Tracer diffusion and ionic conduction in standard silica glasses

The tracer diffusivities of (22)Na and (45)Ca in two high-quality standard silica glasses have been measured in the temperature range between 473 and 783 K. The temperature dependences of the tracer diffusion coefficients in both glasses follow Arrhenius laws. The diffusion of (22)Na is six to seven orders of magnitude faster than the diffusion Of (45)Ca. The ionic conductivity was determined by impedance spectroscopy and the conductivity diffusion coefficient D(sigma) was deduced from the dc conductivity via the Nernst-Einstein relation. The temperature dependences of D(sigma) 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 (22)Na diffusion is almost equal to the activation enthalpy of the dc conductivity. We conclude that the conductivity of standard glasses is due to the motion of Na ions. The diffusivities of (22)Na and (45)Ca in soda-lime glasses increase with increasing Na(2)O content.