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11 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Ge2Sb2Te5 by Materials Project

Ge2Sb2Te5 is MAX Phase-like structured and crystallizes in the trigonal P-3m1 space group. The structure is two-dimensional and consists of one Ge2Sb2Te5 sheet oriented in the (0, 0, 1) direction. Ge4+ is bonded to six Te2- atoms to form GeTe6 octahedra that share corners with three equivalent SbTe6 octahedra, edges with three equivalent SbTe6 octahedra, and edges with six equivalent GeTe6 octahedra. The corner-sharing octahedral tilt angles are 6°. There are three shorter (2.84 Å) and three longer (3.30 Å) Ge–Te bond lengths. Sb1+ is bonded to six Te2- atoms to form SbTe6 octahedra that share corners with three equivalent GeTe6 octahedra, corners with three equivalent SbTe6 octahedra, edges with three equivalent GeTe6 octahedra, and edges with nine equivalent SbTe6 octahedra. The corner-sharing octahedra tilt angles range from 0–6°. There are three shorter (3.02 Å) and three longer (3.19 Å) Sb–Te bond lengths. There are three inequivalent Te2- sites. In the first Te2- site, Te2- is bonded to six equivalent Sb1+ atoms to form TeSb6 octahedra that share corners with six equivalent TeGe3Sb3 octahedra and edges with twelve TeSb6 octahedra. The corner-sharing octahedral tilt angles are 4°. In the second Te2- site, Te2- is bonded to three equivalent Ge4+ and three equivalent Sb1+ atoms to form a mixture of edge and corner-sharing TeGe3Sb3 octahedra. The corner-sharing octahedral tilt angles are 4°. In the third Te2- site, Te2- is bonded in a 3-coordinate geometry to three equivalent Ge4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ge2Sb2Te5 by Materials Project

Ge2Sb2Te5 is Caswellsilverite-like structured and crystallizes in the trigonal P-3m1 space group. The structure is two-dimensional and consists of one Ge2Sb2Te5 sheet oriented in the (0, 0, 1) direction. Ge4+ is bonded to six Te2- atoms to form GeTe6 octahedra that share corners with three equivalent GeTe6 octahedra, corners with three equivalent SbTe6 octahedra, edges with three equivalent SbTe6 octahedra, and edges with nine equivalent GeTe6 octahedra. The corner-sharing octahedra tilt angles range from 0–5°. There are three shorter (3.00 Å) and three longer (3.04 Å) Ge–Te bond lengths. Sb1+ is bonded to six Te2- atoms to form SbTe6 octahedra that share corners with three equivalent GeTe6 octahedra, edges with three equivalent GeTe6 octahedra, and edges with six equivalent SbTe6 octahedra. The corner-sharing octahedral tilt angles are 5°. There are three shorter (3.01 Å) and three longer (3.20 Å) Sb–Te bond lengths. There are three inequivalent Te2- sites. In the first Te2- site, Te2- is bonded to six equivalent Ge4+ atoms to form TeGe6 octahedra that share corners with six equivalent TeGe3Sb3 octahedra and edges with twelve TeGe6 octahedra. The corner-sharing octahedral tilt angles are 1°. In the second Te2- site, Te2- is bonded to three equivalent Ge4+ and three equivalent Sb1+ atoms to form a mixture of edge and corner-sharing TeGe3Sb3 octahedra. The corner-sharing octahedral tilt angles are 1°. In the third Te2- site, Te2- is bonded in a 6-coordinate geometry to three equivalent Sb1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ge2Sb2Te5 by Materials Project

