magnetic Resonance (NMR). The glasses studied span an unprecedented range of compositions, up to >50 at.% lanthanum and nitrogen out of the cations and anions, respectively, and achievable through a recently introduced glass preparation route. Transmission as well as scanning electron microscopy verified homogeneous samples over length-scales down to 20 nm. As the nitrogen content of the glasses increased, 29Si NMR evidenced a progressive formation of Si–N bonds, with SiO2N2 tetrahedra dominating in the nitrogen-rich glass networks. In the oxygen-rich end of the series, aluminum is predominantly present in tetrahedral coordination as AlO4, whereas the glasses with highest nitrogen contents have a major fraction of AlO3N structural units. Trends in isotropic 29Si and 27Al chemical shifts and 27Al quadrupolar couplings are compared with results of La–Si–Al–O glasses and are discussed in relation to the glass compositions and their proposed structures.

Place, publisher, year, edition, pages
Elsevier , 2008. Vol. 354, no 1, 49-60 p.
Keyword [en]
Oxynitride glass, La–Si–Al–O glass, Glass structure, Rare-earth Silicate, 29Si NMR, 27Al NMR, TEM, Cross-polarization, Cation distributions
National Category
Inorganic Chemistry
Research subject
Materials Chemistry
Identifiers
URN: urn:nbn:se:su:diva-24539DOI: 10.1016/j.jnoncrysol.2007.07.027ISI: 000252686600007OAI: oai:DiVA.org:su-24539DiVA: diva2:197761
Note
Part of urn:nbn:se:su:diva-7169Available from: 2007-11-06 Created: 2007-11-06 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Novel Route of Oxynitride Glass Synthesis and Characterisation of Glasses in the Ln-Si-O-N and Ln-Si-Al-O-N Systems
Open this publication in new window or tab >>Novel Route of Oxynitride Glass Synthesis and Characterisation of Glasses in the Ln-Si-O-N and Ln-Si-Al-O-N Systems
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The present work has been primarily focused on the glass forming region in the La-Si-O-N system, and attempts have been made to find glass forming regions by adopting a new synthesis route to produce glasses in oxynitride system. This goal can be attained by adding a network modifier in its metallic form instead of as an oxide. In this kind of synthesis, the metallic modifier reacts with nitrogen, which gives a strongly exothermic reaction at particular temperature. The resulting sudden increase in the temperature of the system enables the mixture to react with other components at an early stage of the synthesis. This also provides a high degree of mixing in the melt, and results in larger glass forming regions than reported until now (Figure A shows La from 30 to 62 e/o and nitrogen from 9 of 68 e/o in the La-Si-O-N system). The better property values (Tg-Tc, hardness and refractive index) were achieved over the whole compositional range in the systems.

Similarly, glasses containing Al were prepared in the Ln-Si-Al-O-N system, where Ln = La, Sm, Gd, Ho, Dy, and in the Ln-Si-O-N system, with Ln = Pr, Sm, Gd, Dy. Both systems were examined to study the properties at various nitrogen contents, which can be as high as 70 e/o. Glasses were prepared from one particular glass composition in the Pr-Si-O-N system by replacing Pr with various other La components, in order to study the effect of lanthanide substitution on the properties.

Figure A. The solid line encloses the glass forming region in the La-Si-O-N system, as determined in the present work. The dotted line represent the glass forming region according to the literature; details are given in figure 11.

A new synthesis route has extended the glass forming region, allowing a detailed study of properties such as hardness, glass transition temperature (Tg), glass crystallization temperature (Tc), density and refractive index. Comprehensive studies of properties may give better understanding of the glass structure. The glass transition temperatures range from 950 to 1100°C, and crystallization temperatures from 1050 to 1250°C; the hardness can be as high as 12 GPa and the refractive index attains the value 2.3 in the La-Si-O-N system. Hardness and refractive index were measured in both glass systems (Ln-Si-O-N and Ln-Si-Al-O-N) when substituting cations, and a detailed study of replacing La with Pr in the La-Si-O-N system yielded substantial effects on the properties of the glasses.

Higher values of hardness were found: ~13 GPa when applying load of one kg, and an increase with decreasing cation radius was noted in both the Ln-Si-O-N and the Ln-Si-Al-O-N system, containing of 63 and 61 e/o nitrogen, respectively. The hardness increases as the lanthanide ionic radius decreases, and becomes as high as 13.5 GPa in the Dy-Si-O-N system, and the refractive index is 2.3 in the La-Si-O-N system. A linear increase in the properties Tg-Tc, hardness and refractive index with increasing Pr content was found in the Pr-(La)-Si-O-N system.

Place, publisher, year, edition, pages
Stockholm: Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi, 2007. 91 p.
National Category
Chemical Sciences
Research subject
Inorganic Chemistry
Identifiers
urn:nbn:se:su:diva-7169 (URN)978-91-7155-523-6 (ISBN)
Public defence
2007-11-09, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 12 A, Stockholm, 10:00
Opponent
Supervisors
Available from: 2007-11-06 Created: 2007-11-06Bibliographically approved
2. Structural Investigations of Complex Glasses by Solid-state NMR
Open this publication in new window or tab >>Structural Investigations of Complex Glasses by Solid-state NMR
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This PhD thesis presents structural investigations of amorphous inorganic materials: oxide and oxynitride glasses and mesoporous bioactive glasses (MBGs), by solid-state Nuclear Magnetic Resonance (NMR).

Lanthanum oxide and oxynitride [La-Si-(Al)-O-(N)] glasses have a large number of potential applications due to their physical properties. In our work we have studied, compared to previous investigations, significantly expanded ranges of glass compositions (for oxynitride glasses, including samples of very high nitrogen content, up to 53 % out of the anions). We have estimated local environments of 29Si and 27Al structural units (their coordination, polymerization degree and number of N incorporated into tetrahedral units) in the materials. We have suggested a random Al/Si distribution along with almost uniform non-bridging oxygen atoms distribution in aluminosilicate glasses.

Silicon nitride was used as precursor in the oxynitride glass synthesis. We studied both α- and β-modifications of silicon nitride, 15N-enriched, as well as fully (29Si, 15N)-enriched samples. We have shown that the linewidths of 15N NMR spectra are dominated by J(29Si-15N) coupling in 29Si315N4 sample.

Mesoporous bioactive glasses in the CaO-SiO2-P2O5 system show superior bioactivity (the ability to form a hydroxycarbonate apatite layer on the glass surface when exposed to body fluids) compared to conventional bioactive glasses due to their large surface area and uniform pore-size distribution. Previous studies suggested a homogeneous cation distribution over the MBG samples on a 10−20 nm length-scale. From our results, on the other hand, we may conclude that Si and P is not intimately mixed. We propose a structural model, in which the pore walls of MBGs are composed of a silica network, and a phosphate phase is present as nanometer-sized clusters that are dispersed on the pore wall.

Place, publisher, year, edition, pages
Stockholm: Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi, 2009. 62 p.
Keyword
glass, glass structure and properties, NMR, magic angle spinning, chemical shift
National Category
Physical Chemistry
Research subject
Physical Chemistry
Identifiers
urn:nbn:se:su:diva-8565 (URN)978-91-7155-816-9 (ISBN)
Public defence
2009-03-19, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 8 C, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2009-02-26 Created: 2009-02-18 Last updated: 2010-01-26Bibliographically approved

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