Infrared and Raman spectra of Ga2O3–P2O5 glasses

The structure of xGa2O3(1−x)P2O5(0.15 ⩽ x ⩽ 0.4) glasses is studied by infrared (IR) and Raman spectroscopy. The results of quantitative electron microprobe analysis reveal that two sets of glasses are formed with compositions corresponding to the gallium meta and pyrophosphates. Crystalline Ga(PO3)3 metaphosphate is also obtained and its IR and Raman spectra recorded in order to examine the spectral differences glass → crystal. The IR spectra of metaphosphate glasses show bands at 1250, 930, 775 and 485 cm−1 which, are assigned to the νasPO2,νasPOP, νsPOP and δPO2 modes of the metaphosphate chain. In the Raman spectra are found patterns due to symmetric modes of PO2 terminal and POP bridging bonds as well as features due to vibrations of GaO4 tetrahedra and Ga–O–P bridges. Comparisons of the spectra of glasses with those of the crystal indicate that the interaction of Ga with the polyphosphate anions is more covalent in the glasses. The bands observed in the spectra of pyrophosphate glasses provide evidence for the involvement of ortho-, pyro- and polyphosphate groupings in the glass structure. The Raman spectra of both sets of glasses display intense low frequency bands, which we assigned to a symmetric bending of Ga–O–P bridging bonds involving four-coordinated gallium atoms. It is concluded that structure of Ga2O3–P2O5 glasses is a highly polymerized network consisting of a variety of phosphate anions cross-linked by GaO4 tetrahedra. This account on glass structure is consistent with the great glass forming ability of the compositions studied.