Ge2Sb2Te5 crystallizes in the monoclinic Cm space group. The structure is three-dimensional. there are two inequivalent Ge4+ sites. In the first Ge4+ site, Ge4+ is bonded to six Te2- atoms to form GeTe6 octahedra that share corners with two SbTe6 octahedra, corners with three GeTe6 octahedra, edges with three equivalent GeTe6 octahedra, and edges with six SbTe6 octahedra. The corner-sharing octahedra tilt angles range from 2–7°. There are a spread of Ge–Te bond distances ranging from 2.85–3.20 Å. In the second Ge4+ site, Ge4+ is bonded to six Te2- atoms to form GeTe6 octahedra that share corners with two SbTe6 octahedra, corners with three GeTe6 octahedra, edges with three equivalent GeTe6 octahedra, and edges with six SbTe6 octahedra. The corner-sharing octahedra tilt angles range from 1–4°. There are a spread of Ge–Te bond distances ranging from 2.82–3.19 Å. There are two inequivalent Sb1+ sites. In the first Sb1+ site, Sb1+ is bonded to six Te2- atoms to form SbTe6 octahedra that share corners with two GeTe6 octahedra, corners with three SbTe6 octahedra, edges with three equivalent SbTe6 octahedra, and edges with six GeTe6 octahedra. The corner-sharing octahedra tilt angles range from 0–8°. There are a spread of Sb–Te bond distances ranging from 2.98–3.20 Å. In the second Sb1+ site, Sb1+ is bonded to six Te2- atoms to form SbTe6 octahedra that share corners with two GeTe6 octahedra, corners with three SbTe6 octahedra, edges with three equivalent SbTe6 octahedra, and edges with six GeTe6 octahedra. The corner-sharing octahedra tilt angles range from 0–4°. There are a spread of Sb–Te bond distances ranging from 2.95–3.19 Å. There are five inequivalent Te2- sites. In the first Te2- site, Te2- is bonded to two Ge4+ and three Sb1+ atoms to form TeGe2Sb3 square pyramids that share corners with six TeGe2Sb3 square pyramids and edges with seven TeGe3Sb2 square pyramids. In the second Te2- site, Te2- is bonded in a rectangular see-saw-like geometry to two Ge4+ and two Sb1+ atoms. In the third Te2- site, Te2- is bonded to three Ge4+ and two Sb1+ atoms to form TeGe3Sb2 square pyramids that share corners with six TeGe3Sb2 square pyramids and edges with seven TeGe2Sb3 square pyramids. In the fourth Te2- site, Te2- is bonded to three Ge4+ and two Sb1+ atoms to form a mixture of corner and edge-sharing TeGe3Sb2 square pyramids. In the fifth Te2- site, Te2- is bonded to two Ge4+ and three Sb1+ atoms to form a mixture of corner and edge-sharing TeGe2Sb3 square pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2023

In situ investigation of ion irradiation-induced amorphization of (Ge 2 Sb 2 Te 5 ) 1−x C x [0 ≤ x ≤ 0.12]

Chalcogenide thin films that undergo reversible phase changes show promise for use in next-generation nanophotonics, microelectronics, and other emerging technologies. One of the many studied compounds, Ge2Sb2Te5, has demonstrated several useful properties and performance characteristics. However, the efficacy of benchmark Ge2Sb2Te5 is restricted by amorphous phase thermal stability below ∼150 °C, limiting its potential use in high-temperature applications. In response, previous studies have added a fourth species (e.g., C) to sputter-deposited Ge2Sb2Te5, demonstrating improved thermal stability. Our current research confirms reported thermal stability enhancements and assesses the effects of carbon on crystalline phase radiation response. Through in situ transmission electron microscope irradiation studies, we examine the effect of C addition on the amorphization behavior of initially cubic and trigonal polycrystalline films irradiated using 2.8 MeV Au to various doses up to 1 × 1015 cm −2 . It was found that increased C content reduces radiation tolerance of both cubic and trigonal phases.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Octahedral to tetrahedral bonding transitions in the local structure of phase change optical media Ge 2 Sb 2 Se 5 x Te 5-5 x with Se doping

Random access memories utilize fast, reversible switching between ordered and disordered states of matter in phase change materials (PCMs) such as Ge2Sb2Te5-5x. The short-range structure in the disordered phase has been described either as (i) a network of Ge tetrahedra or (ii) Peierls distorted Ge/Sb octahedra. The PCM transition was investigated in bulk Ge2Sb2Se5xTe5-5x (GSST), in which amorphization sets in with Se doping (x ≈ 0.85) upon quenching. GSST has a hexagonal crystalline ground state with Ge/Sb octahedral coordination, but the phase change transition to the amorphous state that is only observed when the system is quenched brings a short-range structure with sharp, tetrahedrally coordinated Ge/Sb correlations and shortened bonds that are distinctly different from the expected octahedral pairing.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2024

Chalcogenide phase-change material advances programmable terahertz metamaterials: a non-volatile perspective for reconfigurable intelligent surfaces

Terahertz (THz) waves have gained considerable attention in the rising 6G communication due to their large bandwidth. However, the cost and power consumption become the major constraints for the commercialization of 6G THz systems as the frequency increases. Reconfigurable intelligent surface (RIS) comprising active metasurfaces and digital controllers has been proposed for beamforming in the 6G multiple-input-multiple-output systems, showing good potential to suppress the system size, weight, and power consumption (SWaP). Currently, their controlling diodes can hardly work up to THz frequencies. Therefore, several active stimuli have been investigated as alternatives. Among them, chalcogenide phase-change material Ge 2 Sb 2 Te 5 (GST) addresses large modulation depth, picosecond switching speed, and non-volatile properties. Notably, the non-volatile GST may enable RIS systems with memory and low control power. This work briefly reviews the advances of GST-tuned THz metamaterials (MTMs), discusses the current obstacles to overcome, and gives a perspective of GST applications in the rising 6G communications.

6G↗