Structural change of crystalline and amorphous-Ge(2)Sb(2)Te(5) by reverse Monte Carlo analysis of x-ray diffraction data and extended x-ray absorption fine structure data.

Reverse Monte Carlo analyses of crystalline and amorphous Ge(2)Sb(2)Te(5) thin films were carried out using x-ray diffraction data and three spectra from extended x-ray absorption fine structure measurements. To produce a crystal model, we employed a large system with 12 800 Ge, 12 800 Sb and 32 000 Te atoms. The obtained model for the crystal structure was used for the initial configuration of the amorphous model. As a result of a series of reverse Monte Carlo analyses with various constraints, we found that the partial pair distribution function in the amorphous state with the largest deviation from the crystal state is a Ge-Sb pair and the distance is less than 2.7 Å. This suggests that Sb atoms in amorphous Ge(2)Sb(2)Te(5) thin film have a four-coordinate within 3.2 Å.