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13 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Li(TiSe2)3 by Materials Project

Li(TiSe2)2TiSe2 crystallizes in the trigonal P-3m1 space group. The structure is two-dimensional and consists of one Li(TiSe2)2 sheet oriented in the (0, 0, 1) direction and one TiSe2 sheet oriented in the (0, 0, 1) direction. In the Li(TiSe2)2 sheet, Li1+ is bonded to six equivalent Se2- atoms to form LiSe6 octahedra that share corners with twelve equivalent TiSe6 octahedra, edges with six equivalent LiSe6 octahedra, and faces with two equivalent TiSe6 octahedra. The corner-sharing octahedral tilt angles are 46°. All Li–Se bond lengths are 2.69 Å. Ti+3.67+ is bonded to six Se2- atoms to form TiSe6 octahedra that share corners with six equivalent LiSe6 octahedra, edges with six equivalent TiSe6 octahedra, and a faceface with one LiSe6 octahedra. The corner-sharing octahedral tilt angles are 46°. There are three shorter (2.55 Å) and three longer (2.61 Å) Ti–Se bond lengths. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to three equivalent Li1+ and three equivalent Ti+3.67+ atoms to form a mixture of distorted edge and corner-sharing SeLi3Ti3 pentagonal pyramids. In the second Se2- site, Se2- is bonded in a distorted T-shaped geometry to three equivalent Ti+3.67+ atoms. In the TiSe2 sheet, Ti+3.67+ is bonded to six equivalent Se2- atoms to form edge-sharing TiSe6 octahedra. All Ti–Se bond lengths are 2.57 Å. Se2- is bonded in a distorted T-shaped geometry to three equivalent Ti+3.67+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Materials Data on TiSe2 by Materials Project

TiSe2 is trigonal omega structured and crystallizes in the trigonal P-3m1 space group. The structure is two-dimensional and consists of one TiSe2 sheet oriented in the (0, 0, 1) direction. Ti4+ is bonded to six equivalent Se2- atoms to form edge-sharing TiSe6 octahedra. All Ti–Se bond lengths are 2.57 Å. Se2- is bonded in a distorted T-shaped geometry to three equivalent Ti4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LiTiSe2O by Materials Project

Li2O2(TiSe2)2 is Hydrophilite-derived structured and crystallizes in the trigonal P3m1 space group. The structure is two-dimensional and consists of three Li2O2 sheets oriented in the (0, 0, 1) direction and three TiSe2 sheets oriented in the (0, 0, 1) direction. In each Li2O2 sheet, Li1+ is bonded in a trigonal planar geometry to three equivalent O2- atoms. All Li–O bond lengths are 2.01 Å. O2- is bonded in a trigonal planar geometry to three equivalent Li1+ atoms. In each TiSe2 sheet, Ti4+ is bonded to six Se+1.50- atoms to form edge-sharing TiSe6 octahedra. There are three shorter (2.54 Å) and three longer (2.56 Å) Ti–Se bond lengths. There are two inequivalent Se+1.50- sites. In the first Se+1.50- site, Se+1.50- is bonded in a 3-coordinate geometry to three equivalent Ti4+ atoms. In the second Se+1.50- site, Se+1.50- is bonded in a 3-coordinate geometry to three equivalent Ti4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf(Ti2Se5)2 by Materials Project

HfSe2(TiSe2)4 is trigonal omega-derived structured and crystallizes in the monoclinic C2/m space group. The structure is two-dimensional and consists of one HfSe2 sheet oriented in the (0, 0, 1) direction and four TiSe2 sheets oriented in the (0, 0, 1) direction. In the HfSe2 sheet, Hf4+ is bonded to six equivalent Se2- atoms to form edge-sharing HfSe6 octahedra. All Hf–Se bond lengths are 2.65 Å. Se2- is bonded in a distorted T-shaped geometry to three equivalent Hf4+ atoms. In each TiSe2 sheet, Ti4+ is bonded to six Se2- atoms to form edge-sharing TiSe6 octahedra. There are a spread of Ti–Se bond distances ranging from 2.56–2.61 Å. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a distorted T-shaped geometry to three equivalent Ti4+ atoms. In the second Se2- site, Se2- is bonded in a distorted T-shaped geometry to three equivalent Ti4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LiTi(SeO)2 by Materials Project

