Dielectric Properties of Reduced Heterogeneous Silica-Titania Glasses

We have studied the frequency and temperature dependences of the dielectric properties of a heterogeneous silica-titania (SiO2-TiO2) glass by ac impedance spectroscopy measurements in the temperature range 25-700 degrees C and the frequency range 40-10(7) Hz. The heterogeneous glass was prepared by the controlled heat treatment of a homogenous SiO2-TiO2 glass, containing similar to 7.5 wt% TiO2, in a reducing atmosphere to create a microstructure consisting of many discrete particles of the rutile/anatase TiO2 phase dispersed in a homogeneous SiO2-rich glassy matrix. Unlike the homogeneous SiO2-TiO2 glass, which exhibited only one electrical/dielectric dispersion, presumably due to ion hopping, the heterogeneous glass material exhibited two distinct electrical responses in the impedance formalism. We attributed these contributions to the two-phase microstructure and explained the dielectric behavior in terms of the Maxwell-Wagner relaxation arising at the interfaces between the TiO2 crystals and the SiO2-rich matrix phase.