Phosphorus Chalcogenide Glasses

Glass formation and local structure in the related system P-Se-Al has also been studied by P and Al NMR which indicates that the local environments of both the P and Al are dominated by the selenium (Hudalla et al. 1998). Although there is evidence of interaction between the Al and P (the formation of four-coordinated P is facilitated by the presence of Al), a more quantitative assessment by Alp P) spin echo double resonance indicates that direct Al-Se-P links occur with less than statistical probability. These results suggest a glass structure which is partially segregated into phosphorus selenide and aluminium selenide-rich regions (Hudalla et al. 1998). 

Aluminophosphates (AIPO4S) are a class of materials which, like the aluminosilicate zeolites, assume open framework structures containing channels of molecular dimensions with molecular sieve properties. Since the AIPO4 structures contain equal numbers of AIO4 and PO4 units there is no necessity for charge-balancing extraframework cations and consequently no sites to provide acid catalytic properties. 

Two-dimensional correlation experiments have also been used to provide structural information about the compounds AIPO4-5 (Fyfe et al. 1996) and AIPO4-I4 (Fyfe et al. 1997). The P MAS NMR spectrum of AIPO4-5 shows a single broad asymmetric 

From Fyfe et al. (1992) by permission of Elsevier Science. B. Two-dimensional A1-- P CP heteronuclear correlation spectrum of AIPO4-8 showing the connectivities between all three of the resolved P sites with both the octahedral and tetrahedral Al jjeaks. Asterisks denote spinning side bands. From Fyfe et al. (1993) by permission of the American Chemical Society. 

Silicon can also be incorporated into AIPO4 frameworks, altering the charge balance and introducing acid sites with their associated catalytic properties. An example of 

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Phosphorus Chalcogenide Glasses P NMR of AIPO4 Molecular Sieves P NMR of Biomaterials... 

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