Some are different from others: high temperature structural phase transitions in ternary chalcopyrites

The high temperature behaviour of AIBIIIX2VI chalcopyrites (A = Cu; B = Al, Ga und In; X = S, Se, Te) was studied by in‐situ high temperature synchrotron radiation X‐ray diffraction. Structural phase transitions from the α phase with chalcopyrite structure to the β phase with sphalerite structure were obtained in the compounds CuInX2 and CuGaTe2. The driving force of this order‐disorder transition is a Cu–In anti site occupancy starting in the critcal temperature region, nearly 10 K before the transition temperature. The order parameter of the phase transition, expressed as Δn e = |n e (disordered) – n e (ordered)|, goes within the critical region to zero according to |T – T trans|β with the critical exponent β = 0.35(7). Structural transitions were also obtained in CuAlTe2 and CuGaSe2, but they show a different character. In the first compound it goes with the occurrence of a small two phases region, in the second with the formation of an other, unknown phase. Furthermore neither critical behaviour nor an anti site occupancy of the cations is observed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)