The impurity diffusion parameters of Zn, Co and Ni have been determined in aluminium by measurements of electrical resistance. I t is shown experimentally that in the case of Co and Ni, surface layers with constant concentrations were formed during the isothermal diffusion treatments and so the resistance memurements made possible the determination of the temperature dependence of the saturation concentrations too. It is also shown that the determination of the diffusion activation energy is possible from resistance measurements when the initial and boundary conditions are not exactly known (but when they do not vary with temperature). The measurements gave for the pre-exponential factors (Do) and the energies of activation (Q) : DOZn = (0.20 f 0.08) cm8/s, QZn= (1.25 f 0.02) eV ; DOC"= (141 f 137) cm*/s, Qco = (1.75 0.07) eV ; DoNi = (4.4 f 3.1) cm5/s, Q"= (1.51 f 0.06) eV, respectively. The diffusion parameters of Zn and Co are in good agreement with previous results in the literature : no data on the impurity diffusion coefficients of Ni in aluminium have as yet been published.I n the interpretation of experimental results it has been concluded that the energy differences calculated from the Le Claire model (Le Claire 1962) disagree with AQexp=Qi-Qself, even in those cmes when the phase-shift method, used in the calculation of the excess potential around the impurities, gave better resistivity values than those obtained from the resonant scattering condition. The method of Neumann and Hirschwald (1973) also gives much smaller A Q values than those determined experimentally. A possible interpretation of the discrepancies between the experimental and theoretical results is suggested by supposing that not only inpurity-vacancy pairs but higher-order complexes, i.e. two-impurity-vacancy triplets are also formed and play an important role in the diffusion of transition metal impurities. $1. INTRODUCTION As was pointed out by Ceresara, Federighi and Pieragostini (1966) the resistometric method (without sectioning of the specimen) can be valuable tool in a number of diffusion problems. To show this they investigated radial diffusion by measuring the resistance of a wire covered by the diffusing metal after subsequent annealing at constant temperature and calculated the function where Ro, R ( t ) and R, are the resistance at the beginning, after annealing for time t, and at t = CQ, respectively. In order to obtain the diffusion coefficient, D, the radial diffusion equation was solved with initial and boundary conditions corresponding to an instantaneous source, i.e. at the surface at t = 0. 2 H 2 Downloaded by [University of California Santa Barbara] at 22:41 14 June 2016 446 G. Erdblyi et al. These solutions c j i . s . (~) ( T = Dt/a2 where a is the radius of the cylinder), suitable for direct comparison with experimental data, were tabulated by Ceresara et al. (1966) for several values of the parameter y, defined by R, -Ro y=-=--, Po 8 0where (Y is the resistivity increase due to 1 at.% impurity, po the resistivity...