A New Theoretical Formulation of Temperature Effect on Impurities Diffusion Coefficients in Molten Tellurium

The evolution of effective diffusion coefficients D-eff of 13 different impurities in molten tellurium versus temperature T was studied. A new hyperbolic expression D-eff = f(T) for these impurities was established for effective segregation coefficients K-eff << 1 and for temperatures within the range 730 degrees K-925 degrees K. Experimental values of K-eff determined by zone melting process were used to calculate a series of 4 effective diffusion coefficients D-eff. at four different temperatures, for each impurity. These experimental results of D-eff were fitted with the new expression of D-eff = f(T) to confirm its validity. The diffusion mechanism of 13 impurities at the solid-liquid interface was then investigated under our previous experimental conditions (velocity v of interface. the starting concentration CO, and number it of passes). These investigations confirmed that the temperature increase of tellurium molten zone was not convenient to reach an optimal purification by zone melting process.