P2O5 crystallizes in at least four forms. The most familiar polymorph (see figure) comprises molecules of P4O10. The other polymorphs are polymeric, but in each case the phosphorus atoms are bound by a tetrahedron of oxygen atoms, one of which forms a terminal P=O bond. The O-form adopts a layered structure consisting of interconnected P6O6 rings, not unlike the structure adopted by certain polysilicates.
The P4O10 cagelike structure which provides the basic building block for phosphate glass formers.
^Bitar M, C Knowles J, Lewis MP, Salih V (December 2005). "Soluble phosphate glass fibres for repair of bone-ligament interface". Journal of Materials Science: Materials in Medicine16 (12): 1131–6. doi:10.1007/s10856-005-4718-3. PMID16362212.