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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Three-dimensional superconductivity induced by an extremely small amount of Li in Li x ⁢SnSe 2

Unconventional superconductivity occurs often in materials with low dimensionality. Furthermore, we report superconductivity observed in layered Li x SnSe 2 with the superconducting transition temperature T c ~ 6 K. Through L⁢i + intercalation in semiconducting SnSe 2 via electrochemical process, Li x ⁢SnSe 2 is formed with an extremely small x value as estimated from the c-axis lattice parameter, carrier concentration, and first-principles calculations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Local Sn Dipolar-Character Displacements behind the Low Thermal Conductivity in SnSe Thermoelectric

The local atomic structure of SnSe was characterized across its orthorhmbic-to-orthorhombic structural phase transition using x-ray pair distribution function analysis. Substantial Sn displacements with a dipolar character persist in the high symmetry high temperature phase, albeit with a symmetry different from that of the ordered displacements below the transition. The analysis implies that the transition is neither order-disorder nor displacive, but rather a complex crossover. Robust ferro-coupled SnSe intra-layer distortions suggest a ferroelectric-like instability as the driving force. Furthermore, these local symmetry-lowering Sn displacements are likely integral to the ultra-low lattice thermal conductivity mechanism in SnSe.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SnSe by Materials Project

SnSe crystallizes in the orthorhombic Cmcm space group. The structure is two-dimensional and consists of two SnSe sheets oriented in the (0, 1, 0) direction. Sn2+ is bonded to five equivalent Se2- atoms to form a mixture of corner and edge-sharing SnSe5 square pyramids. There are one shorter (2.74 Å) and four longer (3.04 Å) Sn–Se bond lengths. Se2- is bonded to five equivalent Sn2+ atoms to form a mixture of corner and edge-sharing SeSn5 square pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SnSe by Materials Project

SnSe crystallizes in the orthorhombic Cmcm space group. The structure is two-dimensional and consists of two SnSe sheets oriented in the (0, 1, 0) direction. Sn2+ is bonded in a rectangular see-saw-like geometry to four equivalent Se2- atoms. There are two shorter (2.76 Å) and two longer (3.06 Å) Sn–Se bond lengths. Se2- is bonded in a rectangular see-saw-like geometry to four equivalent Sn2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SnSe by Materials Project

SnSe crystallizes in the orthorhombic Pnma space group. The structure is two-dimensional and consists of two SnSe sheets oriented in the (0, 0, 1) direction. Sn2+ is bonded in a 5-coordinate geometry to three equivalent Se2- atoms. There are one shorter (2.78 Å) and two longer (2.84 Å) Sn–Se bond lengths. Se2- is bonded in a 3-coordinate geometry to three equivalent Sn2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SnSe by Materials Project

SnSe crystallizes in the tetragonal P4/nmm space group. The structure is two-dimensional and consists of one SnSe sheet oriented in the (0, 0, 1) direction. Sn2+ is bonded to five equivalent Se2- atoms to form a mixture of edge and corner-sharing SnSe5 square pyramids. There are one shorter (2.72 Å) and four longer (3.06 Å) Sn–Se bond lengths. Se2- is bonded in a single-bond geometry to five equivalent Sn2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SnSe by Materials Project

SnSe crystallizes in the orthorhombic Pmmn space group. The structure is one-dimensional and consists of two SnSe ribbons oriented in the (0, 1, 0) direction. Sn2+ is bonded in a T-shaped geometry to three equivalent Se2- atoms. There are one shorter (2.77 Å) and two longer (2.91 Å) Sn–Se bond lengths. Se2- is bonded in a 3-coordinate geometry to three equivalent Sn2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SnSe by Materials Project

SnSe crystallizes in the orthorhombic Pnma space group. The structure is two-dimensional and consists of two SnSe sheets oriented in the (0, 0, 1) direction. Sn2+ is bonded to five equivalent Se2- atoms to form a mixture of corner and edge-sharing SnSe5 square pyramids. There are a spread of Sn–Se bond distances ranging from 2.74–3.05 Å. Se2- is bonded to five equivalent Sn2+ atoms to form a mixture of corner and edge-sharing SeSn5 square pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SnSe by Materials Project

SnSe crystallizes in the orthorhombic Cmcm space group. The structure is one-dimensional and consists of four SnSe ribbons oriented in the (1, 0, 0) direction. Sn2+ is bonded in a bent 120 degrees geometry to two equivalent Se2- atoms. There are one shorter (2.58 Å) and one longer (2.59 Å) Sn–Se bond lengths. Se2- is bonded in a linear geometry to two equivalent Sn2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2024

