(GeTe)nSbInTe3 (n≤3)—Element distribution and thermal behavior

• The new compounds 21R-GeSbInTe4, 9P-Ge2SbInTe5 and 33R-Ge3SbInTe are described.
• The element distribution in 33R-Ge3SbInTe6 was determined by resonant scattering.
• The cation concentration in the crystal structure is strongly modulated.
• The Sb substitution by In has a significant impact on phase transitions.
• Results may be relevant for thermoelectrics and thin-film phase-change materials.

Antimony in germanium antimony tellurides (GeTe)n(Sb2Te3) can be substituted by indium. Homogeneous bulk samples of GeSbInTe4 (R3̄m, Z=3, a=4.21324(5) Å, c=41.0348(10) Å) and Ge2SbInTe5 (P3̄m1, Z=1, a=4.20204(6) Å, c=17.2076(4) Å) were obtained; their structures were refined with the Rietveld method. Single-crystal X-ray diffraction using synchrotron radiation at the K edges of Sb and Te (exploiting anomalous dispersion) yields precise information on the element distribution in the trigonal layered structure of Ge3SbInTe6 (R3̄m, Z=3, a=4.19789(4) Å, c=62.1620(11) Å). The structure is characterized by van der Waals gaps between distorted rocksalt-type slabs of alternating cation and anion layers. The cation concentration is commensurately modulated with Sb preferring the positions near the gaps. In contrast to unsubstituted Ge3Sb2Te6, quenching the NaCl-type high-temperature phase (stable above ~510 °C) easily yields a pseudocubic modification that is metastable at ambient conditions. Temperature-dependent powder diffraction reveals a broader stability range of the cubic high-temperature modification of Ge3SbInTe6 compared to the ternary phases. In-containing samples partially decompose at ca. 300 °C but become homogeneous again when the high-temperature phase is formed.

Crystal structure of 33R-Ge3SbInTe6 as determined by resonant X-ray diffraction, one example of the (GeTe)nSbInTe3 series of compounds investigated.Figure optionsDownload as PowerPoint slide