Dora Ilieva

Infrared and Raman spectra of Ga2O3–P2O5 glasses

Abstract The structure of x Ga 2 O 3 (1−x) P 2 O 5 (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(PO 3 ) 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 ν as PO 2 , ν as POP, ν s POP and δPO 2 modes of the metaphosphate chain. In the Raman spectra are found patterns due to symmetric modes of PO 2 terminal and POP bridging bonds as well as features due to vibrations of GaO 4 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 Ga 2 O 3 –P 2 O 5 glasses is a highly polymerized network consisting of a variety of phosphate anions cross-linked by GaO 4 tetrahedra. This account on glass structure is consistent with the great glass forming ability of the compositions studied.

FT–IR and Raman spectra of Gd phosphate crystals and glasses

Abstract IR and Raman spectra of x Gd 2 O 3 (1− x )P 2 O 5 glasses ( x =0.22–0.31) are reported with emphasis on glassy Gd(PO 3 ) 3 and the crystalline forms emerging upon its devitrification. Increasing the concentration of Gd 2 O 3 from 0.22 to 0.26 mole fractions leads to an abrupt lowering of the highest observed P–O stretching frequency of 25 cm −1 . The spectral shift is related to changes in both the coordination of the lanthanide ion and the increase in metal to phosphorus ratio. The comparison of vibrational spectra of vitreous gadolinium metaphosphate ( x =0.25) with those of its crystalline analogs reveals a decrease in POP and PO 2 bond angles in glass. The changes observed are consistent with an elongation of P–O − terminal and P–O–P bridging bonds in the PO 4 tetrahedra. The redistribution of band frequencies is explained with the more covalent interaction of Gd 3+ with polyphosphate anions in glasses. The spectra of (Gd 2 O 3 ) 0.27 (P 2 O 5 ) 0.73 and (Gd 2 O 3 ) 0.31 (P 2 O 5 ) 0.69 glasses contain the characteristic bands of the metaphosphate structure along with features due to vibrations of PO 3 end groups. Their presence is interpreted in terms of the progressive fragmentation of the polyphosphate chains at these glass compositions.