Changes in the Electrical Conductivity and Catalytic Property of Vanadium Iron Borophosphate Glasses with Crystallization

Glasses were prepared in the V 2 O 5 −P 2 O 5 −B 2 O 3 system containing Fe 2 O 3 and were crystallized to examine the changes in the structure, as well as the catalytic and the electrical properties. The glasses were annealed in a graphite mold at a temperature above the glass transition temperature for 1 h and were heat-treated at the crystallization temperature for 1 h, 6 h and 12 h, respectively. Fourier-transform infrared spectroscopy (FTIR) was employed to analyze the structural changes of the V−O bonds after crystallization while the X-ray photoelectron spectroscopy (XPS) analysis indicated a decrease in V 5+ and an increase in V 4+ amounts. The X-ray diffraction (XRD) analysis indicated that a new crystalline phase of non-stoichiometric Fe 0.12 V 2 O 5 was formed after 1 h of heat treatment. Structural changes induced by the crystallization were analyzed by determining the molecular volume from the sample density. The conductivity and the catalytic property were examined based on the migration of V and Fe ions exhibiting different valence states with crystallization. Both the conductivity and the catalytic property improved after the samples had been crystallized at the crystallization peak temperature ( T p ). Furthermore, as compared to the sample heat treated for 1 h, the conductance and catalytic properties were improved for samples crystallized at T p for 6 h and 12 h.