The local structure of crystalline Ge8Sb2Te 11 over a temperature range from 10 K to 480 K was studied. While a rhombohedral to rock-salt-like structural transition is clearly observed at 385 K via x ray (Bragg) diffraction, an x-ray absorption study shows that the local structure associated with the rhombohedral configuration at 10 K, where six Ge(Sb)-Te bonds are split into three shorter and three longer bonds, remains unchanged across the transition temperature, Tc. Based upon a fit of the experimental data to a correlated Einstein model, the shorter Sb-Te bond was found to be stiffer than its Ge-Te counterpart. Using DFT calculations, a tendency for the shorter bonds to localize around vacancies was noted, clearly displaying an increase in static disorder in Ge-Sb-Te alloys with respect to pure GeTe. This increase in static disorder may be directly related to the decrease in Tc observed when GeTe is alloyed with Sb 2Te3. Total energy calculations found the coupling of Sb-Te and a vacancy to be energetically the most favorable in Ge-Sb-Te compounds, where vacancies serve to buffer internal stresses caused by the Sb-Te bonds.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - 2011 Sep 7|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics