Polytypism in the cation-deficient iron sulfide, ${\mathrm{Fe}}_9$${\mathrm{S}}_{10}$, and the magnetokinetics of the diffusion process at temperatures about the antiferro- to ferrimagnetic ($\lambda$) phase transition

The variation of the periodicity along the $C$ axis ($N^{\prime }C$) as a function of temperature in ${\mathrm{Fe}}_9$ ${\mathrm{S}}_{10}$, where $N^{\prime }$ varies between 5 and 1 over the range 300-600 K, has been investigated. The antiferromagnetic to ferrimagnetic ($\lambda$) phase transition is explained in terms of a vacancy rearrangement. Using absolute-reaction-rate theory and measurements of magnetization as a function of time at constant temperature around the $\lambda$ transition, coefficients of diffusion for iron atoms along the $C$ axis have been determined over the range 440 to 484 K and found to be ∼${10}^{-18\mathrm{}}$ ${\mathrm{cm}}^2$/sec. Appropriate mechanisms for the diffusion process are also considered.