Self-Diffusion in Solid Krypton

An isotropic exchange apparatus has been developed and used to measure tracer diffusion in solid krypton in the temperature region 90<T<115^∘K. The crystals of krypton were grown from the melt in a cell with a conical bottom and annealed carefully before use. While the crystals could not be examined in situ for physical perfection, the reproducibility of the diffusion results from specimen to specimen indicates that the crystals contained few gross imperfections. For some of the crystals, the diffusion could be described within the experimental uncertainty by the simple Arrhenius expression D=D₀e^-Q/RT, but for others Q showed a temperature dependence. The addition of O₂ appeared to depress D over the entire temperature range studied. The magnitude of these results in relation to those for pure krypton suggests that the temperature dependence of Q may be caused by impurities. If the observed Q at the highest temperature (4800±{}200 cal mole^-1) is interpreted in terms of intrinsic diffusion via single vacancies and decomposed into an energy of formation (1780±{}200 cal mole^-1) and an energy for mobility, the ratio of the energies EᵥEₘ turns out to be appreciably smaller than has been estimated theoretically.