A study of highly symmetrical crystal structures, commonly seen in high-speed phase-change materials, using synchrotron radiation

The crystal structures of phase-change materials, GeTe-Sb2Te3 and Ag-In-Sb-Te compounds, crystallized by laser irradiation, have been investigated for several years. These investigations revealed that these two compounds crystallize into a single phase with a cubic or a pseudo-cubic structure as the structural unit, and that their constituent atoms tend to randomly occupy the lattice sites. This time, the structure of Au25Ge4Sn11Te60 has been investigated using a large Debye-Sherrer camera installed in BL02B2 at SPring-8. This compound crystallizes into a single phase like the others do, and its crystal has a simple cubic structure with atoms of Au, Ge, Sn or Te randomly occupying the I(a) site in the Pm (3) over barm space group. A cubic structure is isotropic in symmetry. The characteristics commonly seen in these high-speed phase-change materials, i.e. crystallization into a single phase, isotropic symmetry, and random occupation, suggest that atomic migration length becomes so short that crystallization is completed very rapidly. This means that the time taken to erase a record can be markedly shortened.