Preparation and Structure of Thallium and Silver Germanate Glasses

Abstract

Binary thallium and silver germanate glasses containing up to 36 mole % Tl₂O or 25 mole % Ag₂O were prepared by carefully heating mixtures of GeO₂ and TlNO₃ or Ag₂SO₄. The measured densities and refractive indices of these highly colored glasses were converted to molar volumes and molar refractivities. Comparison of the partial molar volumes and refractivities with those of alkali germanate glasses suggests the Tl⁺ and Ag⁺ are about as effective in causing the transformation of GeO₄ tetrahedra to GeO₆ octahedra as are K⁺ and Na⁺. The presence of intense color with Tl⁺ and Ag⁺ is related to their stronger polarizabilities and polarizing power compared to the rare‐gas‐type alkali ions. The onset of color at 15 mole % Tl₂O and 4 mole % Ag₂O may be related to a change of bonding from ionic to covalent for Tl⁺. This conclusion agrees with recent NMR findings for thallium borate glasses.