Diffusion can take place through clusters of vacancies, such as divacancies, trivacancies etc., as long as the formation of these agglomerates is energetically feasible, as illustrated in Fig- 3. In thermal equilibrium, there is always a non-zero statistical probability that monovacancies meet and form divacancies. As temperature increases, the concentrations of both mono-and divacancies at equilibrium also rise. However, the concentration of divacancies increases statistically more rapidly, thus becoming significant at high temperatures. In addition, divacancies in fcc metals exhibit greater mobility than monovacancies. Consequently, self-diffusion in fcc metals generally involves contributions from both the monovacancy and divacancy mechanism. Apart from these differences, the two mechanisms strongly resemble each other. The influence of bound trivacancies on diffusion is usually considered negligible.