High Mobility, High Carrier Density SnSe 2 Field‐Effect Transistors with Ultralow Subthreshold Swing and Gate‐Controlled Photoconductance Switching

2D and layered semiconductors are considered as promising electronic materials, particularly for applications that require high carrier mobility and efficient field-effect switching combined with mechanical flexibility. To date, however, the highest mobility has been realized primarily at low carrier concentration. Here, it is shown that few-layer/multilayer SnSe 2 gated by a solution top gate combines very high room-temperature electron mobility (up to 800 cm 2 V −1 s −1 ), along with large on-off current ratios (>10 5 ) and a subthreshold swing below the thermodynamic limit (50 mV per decade) in field-effect devices, at exceptionally large sheet carrier concentrations of ≈10 13 cm −2 . Observed mobility enhancements upon partial depletion of the channel point to near-surface defects or impurities as the mobility-limiting scattering centers. Under illumination, the resulting gap states give rise to gate-controlled switching between positive and negative photoconductance. The results qualify SnSe 2 as a promising layered semiconductor for flexible and wearable electronics, as well as for the realization of advanced approaches to photodetection.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Linear Dichroism of the Optical Properties of SnS and SnSe Van der Waals Crystals

Abstract Tin monochalcogenides SnS and SnSe, belonging to a family of Van der Waals crystals isoelectronic to black phosphorus, are known as environmentally friendly materials promising for thermoelectric conversion applications. However, they exhibit other desired functionalities, such as intrinsic linear dichroism of the optical and electronic properties originating from strongly anisotropic orthorhombic crystal structures. This property makes them perfect candidates for polarization‐sensitive photodetectors working in near‐infrared spectral range. A comprehensive study of the SnS and SnSe crystals is presented, performed by means of optical spectroscopy and photoemission spectroscopy, supported by ab initio calculations. The studies reveal the high sensitivity of the optical response of both materials to the incident light polarization, which is interpreted in terms of the electronic band dispersion and orbital composition of the electronic bands, dictating the selection rules. From the photoemission investigation the ionization potential, electron affinity and work function are determined, which are parameters crucial for the design of devices based on semiconductor heterostructures.

Chemistry↗
DOE OSTI2020

Materials Data on SnSe by Materials Project

SnSe is Halite, Rock Salt structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Sn2+ is bonded to six equivalent Se2- atoms to form a mixture of corner and edge-sharing SnSe6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Sn–Se bond lengths are 3.03 Å. Se2- is bonded to six equivalent Sn2+ atoms to form a mixture of corner and edge-sharing SeSn6 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Co2(SnSe)3 by Materials Project

Co2(SnSe)3 is Hausmannite-derived structured and crystallizes in the trigonal R-3 space group. The structure is three-dimensional. there are two inequivalent Co sites. In the first Co site, Co is bonded to three Sn and three Se atoms to form CoSn3Se3 octahedra that share corners with six CoSn3Se3 octahedra, corners with four equivalent SnCo2Se2 tetrahedra, and corners with four equivalent SeCo2Sn2 tetrahedra. The corner-sharing octahedra tilt angles range from 51–56°. There are a spread of Co–Sn bond distances ranging from 2.51–2.54 Å. There are one shorter (2.39 Å) and two longer (2.42 Å) Co–Se bond lengths. In the second Co site, Co is bonded to three equivalent Sn and three equivalent Se atoms to form corner-sharing CoSn3Se3 octahedra. The corner-sharing octahedra tilt angles range from 51–56°. All Co–Sn bond lengths are 2.52 Å. All Co–Se bond lengths are 2.40 Å. There are two inequivalent Sn sites. In the first Sn site, Sn is bonded to two Co and two equivalent Se atoms to form distorted SnCo2Se2 tetrahedra that share corners with four equivalent CoSn3Se3 octahedra, corners with two equivalent SnCo2Se2 tetrahedra, corners with four equivalent SeCo2Sn2 tetrahedra, and an edgeedge with one SnCo2Se2 tetrahedra. The corner-sharing octahedra tilt angles range from 69–74°. There are one shorter (2.75 Å) and one longer (2.94 Å) Sn–Se bond lengths. In the second Sn site, Sn is bonded in a 4-coordinate geometry to two equivalent Co and two equivalent Se atoms. There are one shorter (2.76 Å) and one longer (2.93 Å) Sn–Se bond lengths. There are two inequivalent Se sites. In the first Se site, Se is bonded in a 4-coordinate geometry to two equivalent Co and two equivalent Sn atoms. In the second Se site, Se is bonded to two Co and two equivalent Sn atoms to form distorted SeCo2Sn2 tetrahedra that share corners with four equivalent CoSn3Se3 octahedra, corners with two equivalent SeCo2Sn2 tetrahedra, corners with four equivalent SnCo2Se2 tetrahedra, and an edgeedge with one SeCo2Sn2 tetrahedra. The corner-sharing octahedra tilt angles range from 68–75°.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Suppressing Charged Cation Antisites via Se Vapor Annealing Enables p-Type Dopability in AgBiSe 2 –SnSe Thermoelectrics

