Structural transition on doping rare earth Sm to Ge2Sb2Te5 phase change material

Abstract

The effect of doping rare earth element Sm on the structure of Ge2Sb2Te5 (GST) phase change material is studied. The X-ray diffraction (XRD) spectra of (Ge2Sb2Te5)100−xSmx(x = 0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2) bulk alloys are analyzed to understand the impact of Sm doping. The Rietveld refinement of XRD results discloses the change in lattice parameters of the hexagonal phase of GST on Sm doping whereas no significant change in the fcc phase is observed. The quantitative phase analysis of GST with Sm doping is analyzed and the fraction of hexagonal phase shows an increase, while the fraction of the fcc phase reduces up to x = 0.4% Sm addition. The crystallite size and strain of GST obtained using the WH-plot increases with Sm content up to x = 0.4%. There is an increase in d103-spacing of the hexagonal phase on Sm incorporation. The change in the local structure of GST on Sm addition is studied employing Raman Spectroscopy and Far-IR spectroscopy. The local structure around Ge and Sb is observed to change as there is an increase in the fraction of octahedral Ge in comparison to the tetrahedral Ge with Sm content from x = 0 to x = 0.4 . This results in the lowering of homopolar Ge—Ge and Ge—Sb bonds due to the decrease in Ge rich tetrahedra from x = 0 to x = 0.4 of Sm addition.