“…The latter findings in combination with the results from the glasses melted in alumina crucibles at 900°C indicate an overall increase in L, G, K, and E along with a slight reduction of ν with increasing melting time and temperature and, thus, higher Al 2 O 3 concentration. These trends are in good agreement with previous observations, 51,60 and support the conclusions derived from our thermal ( Figure 1) and structural analyses (Figures 3-5) that the introduction of Al 2 O 3 from alumina crucibles strengthens the glass network through the creation of P-O-Al-O-P cross-links between the phosphate chains, thus enhancing overall network rigidity and connectivity. 61 Moreover, the compositional tendency of ν agrees well with a commonly accepted model according to which glasses with a higher network dimensionality typically exhibit smaller values of ν as compared to glasses with a weakly cross-linked network structure.…”
Section: Resultssupporting
confidence: 93%
“…Table ). Accordingly, a distinct shoulder developed near 1100 cm −1 with increasing melting time in alumina crucibles, which can be attributed to the symmetric P–O stretching mode of Q 1 units . For the longest melting times the distinct ν s (P–O–Si) band (present at 587 cm −1 for the glasses melted in platinum or silica crucibles) disappeared completely, owing to the dominant formation of P–O–Al bonds (Figure B).…”
Section: Resultsmentioning
confidence: 95%
“…Accordingly, a distinct shoulder developed near 1100 cm −1 with increasing melting time in alumina crucibles, which can be attributed to the symmetric P-O stretching mode of Q 1 units. 43,46,51 For the longest melting times the distinct ν s (P-O-Si) band (present at 587 cm −1 for the glasses melted in platinum or silica crucibles) disappeared completely, owing to the dominant formation of P-O-Al bonds ( Figure 3B). Comparing the effect of temperature, we note that the Raman spectrum of glass 900Al12, alumina-melted glass at 900°C for 12 hours, still shows the s PO − 2 band at 1161 cm −1 , which is characteristic for Q 2 in metaphosphate chains, as seen in Figure 3A.…”
Ceramic crucibles are known to corrode in contact with glass melts. Here, we investigate the effect of alumina and fused silica crucibles on the composition, structure, and properties of silicophosphate glasses. Glasses in the system 0.3 Na2O‐0.6 P2O5‐0.1 SiO2 were melted in platinum, alumina, or fused silica crucibles at 900°C or 1200°C for 0.5‐12 hours. Al2O3 and SiO2 were found to leach from the crucibles into the glass melt and alter the glass composition: Al2O3 content increased with melting temperature and time, resulting in up to 10 mol% Al2O3; SiO2 from fused silica crucibles was also introduced into the glass, resulting in a 25% higher SiO2 content compared to the nominal composition. Glass density, transition temperature, thermal expansion, and mechanical properties were strongly affected by these compositional changes. Based on vibrational spectroscopy, this is explained by increasing numbers of P–O–Al or P–O–Si bonds, resulting in a depolymerization of the phosphate network, and ionic cross‐linking by high field strength aluminum or silicon ions. With increasing alumina content, P–O–Si bonds were replaced by P–O–Al bonds. 31P and 27Al MAS NMR spectra revealed that aluminum is present in sixfold coordination exclusively and fully bonded to phosphate species, connecting phosphate groups by P–O–Al–O–P bonds.
“…The latter findings in combination with the results from the glasses melted in alumina crucibles at 900°C indicate an overall increase in L, G, K, and E along with a slight reduction of ν with increasing melting time and temperature and, thus, higher Al 2 O 3 concentration. These trends are in good agreement with previous observations, 51,60 and support the conclusions derived from our thermal ( Figure 1) and structural analyses (Figures 3-5) that the introduction of Al 2 O 3 from alumina crucibles strengthens the glass network through the creation of P-O-Al-O-P cross-links between the phosphate chains, thus enhancing overall network rigidity and connectivity. 61 Moreover, the compositional tendency of ν agrees well with a commonly accepted model according to which glasses with a higher network dimensionality typically exhibit smaller values of ν as compared to glasses with a weakly cross-linked network structure.…”
Section: Resultssupporting
confidence: 93%
“…Table ). Accordingly, a distinct shoulder developed near 1100 cm −1 with increasing melting time in alumina crucibles, which can be attributed to the symmetric P–O stretching mode of Q 1 units . For the longest melting times the distinct ν s (P–O–Si) band (present at 587 cm −1 for the glasses melted in platinum or silica crucibles) disappeared completely, owing to the dominant formation of P–O–Al bonds (Figure B).…”
Section: Resultsmentioning
confidence: 95%
