In-situ investigation of the structural phase transition in kesterite

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Abstract

A polycrystalline Cu2ZnSnS4 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 Iequation image2m) to the cubic sphalerite type structure (space group Fequation image3m). 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 acub. 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 Cu2ZnSnS4 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 Iequation image2m) is not a subgroup of Iequation image2d) and a group-subgroup relation is mandatory for displacive phase transitions, the non-existence of a Iequation image2m) → Iequation image2d) transition seems plausible. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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