Cu₁₂Sb₄S₁₃: A Temperature-Dependent Structure Investigation

Synthetic tetrahedrite, Cu₁₂Sb₄S₁₃, obtained by reaction of the elements, has been investigated at various temperatures in the 295-573 K range. It crystallizes in the cubic system with a = 10.3293 (6) Å, V = 1102.1 (2) Å³, space group I3m and Z = 2 at room temperature. The structure refinement converged to a residue of R = 0.0165 (at room temperature, wR = 0.0200) for 389 independent reflections and 34 refined parameters. A Gram-Charlier non-harmonic development of the atomic displacement factor for both independent Cu atoms was used. The results show a disorder for the three-coordinated Cu atom, within and perpendicular to the plane of the three surrounding S atoms. However, although the non-harmonic probability density deformation increases with raising the temperature within this plane, it barely changes in the perpendicular direction. This suggests two different types of disorder: static in-plane and dynamic out-of-plane, therefore underlining a possible diffusion pathway for copper ions. To check the significance of the observed effects, the errors for the one-particle potentials and the probability density function maps were calculated by means of a Monte-Carlo method.

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