New insights on the GeSe _x Te_1−x phase diagram from theory and experiment

Abstract

The high-pressure and low-temperature behaviour of the GeSe x Te 1Àx system (x = 0, 0.2, 0.5, 0.75, 1) was studied using a combination of powder diffraction measurements and first-principles calculations. Compounds in the stability field of the GeTe structure type (x = 0, 0.2, 0.5) follow the high-pressure transition pathway: GeTe-I (R3m) ! GeTe-II (f.c.c.) ! GeTe-III (Pnma). The newly determined GeTe-III structure is isostructural to -GeSe, a high-pressure and high-temperature polymorph of GeSe. Pressure-dependent formation enthalpies and stability regimes of the GeSe x Te 1Àx polymorphs were studied by DFT calculations. Hexagonal Ge 4 Se 3 Te is stable up to at least 25 GPa. Significant differences in the high-pressure and low-temperature behaviour of the GeTetype structures and the hexagonal phase are highlighted. The role of GeÁ Á ÁGe interactions is elucidated using the crystal orbital Hamilton population method. Finally, a sketch of the high-pressure phase diagram of the system is provided.

Overcoming the Thermal Stability Limit of Chalcogenide Phase‐Change Materials for High‐Temperature Applications in GeSe1−xTex Thin Films

“…Both a c and V c continuously increase with x over the range (0.16–1) (Figure 4c,d). For x ≥ 0.48, the values of a c and V c in crystallized films are in close agreement with those measured on rhombohedral GeSe 1− x Te x bulk polycrystals, [ 19,20,23 ] In the study by Wiedemeier and Siemers, [ 19 ] the changes of a c and V c with x in bulk polycrystals with x ≥ 0.48 were fitted by linear laws. Thanks to the extension of the existence domain of the rhombohedral phase in thin films, we observe that the same trends continue down to x = 0.16.…”

“…In addition, in agreement with literature results, the crystallized GeSe film has an orthorhombic structure (see the Supporting Information). [20,30] The presence of a small amount of crystallized Ge is detected in most films, as expected from the resistivity curves (Figure 1). In summary, the crystallization of amorphous GeSe 1Àx Te x thin films leads to a rhombohedral phase from x ¼ 1 down to x ¼ 0.16.…”

“…[23]) Bulk (ref. [20]) Linear fit from ref. [19] Figure 4. a,b) XRD patterns of GeSe 1Àx Te x thin films crystallized by heating up to 400 C measured in the Bragg-Brentano geometry at room temperature.…”

“…www.advancedsciencenews.com www.pss-rapid.com on rhombohedral GeSe 1Àx Te x bulk polycrystals, [19,20,23] In the study by Wiedemeier and Siemers, [19] the changes of a c and V c with x in bulk polycrystals with x ≥ 0.48 were fitted by linear laws. Thanks to the extension of the existence domain of the rhombohedral phase in thin films, we observe that the same trends continue down to x ¼ 0.16.…”

“…[20]) Linear fit from ref. [19] Figure [19,20,23] In (d), the unit cell volume of the stable hexagonal phase for x between 0.1 and 0.45 is also reported. [19,21] The dashed lines in (c) and (d) are the linear laws accounting for the results in the study by Wiedemeier and Siemers.…”