The effect of PO2,5 and AlO1,5 additions on structural changes and crystallization behavior of SiO2-TiO2 sol-gel derived glasses and thin films

Abstract

SiO2-TiO2-PO2,5 (STP) and SiO2-TiO2-AlO1,5 (STA) glasses were prepared by sol-gel processing. Their infrared absorption spectra (IR), differential thermal analysis curves (DTA) and X-ray diffraction patterns (XRD) have been recorded. In the SiO2-TiO2 system, the chemical homogeneity of the sol-gel glass could be evaluated by the relative concentration of Si-O-Ti heterocondensation comparing to Si-O-Si homocondensation. For the STA system, a gradual decrease of the Si-O-Ti/Si-O-Si band ratio (based on IR spectra) with the addition of Al2O3 is observed, with the simultaneous formation of Si-O-Al and Ti-O-Al bounds, i.e Al3+ ions are dissolved in the SiO2-TiO2 glass matrix and do not promote glass-in-glass phase-separation in the composition range of 0–15 mol% AlO1.5. In the STP system, on the other hand, P=O bond IR stretch in the ternary glasses indicates that P=O free PO2O2/2− tetrahedra are formed, rather than the double bonded POO3/2 tetrahedra that usually occur in binary SiO2-P2O5 glasses. It can be concluded that SiO2-TiO2-P2O5 glass separates into a SiO2-rich phase and a TiO2(P2O5)-rich phase. During heat-treatment in STA system only anatase precipitates, even at T ~ 1,000 °C, while in for STP, anatase (TiO2) or (TiO)2P2O7 (TOP) crystals precipitate at ~600 °C, depending on the P2O5 concentration. The major crystal phase, cristobalite, precipitated at ~1,000 °C and at ~1,200 °C, the P-containing phase melts.