Abstract
A polycrystalline Cu~2~ZnSnS~4~ sample (kesterite) was investigated by in‐situ high temperature diffraction using synchrotron X‐rays, revealing for the first time a structural phase transition from the tetragonal kesterite type structure (space group I$ \bar 4 $2m) to the cubic sphalerite type structure (space group F$ \bar 4 $3m). Within 866–883 °C a phase transition region occurs, were a tetragonal phase and a cubic phase coexists. Outside the phase transition region, the lattice parameter of the tetragonal phase increase nearly linearly with increasing temperature, whereas the lattice parameter of the cubic phase show first a negative thermal expansion changing at ∼930 °C to a further linear increase of a~cub~. A cation anti‐site occupancy can only be observed within the phase transition region. On the other hand, the anion position parameters x and z change, which starts at ∼150 °C and lasts up to the phase transition region. Both atomic position parameters reach nearly the ideal value of 1/4, indicating the anion in the middle of the cation tetrahedra. Thus the structural phase transition in Cu~2~ZnSnS~4~ from the tetragonal kesterite type to the cubic sphalerite type structure is characterized much more by a displacive behaviour of the anion substructure then by an anti‐site occupancy of the cation substructure. Because the space group I$ \bar 4 $2m) is not a subgroup of I$ \bar 4 $2d) and a group‐subgroup relation is mandatory for displacive phase transitions, the non‐existence of a I$ \bar 4 $2m) → I$ \bar 4 $2d) transition seems plausible. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)