The tracer diffusivities of Na-22 and Ca-45 in two high-quality silica glasses produced by the Deutsche Glastechnische Gesellschaft as standard glasses I and II have been measured in the temperature range between 473 K and 783 K. The temperature dependences of the tracer diffusion coefficients in both glasses follow Arrhenius laws. The diffusion of Na-22 is more than six orders of magnitude faster than the diffusion of Ca-45. The ionic conductivity was determined by frequency-dependent impedance spectroscopy and the conductivity diffusion coefficient D-sigma was deduced from the do conductivity via the Nernst-Einstein relation. The temperature dependences of D, for both glasses follow also Arrhenius functions. The activation parameters and pre-exponential factors for tracer diffusion and for conductivity diffusion were determined. The activation enthalpy of Na-22 and the activation enthalpy of the do conductivity are equal, showing that the conductivity of standard glasses is due to the motion of Na ions. The viscosity diffusivities D-eta were determined from available viscosity data using the Stokes-Einstein relation. They are considerably slower than both tracer diffusivities. The Haven ratios H-R are temperature independent for both glasses. The diffusivities of Na-22 and 45Ca in soda-lime glasses increase with increasing Na2O content. (c) 2006 Elsevier B.V. All rights reserved.