Doris Möncke, Dr. rer. nat. habil., FSGT

Doris Möncke has been working as a glass scientist since she obtained her doctoral dissertation on irradiation induced defects in glasses 2001 at the Otto Schott Institute of Glass Chemistry in Jena. Trained as a chemist, she studied polyvalent ions and structure property correlations in glasses and glass ceramics. Applications of her research include optical, bio- or high strength mechanical glasses, but extend also to modifications of glasses under external forces (mechanical impact, irradiation, or temperature, doping). Doris has first-hand experience in the structural studies of glasses by IR and Raman spectroscopy, having worked five years at the National Hellenic Research Foundation (NHRF) in Athens, Greece, where her interest in archaeometry and ancient glass technology was kindled. In 2017, Doris obtained her habilitation from Jena University, focusing on the role of cations in glasses (from dopants to network former). Doris has worked since as docent and researcher at Alfred University (NY, US) the Universidade Federal de São Carlos (Brazil), and is currently guest professor at Linnæus University (Sweden).

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IR and Raman study of oxy-nitride glasses

Doris Möncke,*1,2 Sharafat Ali,1 Natalia A. Wójcik,1,3 Dimitris Palles2,
Efstratios I. Kamitsos2, Bo Jonson1
1 Linnæus University, Department of Built Environment and Energy Technology, Växjö, Sweden
2 National Hellenic Research Foundation, Theoretical and Physical Chemistry Institute,
Athens, Greece
3 Gdańsk University of Technology, Department of Solid State Physics, Gdańsk, Poland

Various silicate and phosphate glasses with and without nitride addition were structurally characterized by IR and Raman spectroscopy. The studied glass systems include Na-Ca-P-O-N (1), AE-Si-O-N (with AE=Mg, Ca, Sr, Ba)(2), La-Si-O-N (3) as well as the Na-(Li)-Be-O-(N) (4,5) system. The samples were prepared by different techniques such as remelting of pre-prepared glass samples of the oxide systems with Mg and/or Si3N4 powders at 1000–1500 °C under an air or under nitrogen atmosphere or by using metal hydride as a source of modifier cations.

It was observed, that the choice of crucible material (e.g. Pt, porcelain or niobium) was not critical for most silicate glass systems, but that crucible dissolution was a crucial factor for phosphate glasses. The uptake of crucible material by the glass melt was evident by Raman spectroscopy and quantitative analysis, and consequently was also reflected in changes of the glass properties. Figure 1 shows Raman spectra from the Na-Ca-P-O-N system, where the high polarizability of niobium ions leads to the emergence of a niobate related Raman band, evident by the prominent features at 885 to 895 cm-1, which are absent in the base glass melted in platinum crucibles.

Figure 1: Raman spectra for partially crystallized glasses from the Na-Ca-P-O-N series (5: Na18.9Ca4.5P14.6Si0.5Mg0.3Nb0.7O58.7N1.7; 6: Na22.7Ca5.4P18.2Si1.8Mg0.4Nb1.4O44.7N5.3; 7: Na18.2Ca4.6P15.4Si2Mg0.4Nb0.5O56.7N2.1). Spectra have been offset for better comparison. (1)

The glass forming ranges and basic properties have previously been determined for several oxy-nitride systems (1-4) using XRD and microscopy while the chemical composition of all prepared glasses was determined by SEM-EDS. All oxy-nitride glasses were homogenous, but often not transparent. Properties such as transition temperature Tg, refractive index, density, molar volume, mechanical properties, and for some glasses also ion conduction(5), have been obtained and found to correlate directly with the nitrogen content of the materials.

Now, we want to follow up with detailed structural studies, mostly using infrared and Raman spectroscopy. XRD together with µ-Raman and IR microscopic measurements helped in the identification and separation of the vitreous and crystalline phases in the samples, which formed glass ceramics rather than homogenous glasses. Selected properties (Tg and hardness) for the four glasseseries of the AE-Si-O-N system with AE=Mg, Ca, Sr, Ba, are shown in Figure 2.

Figure 2: Transition temperature Tg (left) and hardness (right), increase with incresaing nitrogen content for all glasses of the AE-Si-O-N system (with AE=Mg, Ca, Sr, Ba) (2)

IR reflectance microscopy was also employed for small samples, which did not allow polishing to the flat large surfaces needed for reflectance IR spectroscopy, which on the other hand allows to measure for good quality samples the full range from 30 to 7000 cm-1 and gives the absorption coefficient spectra after Kramer-Kronig-transformation.

For the AE-Si-O-N (AE=Mg, Ca, Sr, Ba) (2) and La-Si-O-N (3) system, thin oxy-nitride films on various substrates, including float glass, Si or Al2O3 had been prepared and were also analysed by transmission IR spectroscopy. These films (see also Figure 3), are homogenous and transparent, showing excellent mechanical strength, even surpassing the bulk material. Their high quality also allowed full optical characterization of the films.

Figure 3: Photographs of thin oxy-nitride films on Si-waver, float glass or saphire as substrate, and on the right, the cross section of a roughly 500 nm thick film, as seen by SEM.(6)

For several glass systems, where refractive index data was available, we determined the anion polarizabilities and applied for the first time the concept of optical basicity to oxy-nitride glasses.

(1)  N. A. Wójcik, B. Jonson, D. Möncke, D. Palles, E. I. Kamitsos, E. Ghassemali, S. Seifeddine, M. Eriksson and S. Ali: Influence of synthesis conditions on glass formation, structure and thermal properties in the system Na2O-CaO-P2O5 doped with Si3N4 and Mg,
submitted to J. Non-Crystalline Solids, February 2018

(2)  S., Ali. and B. Jonson: Compositional effects on the properties of high nitrogen content alkaline-earth silicon oxynitride glasses, AE = Mg, Ca, Sr, Ba.
J. Eur. Ceram. Soc. (2011) 31: 611-618.

(3)  A.S. Hakeem, J. Grins and S. Esmaeilzadeh:
La–Si–O–N glasses – Part I. Extension of the glass forming region, J. Eur. Ceram. Soc. (2007) 27 (16) 4773-4781.

(4)  N. A. Wójcik, B. Jonson, D. Möncke, J. Karczewski, N. Tayara, E. I. Kamitsos and S. Ali:
The influence of BeO addition on the structure and thermal properties of silicate glasses containing alkali ions,
to be submitted to J. Non-Crystalline Solids, April 2018

(5)  N. A. Wójcik, B. Jonson, D. Möncke, R.J. Barczyński, P. Kupracz and S. Ali:
Electrical and mechanical properties of Na2O-CaO-P2O5 glasses doped with SiO2 and Si3N4,
to be submitted to Solid State Ionics April 2018

(6)  S. Ali, B. Paul, R. Magnusson, E. Broitman, B. Jonson, P. Eklund and J. Birch:
Synthesis and characterization of the mechanical and optical properties of Ca-Si-O-N thin films deposited by RF magnetron sputtering,
Surf. Coat. Technol. (2017) 315: 88-94.