• copper;
  • aluminosilicates;
  • glass;
  • thermal expansion;
  • X-ray

The local environment around copper in the Cu2O·Al2O3·4SiO3 and CuO·Al2O3·4SiO2 glasses was investigated using the extended X-ray absorption fine structure (EXAFS) technique. It has been found that each Cu(I) in the former glass is coordinated to two oxygens through covalent Cu(I)-O bonds. This is the primary reason for its low thermal expansion coefficient (∼10 × 10−7 K−1). In the latter glass, which was made by heating the former glass at 600°C in air, each Cu(II) is coordinated to four oxygens and the bonds are ionic in character, contributing to the increase in the thermal expansion coefficient to ∼30 × 10−7 K−1.