“…Accordingly, a distinct shoulder developed near 1100 cm −1 with increasing melting time in alumina crucibles, which can be attributed to the symmetric P-O stretching mode of Q 1 units. 43,46,51 For the longest melting times the distinct ν s (P-O-Si) band (present at 587 cm −1 for the glasses melted in platinum or silica crucibles) disappeared completely, owing to the dominant formation of P-O-Al bonds ( Figure 3B). Comparing the effect of temperature, we note that the Raman spectrum of glass 900Al12, alumina-melted glass at 900°C for 12 hours, still shows the s PO − 2 band at 1161 cm −1 , which is characteristic for Q 2 in metaphosphate chains, as seen in Figure 3A.…”
Ceramic crucibles are known to corrode in contact with glass melts. Here, we investigate the effect of alumina and fused silica crucibles on the composition, structure, and properties of silicophosphate glasses. Glasses in the system 0.3 Na2O‐0.6 P2O5‐0.1 SiO2 were melted in platinum, alumina, or fused silica crucibles at 900°C or 1200°C for 0.5‐12 hours. Al2O3 and SiO2 were found to leach from the crucibles into the glass melt and alter the glass composition: Al2O3 content increased with melting temperature and time, resulting in up to 10 mol% Al2O3; SiO2 from fused silica crucibles was also introduced into the glass, resulting in a 25% higher SiO2 content compared to the nominal composition. Glass density, transition temperature, thermal expansion, and mechanical properties were strongly affected by these compositional changes. Based on vibrational spectroscopy, this is explained by increasing numbers of P–O–Al or P–O–Si bonds, resulting in a depolymerization of the phosphate network, and ionic cross‐linking by high field strength aluminum or silicon ions. With increasing alumina content, P–O–Si bonds were replaced by P–O–Al bonds. 31P and 27Al MAS NMR spectra revealed that aluminum is present in sixfold coordination exclusively and fully bonded to phosphate species, connecting phosphate groups by P–O–Al–O–P bonds.
“…To obtain quantitatively the Boson peak frequency, it is necessary to use a function which reproduces-well the reduced intensity I red (ω) and takes into account the asymmetric shape of the Boson peak. For this, we used a log-normal function 56 ,Figure 6( a ) Stokes-side of the reduced low-frequency Raman spectra of silica and binary aluminosilicate glasses after subtraction of quasi-elastic scattering (QES) contributions. The solid line represents an exemplary log-normal fit of the experimental data of vitreous silica (type R300) used to estimate the Boson peak frequency.…”
In binary aluminosilicate liquids and glasses, heterogeneity on intermediate length scale is a crucial factor for optical fiber performance, determining the lower limit of optical attenuation and Rayleigh scattering, but also clustering and precipitation of optically active dopants, for example, in the fabrication of high-power laser gain media. Here, we consider the low-frequency vibrational modes of such materials for assessing structural heterogeneity on molecular scale. We determine the vibrational density of states VDoS g(ω) using low-temperature heat capacity data. From correlation with low-frequency Raman spectroscopy, we obtain the Raman coupling coefficient. Both experiments allow for the extraction of the average dynamic correlation length as a function of alumina content. We find that this value decreases from about 3.9 nm to 3.3 nm when mildly increasing the alumina content from zero (vitreous silica) to 7 mol%. At the same time, the average inter-particle distance increases slightly due to the presence of oxygen tricluster species. In accordance with Loewensteinian dynamics, this proves that mild alumina doping increases structural homogeneity on molecular scale.
“…All spectra exhibit the excess in g(ω) as compared to the Debye prediction which is typical for glassy materials (with D (ω) = 3ω 2 /ω 3 ≈ ω 2 , with the Debye frequency ω ). In order to estimate the Boson peak frequency quantitatively the reduced intensity was fitted with a log-normal function [34,56], taking into account the asymmetric shape of the Boson peak. In Fig.…”
Section: Vibrational Density Of States and Boson Peakmentioning
Microscopic deformation processes lie at the origin of defect formation
on glass surfaces, thus determining the material’s resistance to
scratching and mechanical failure. While the macroscopic strength of
most glasses is not directly depending on material composition, local
deformation and flaw initiation are strongly affected by chemistry and
atomic arrangement. Aside empirical insight, however, the structural
origin of the fundamental deformation modes remains largely unknown.
Experimental methods which probe parameters on short or intermediate
length-scale such as atom-atom or super-structural correlations are
typically applied in the absence of alternatives. Drawing on recent
experimental advances, we now probe spatial variations in the
low-frequency vibrational density of states which result from sharp
contact deformation of vitreous silica. From direct observation of
deformation-induced variations on the characteristic length-scale of
molecular heterogeneity, we argue that rigidity fluctuation on the scale
of a few nanometers governs the deformation process of inorganic
glasses.
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