GRAIN-BOUNDARY DIFFUSION AND GRAIN-BOUNDARY SEGREGATION OF TELLURIUM IN SILVER

Using the radiotracers 121Te and Te-123 with high specific activity, g rain boundary (GB) diffusion of Te in Ag has been studied in a wide te mperature interval of about 600 K. At low temperatures (378-504 K) Har rison's type-C regime has been realized, which has enabled us to perfo rm a number of direct measurements of the GB diffusion (GBD) coefficie nt D(GB). The activation energy and the preexponential factor of GBD a re equal to H(GB) = 86.75 kJ/mol and D(GB)0 = 1.01 x 10(-4) m2/s, resp ectively. Combining the obtained D(GB)-values with the P = sD(GB)delta -values measured at higher temperatures (650-970 K) in the B-regime, t he GB-segregation factor s has been estimated taking the GB width of d elta = 0.5 nm. The resultant s-values predict an enthalpy of GB-segreg ation of H(s) congruent-to -43.29 kJ/mol. This is the first study with C-regime measurements of impurity GBD and accurate estimations of the GB-segregation factor from the GBD-data. Comparing the present result s with the results of our recent C-regime measurements of GB self-diff usion in silver [J. appl. Phys. 72, 2758 (1992)], a possibility of 2D- phase formation during Te GBD in Ag is discussed.