Effects of doping CeO2/TiO2 on structure and properties of silicate glass

In order to elucidate the effects of doping CeO2/TiO2 on the structure and physical properties of silicate glass, glasses with composition 72SiO(2)-3Al(2)O(3)-10Na(2)O-10K(2)O-5CaO doped with varied ratios of CeO2/TiO2 were synthesized by melt-quenching method and were characterized by X-ray diffraction, infrared and Raman spectrometry, UV-Visible spectrophotometry and micro-indentations. X-ray diffraction conforms the amorphous state of doped glasses. The spectroscopic analysis reveals that doping CeO2 alone results in depolymerization of glass network and narrowed distribution of Q(n) (Si-O tetrahedral with n bridging oxygen atoms), while doping TiO2 singly or combined with CeO2 favors the enhanced polymerization of network and regains a broader Q(n) distribution relative to doping CeO2 alone. It is proposed that doped cerium and titanium in glass exists in multivalent state and the former in presence of trivalent state preferentially acts as modifier inducing network depolymerization, whilst the latter in form of tetrahedral tends to interconnect network units as intermediate. Doped cerium in trivalent state contributes mainly to the red-shift of absorption edge while titanium suppresses such change of absorption band. Either adding cerium alone or co-doping with titanium will result in decreased optical band gap due to the structural modifications. The relatively loosened structure due to depolymerization induced by cerium is responsible for the decline in hardness and E-modulus but rising in fracture toughness, whereas network compactness by virtue of interconnectivity of titanium and structural densification may account for the increase of hardness and E-modulus at the cost of slight loss of fracture toughness. For silicate glasses co-doped cerium and titanium, the mechanical properties should be the synergy of the two opposite mechanism. (C) 2014 Elsevier B. V. All rights reserved.