| 1. |
- Dussauze, M., et al.
(författare)
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Lithium Ion Conducting Boron-Oxynitride Amorphous Thin Films: Synthesis and Molecular Structure by Infrared Spectroscopy and Density Functional Theory Modeling
- 2013
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:14, s. 7202-7213
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Tidskriftsartikel (refereegranskat)abstract
- Li ion containing oxynitride amorphous thin films are promising materials for electrochemical applications due to their high ionic conductivity, mechanical stability and chemical durability. Here we report on the preparation of Li boron-oxynitride (LiBON) amorphous thin films by rf sputtering of Li-diborate and Li-pyroborate targets in nitrogen atmosphere. The materials produced were subsequently studied by infrared transmittance spectroscopy assisted by density functional theory calculations using representative Li boron-oxide and boron-oxynitride clusters. The combination of experiments and calculations allows us to propose accurate vibrational assignments and to clarify the complex infrared activity of the LiBON films. Both experimental and calculated spectra show that nitrogen incorporation induces significant structural rearrangements, manifested mainly by a change in boron coordination number from four to three, and by the formation of boron-nitrogen-boron bridges. The nature of boron-nitrogen bonding depends on the composition of the sputtering target, with an exponential relationship adequately describing the dependence of B-N stretching frequency on bond length. Besides bonding to two boron atoms by covalent bonds, the nitrogen atoms interact also with Li ions by participating in their coordination sphere together with oxygen atoms. Likely, boron-nitrogen bonding in LiBON films facilitates Li ion transport due to induced charge delocalization within the boron-nitrogen-boron bridges and reduced electrostatic interaction with the Li ions.
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| 2. |
- Efthimiopoulos, I., et al.
(författare)
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Femtosecond laser-induced transformations in ultra-low expansion glass : Microstructure and local density variations by vibrational spectroscopy
- 2018
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 123:23
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Tidskriftsartikel (refereegranskat)abstract
- We report X-ray diffraction, resonance Raman, and infrared (IR) results on pristine ultra-low expansion (ULE) glass, a binary titanosilicate glass with 5.67 mol. % TiO2. ULE processing by femtosecond (fs) laser radiation leads to nanograting writing and photo-darkening for imaging and data storage. We investigate here the vibrational/structural changes induced by fs laser irradiation of ULE at 515 nm. Optical imaging revealed the formation of micro-cavities, and Raman mapping showed molecular oxygen trapped in such cavities of laser-irradiated ULE glass. While titanium in the pristine glass was found predominantly in tetrahedral Ti4+ sites highly dispersed in the silicate matrix, Raman and IR reflectance spectroscopy on laser-irradiated ULE indicated the formation of Ti3+ sites; Ti3+ octahedral sites are formed in the shells of cavities and aggregate in amorphous Ti2O3-type clusters, while the glass around and below cavities contains Ti3+ tetrahedral sites dispersed in the silicate network. Laser-processed ULE glass was found to also exhibit local restructuring of the silicate matrix. Shifts of the strong IR band at about 1080-1100 cm(-1) were translated into changes of the average Si-O-Si bond angle in the laser-transformed areas and found to reflect local density variations; the average local density increases relative to silica glass up to about 8% in the shells of micro-cavities and decreases by about 0.5% in the surrounding material. Chemical processes were proposed to account for photo-darkening and the local structural transformation effect in the probed areas of the fs laser-processed ULE glasses. Published by AIP Publishing.
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| 3. |
- Wójcik, Natalia A., et al.
(författare)
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Influence of synthesis conditions on glass formation, structure and thermal properties in the Na2O-CaO-P2O5 system doped with Si3N4 and Mg
- 2018
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Ingår i: Journal of Non-Crystalline Solids. - : Elsevier. - 0022-3093 .- 1873-4812. ; 494, s. 66-77
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Tidskriftsartikel (refereegranskat)abstract
- Oxynitride phosphate glasses and glass-ceramics were prepared using new synthesis routes for phosphate glasses. Materials were melted from pre-prepared glass samples in the system Na-Ca-P-0 with addition of Mg and/or Si3N4 powders under different preparation conditions. The melting process was conducted at 1000-1500 degrees C either under air or nitrogen atmosphere to obtain materials with different nitrogen content. Their topography and structure were characterized by Confocal Microscopy, Scanning Electron Microscopy, X-ray powder diffraction and Raman and infrared spectroscopy techniques, while their chemical compositions were examined by Energy Dispersive X-ray spectroscopy (EDS). All materials prepared under nitrogen atmosphere were found to contain a relative low quantity of nitrogen and high amount of Nb leached from the crucible. The reaction with the Nb crucible was not previously observed for silicon-based oxynitride glasses. The synthesized materials form two groups: glasses and glass-ceramics. The first ones, were prepared under air and nitrogen atmospheres at temperatures up to 1400 degrees C, and were found to be amorphous and homogeneous. Raman and infrared spectroscopy measurements confirm the presence of amorphous phosphates in the synthesized materials. The samples of the second group were prepared at temperatures above 1400 degrees C and were found to be translucent and partially crystallized. They contain nanocrystallites of calcium and sodium phosphates including hydroxyapatite (HAp). The thermal properties of samples were studied by Differential Scanning Calorimetry (DSC). The obtained glass transition temperatures range from about 360 degrees C to 640 degrees C and exhibit high values for glass-ceramic materials. Stability is improved in the studied glass-ceramics because of the increased degree of network polymerization of the remaining glassy matrix. The approximate fragility index decreases two times for oxynitride materials compared to the primary glass. The synthesized new materials may be competitive to well-known bioactive phosphate glasses thanks to their improved stability by Mg, Si, N and Nb doping.
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| 4. |
- Wójcik, Natalia A., et al.
(författare)
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The influence of Be addition on the structure and thermal properties of alkali-silicate glasses
- 2019
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Ingår i: Journal of Non-Crystalline Solids. - : Elsevier BV. - 0022-3093 .- 1873-4812. ; 521
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Tidskriftsartikel (refereegranskat)abstract
- Be-Na-(Li)-Si oxide glasses containing up to 15 mol% of BeO were prepared. Their structure was characterized by X-ray powder diffraction and Raman as well as infrared spectroscopic techniques, while their chemical compositions were examined by Inductively Coupled Plasma Optical Emission Spectrometry. All materials were found to be amorphous and contain Al contaminations from minor dissolution of the alumina crucibles. The results of Raman and IR spectroscopies showed that BeO addition to Na-(Li)-Si glass systems resulted in the formation of [BeO4/2](2-) tetrahedra which are inserted into the silicate glass network, demonstrating the intermediate glass-forming role of BeO. In parallel, the effective destruction of Si-O-Si bridges was observed by vibrational spectroscopy. The glass transition temperature was studied by Differential Thermal Analysis and found to range from about 431 degrees C to 551 degrees C. A significant increase in T-g by 70 degrees C was found as SiO2 was substituted by up to 15 mol% BeO.
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