LiO2TiSe2 crystallizes in the monoclinic C2/m space group. The structure is two-dimensional and consists of one LiO2 sheet oriented in the (0, 0, 1) direction and one TiSe2 sheet oriented in the (0, 0, 1) direction. In the LiO2 sheet, Li is bonded in a distorted hexagonal planar geometry to six equivalent O atoms. There are two shorter (2.07 Å) and four longer (2.09 Å) Li–O bond lengths. O is bonded in a trigonal non-coplanar geometry to three equivalent Li atoms. In the TiSe2 sheet, Ti is bonded to six equivalent Se atoms to form edge-sharing TiSe6 octahedra. All Ti–Se bond lengths are 2.55 Å. Se is bonded in a distorted T-shaped geometry to three equivalent Ti atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Symmetry-mode analysis for local structure investigations using pair distribution function data

Symmetry-adapted distortion modes provide a natural way of describing distorted structures derived from higher-symmetry parent phases. Structural refinements using symmetry-mode amplitudes as fit variables have been used for at least ten years in Rietveld refinements of the average crystal structure from diffraction data; more recently, this approach has also been used for investigations of the local structure using real-space pair distribution function (PDF) data. Here, the value of performing symmetry-mode fits to PDF data is further demonstrated through the successful application of this method to two topical materials: TiSe2, where a subtle but long-range structural distortion driven by the formation of a charge-density wave is detected, and MnTe, where a large but highly localized structural distortion is characterized in terms of symmetry-lowering displacements of the Te atoms. Here, the analysis is performed using fully open-source code within the DiffPy framework via two packages developed for this work: isopydistort, which provides a scriptable interface to the ISODISTORT web application for group theoretical calculations, and isopytools, which converts the ISODISTORT output into a DiffPy-compatible format for subsequent fitting and analysis. These developments expand the potential impact of symmetry-adapted PDF analysis by enabling high-throughput analysis and removing the need for any commercial software.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Photon-induced selenium migration in TiSe 2

TiSe 2 is a member of the transition metal dichalcogenide family of layered van der Waals materials which exhibits some distinct electronic and optical properties. Here, in this work, we perform Raman spectroscopy and microscopy studies on single crystal TiSe 2 to investigate thermal and photon-induced defects associated with diffusion of selenium to the surface. Additional phonon peaks near 250 cm -1 are observed in the laser-irradiated regions that are consistent with formation of amorphous and nanocrystalline selenium on the surface. Temperature dependent studies of the threshold temperature and laser intensity necessary to initiate selenium migration to the surface show an activation barrier for the process of 1.55 eV. The impact of these results on the properties of strongly correlated electron states in TiSe 2 are discussed

36 MATERIALS SCIENCE↗
DOE OSTI2019

Comment on “Chiral Phase Transition in Charge Ordered 1 T - TiSe 2 ”

A previous report of the emergence of chirality for the ( 2 × 2 × 2 ) charge density wave (CDW) in TiSe 2 has attracted much interest; the drastic symmetry breaking is highly unusual with few precedents. In that study, key evidence was provided by x-ray diffraction measurements of two superlattice reflections, (1.5 1.5 0.5) and (2.5 1 0). The (2.5 1 0) reflection appeared to show an anomalously large intensity and a transition onset at ~7 K below that of the (1.5 1.5 0.5) reflection. These observations, aided by modeling, were cited as evidence for a separate chiral transition. Here, we show that the prior conclusions based on x-ray diffraction are erroneous. There is just one transition, and it is achiral.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Ab Initio Theory of Unconventional Superconductivity [Poster]

This is an overview of the Quasiparticle Self-Consistent GW Approximation (QSGW) with the following: (1) Origins of Superconductivity in FeSe, (2) Properties of YFe 2 Ge 2 , (3) Dynamical Mean Field Theory: for strong local correlations, and (4) is TiSe 2 an excitonic insulator?

42 ENGINEERING↗