Diffusion coefficient and heat of transport of H and D in niobium below room temperature

The diffusion coefficient and the heat of transport of H and D in Nb were determined by resistance measurements for concentrations between 0.01 and 0.15 at%. An activation energy of (0.123 ± 0.006) eV was measured for D in the whole temperature range investigated (150 to 320 K). For H a pronounced break in the Arrhenius plot was found at about 225 K in agreement with Gorsky effect measurements [1]. The activation energy changes from (0.093 ± 0.009) eV for T > 225 K to (0.061 ± 0.006) eV for T < 225 K. The ratio of the diffusion coefficients for H and D increases from two at room temperature to about 15 at 150 K. For temperatures between 200 and 320 K the heat of transport ranges between 0.09 and 0.15 eV for H and between 0.10 and 0.17 eV for D.