In this contribution we present a detailed study of the effect of the addition of small to intermediate amounts of P 2 O 5 (up to 7.5 mol %) on the network organization of metaluminous sodium aluminosilicate glasses employing a range of advanced solid state NMR methodologies. The combined results from MAS, MQMAS (multiple quantum MAS), or MAT (magic angle turning) NMR spectroscopy and a variety of dipolar based NMR experiments 27 Al{ 31 P}-, 27 Al{ 29 Si}-, 29 Si{ 31 P}-, and 31 P{ 29 Si}-REDOR (rotational echo double resonance) NMR spectroscopy as well as 31 P{ 27 Al}-and 29 Si{ 27 Al}-REAPDOR (rotational echo adiabatic passage double resonance) NMRallow for a detailed analysis of the network organization adopted by these glasses. Phosphate is found as Q P 2 , Q P 3 , and Q P 4 (with the superscript denoting the number of bridging oxygens), the Q P 4 units can be safely identified with the help of 31 P MAT NMR experiments. Al exclusively adopts a 4-fold coordination. The withdrawal of a fraction of the sodium cations from AlO 4 units that is needed for charge compensation of the Q P 2 units necessitates an alternative charge compensation scheme for these AlO 4 units via formation of Q P 4 units or oxygen triclusters. The dipolar NMR experiments suggest a strong preference of P for Al with an average value of ca. 2.4 P−O−Al connections per phosphate tetrahedron. P is thus mainly integrated into the network via P−O−Al bonding, the formation of Si−O−P bonding plays only a minor role.

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Melt-derived metaluminous (Al/Na = 1) aluminosilicate glasses in the system SiO 2 −Al 2 O 3 −Na 2 O−P 2 O 5 were prepared with P 2 O 5 and SiO 2 contents varying from 0 to 7.5 and 50 to 70 mol %, respectively. The glass structure was investigated by X-ray absorption near edge structure, far-and medium-infrared, and polarized Raman spectroscopic techniques. The results indicate the incorporation of phosphate into the aluminosilicate network not only as partially depolymerized groups but also as fully polymerized groups charge-balanced by aluminate units in Al−O−P bonds. A new analysis method based on polarized Raman spectra in the bending frequency range indicates a preference of phosphate to reorganize the smallest ring structures. Changes in the glass transition temperature with the increase in phosphate content were found to be consistent with the depolymerization of the network structure shown by spectroscopy. By contrast, increasing the silica content by substituting SiO 4 for AlO 4 tetrahedra, while keeping the phosphate content constant, was found to have a negligible effect on network polymerization. Still, the glass transition temperature decreased and correlated with a far-infrared sodium band shift to higher frequency. This was interpreted as local changes in bond strength caused by complex interactions between the different network formers and sodium ions.

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.