X-ray study of the modulated structure In quenched Ga_2Te_3 with a defect zinc-blende lattice

摘要

Ga_2Te_3 crystallizes into the zinc-blende structure, where one-third of the cation sites are vacant. Single-crystal X-ray diffraction studies have been performed on quenched Ga_2Te-3 crystals. The diffraction maps show, apart from the main zinc-blende-type reflections, satellite reflections at q = (0.060.060.00)_c, where the subscript c indicates the cubic sublattice. Analysis of the satellite reflections shows that the incommensurate structure is two-dimensional. The structure is ascribable to the amplitude-type modulation caused by Ga vacancies and the coupled displacive modulation of Te atoms, which has a polarization vector along the _c direction. The nature of the atomic modulations is also discussed and the origin of the modulation is attributed to Jahn-Teller-type distortions around Ga vacancies.