Cation disordering is commonly found in multinary cubic compounds, but its effect on electronic properties has been neglected because of difficulties in determining the ordered structure and defect energetics. An absence of rational understanding of the point defects present has led to poor reproducibility and uncontrolled conduction type. AgBiSe 2 is a representative compound that suffers from poor reproducibility of thermoelectric properties, while the origins of its intrinsic n-type conductivity remain speculative. Here, it is demonstrated that cation disordering is facilitated by Bi Ag charged antisite defects in cubic AgBiSe 2 which also act as a principal donor defect that greatly controls the electronic properties. Using density functional theory calculations and in situ Raman spectroscopy, how saturation annealing with selenium vapor can stabilize p-type conductivity in cubic AgBiSe 2 alloyed with SnSe at high temperatures is elucidated. With stable and controlled hole concentration, a peak is observed in the weighted mobility and the density-of-states effective mass in AgBiSnSe 3 , implying an increased valley degeneracy in this system. These findings corroborate the importance of considering the defect energetics for exploring the dopability of ternary thermoelectric chalcogenides and engineering electronic bands by controlling self-doping.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Microscopic Manipulation of Ferroelectric Domains in SnSe Monolayers at Room Temperature

Two-dimensional (2D) van der Waals ferroelectrics provide an unprecedented architectural freedom for the creation of artificial multiferroics and nonvolatile electronic devices based on vertical and coplanar heterojunctions of 2D ferroic materials. Nevertheless, controlled microscopic manipulation of ferroelectric domains is still rare in monolayer-thick 2D ferroelectrics with in-plane polarization. Here we report the discovery of robust ferroelectricity with a critical temperature close to 400 K in SnSe monolayer plates grown on graphene and the demonstration of controlled room-temperature ferroelectric domain manipulation by applying appropriate bias voltage pulses to the tip of a scanning tunneling microscope (STM). This study shows that STM is a powerful tool for detecting and manipulating the microscopic domain structures in 2D ferroelectric monolayers, which are difficult for conventional approaches such as piezoresponse force microscopy, thus facilitating the hunt for other 2D ferroelectric monolayers with in-plane polarization with important technological applications.

2D ferroelectric↗
DOE OSTI2020

Extended anharmonic collapse of phonon dispersions in SnS and SnSe

The lattice dynamics and high-temperature structural transition in SnS and SnSe are investigated via inelastic neutron scattering, high-resolution Raman spectroscopy and anharmonic first-principles simulations. We uncover a spectacular, extreme softening and reconstruction of an entire manifold of low-energy acoustic and optic branches across a structural transition, reflecting strong directionality in bonding strength and anharmonicity. Further, our results solve a prior controversy by revealing the soft-mode mechanism of the phase transition that impacts thermal transport and thermoelectric efficiency. Our simulations of anharmonic phonon renormalization go beyond low-order perturbation theory and capture these striking effects, showing that the large phonon shifts directly affect the thermal conductivity by altering both the phonon scattering phase space and the group velocities. These results provide a detailed microscopic understanding of phase stability and thermal transport in technologically important materials, providing further insights on ways to control phonon propagation in thermoelectrics, photovoltaics, and other materials requiring thermal management.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Photoinduced anisotropic lattice dynamic response and domain formation in thermoelectric SnSe

Identifying and understanding the mechanisms behind strong phonon–phonon scattering in condensed matter systems is critical to maximizing the efficiency of thermoelectric devices. To date, the leading method to address this has been to meticulously survey the full phonon dispersion of the material in order to isolate modes with anomalously large linewidth and temperature-dependence. Here we combine quantitative MeV ultrafast electron diffraction (UED) analysis with Monte Carlo based dynamic diffraction simulation and first-principles calculations to directly unveil the soft, anharmonic lattice distortions of model thermoelectric material SnSe. A small single-crystal sample is photoexcited with ultrafast optical pulses and the soft, anharmonic lattice distortions are isolated using MeV-UED as those associated with long relaxation time and large displacements. We reveal that these modes have interlayer shear strain character, induced mainly by c -axis atomic displacements, resulting in domain formation in the transient state. These findings provide an innovative approach to identify mechanisms for ultralow and anisotropic thermal conductivity and a promising route to optimizing thermoelectric devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