Peter P. Bihuniak

Structures, spectra and related properties of group IVB-doped vitreous silica☆

Abstract Vibrational spectra and related physical properties were analyzed for titanium-, zirconium- and hafnium-containing vitreous silicas on the basis of glass structure. Linear functional relationhips were found between both partial molar volume and refractivity, and the dopant concentration throughout the dopant range examined. Analysis of the data suggested four-fold coordination with oxygen atoms by titanium atoms with greater coordination by zirconium and hafnium atoms. Raman and difference infrared spectra for these glasses showed an intensity decrease of the v3 (F2) band at 1068 cm−1 accompanied by the emergence of a band at circa 950cm−1 whose exact wavenumber was defined by the dopant species ( gv Hf > gv Zr > gv Ti ) and, in the case of TiO2- containing glasses, a band at 1110 cm−1. The intensities of these bands were proportional to the dopant concentration. Empirical spectral analysis suggested that upon TiO2 addition Ti-atoms bonded to a single oxygen atom of a SiO4-unit, while upon zirconia and hafnia addition each metal atom bonded to two oxygen atoms of a SiO4-unit. These structural models were consistent with ion coordination predictions based upon the physical property measurements.

Ionic conductivity in doped fused silica

DC ionic conductivity was measured over 300–800 C in specimens of type-I fused silica doped with various levels of Al2O3/M2O ratio (M = alkali) using blocking and non-blocking electrodes. Although the values of the conductivity depended upon the measurement technique, all the data showed an Arrhenius behavior with the values of activation energies ranging from 35 kcal/mole to 20 kcal/mole for various alkali ions below 500 °C. A slight decrease in activation energy was seen in most of the samples at temperatures greater than 500 °C. When the resistivity at a particular temperature was plotted as a function of Al2O3/M2O ratio, a broad minimum in resistivity was seen between the ratios of 4–12. These results are discussed in terms of the AlO4− and nonbridging oxygen sites in the fused silica structure.