The effect of Fe2O3 substitution for Al2O3 on the phase composition and structure of sodium–aluminum–iron phosphate glasses

• The glasses actually contain Fe(II) and must be related to the system Na2O–Al2O3–FeO–Fe2O3–P2O5.
• The glasses are the most resistant to devitrification at a molar ratio of Al2O3:Fe2O3 ≈ 1.
• Iron in the glasses is present as major Fe(III) and minor Fe(II) both octahedrally coordinated.
• The glass network is composed of ortho- and pyrophosphate units linked by AlO4 and FeO6 units.

The phase composition and structure of sodium–aluminum (iron) phosphate glasses and glass crystalline materials at Fe2O3 substitution for Al2O3 in the glasses of the series (mol%) 40 Na2O, (20 − x) Al2O3, x Fe2O3, 40 P2O5 (I) and 35 Na2O, (20 − x) Al2O3, x Fe2O3, 45 P2O5 (II) were studied by Fourier Transform Infrared (FTIR), Raman, and Mössbauer spectroscopy techniques. The products in series I poured onto a metal plate were found to be amorphous (glasses) while the annealed samples were partly devitrified except for the sample at x = 10 which remained amorphous. The quenched samples of series II contained AlPO4 at high Al2O3 content (x = 0 and x = 5) and were amorphous at high iron content while the annealed samples were mostly devitrified with segregation of ortho- and pyrophosphate phases. The anionic motif of the glasses in both series is mainly composed of ortho- (Q0) and pyrophosphate (Q1) structural units. In the structure of the glasses in series I the Q0 to Q1 ratio remains the same at Al2O3 substitution for Fe2O3 within the whole x range whereas in the structure of the glasses in series II the Q0 to Q1 ratio changes in favor of the Q1 units. Annealing of the quenched samples resulted in splitting of the bands in FTIR due to de-degeneration at formation of crystalline phases. Iron in the glasses is present as major Fe(III) and minor Fe(II) both in primarily octahedral oxygen environment.