In-situ investigation of the structural phase transition in kesterite

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 1 (4) over bar 2m) to the cubic sphalerite type structure (space group F (4) over bar 3m). Within 866-883 degrees 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 similar to 930 degrees 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 similar to 150 degrees 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 antisite occupancy of the cation substructure. Because the space group 1 (4) over bar 2m is not a subgroup of 1 (4) over bar 2d and a group-subgroup relation is mandatory for displacive phase transitions, the non-existence of a 1 (4) over bar 2m -> 1 (4) over bar 2d transition seems plausible. (c) 2009 WILEY-VCH Verlaq GmbH & Co. KGaA, Weinheim