The effects of chromium oxide on the structure and properties of iron borophosphate glasses

• The solubility limit of Cr2O3 in the iron borophosphate glass is 1 wt.%.
• β-CrPO4 and Fe2(HPO3)3 form when doped Cr2O3 content is more than 1.0 wt.%.
• The addition of Cr2O3 leads to the conversion of Q0 units to Q1 units.
• Tg is improved by Cr2O3 in the glass forming range.

The structure and properties of the iron borophosphate glass containing different amount of Cr2O3 have been investigated by differential thermal analysis (DTA), X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. It is found that the iron borophosphate glass containing less than 1 wt.% Cr2O3 is fully amorphous. Partial crystallization occurs when the content of Cr2O3 is more than 1.0 wt.%, and the main crystalline phases are β-CrPO4 and Fe2(HPO3)3. FTIR spectra and Raman spectra show that the structure of the studied Cr2O3-doped iron borophosphate glasses predominantly consists of orthophosphate (Q0) units and pyrophosphate (Q1) units along with [BO4] units. With the increase of Cr2O3, Q0 units gradually transform to Q1 units, and the addition of Cr2O3 leads to the formation of Cr–O–P bonds in the structural networks of the studied glass. The densities and glass transition temperature increase with the increment of Cr2O3 content up to 1.5 wt.%, suggesting that the glass networks are strengthened by Cr2O3 doping. The conclusions provide an improved understanding of the role of Cr2O3 in the structure of iron borophosphate glasses.