The results obtained for the isothermal crystallization for bi3 Te17 Se80 thin films have been used to determine the expression for phase transformation rate for a non-isothermal regime. This formalism enables one to determine the apparant energies of the growth rate and nucleation rate. The results show that a temperature range exists where the heterogeneous crystallization is preponderant and for higher temperatures the crystallization becomes homogenous with crystallites of size greater than the film thickness. The apparant activation energy for nucleation EN is 1.09eV while for growth Ev is 0.55eV.