skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: NMR study of vacancy and structure-induced changes in Cu 2-x Te

Authors:
; ; ;
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1413388
Grant/Contract Number:
SC-0008574
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Journal of Physics and Chemistry of Solids
Additional Journal Information:
Journal Volume: 106; Journal Issue: C; Related Information: CHORUS Timestamp: 2017-12-14 19:05:13; Journal ID: ISSN 0022-3697
Publisher:
Elsevier
Country of Publication:
United Kingdom
Language:
English

Citation Formats

Sirusi, Ali A., Page, Alexander, Uher, Ctirad, and Ross, Jr., Joseph H.. NMR study of vacancy and structure-induced changes in Cu 2-x Te. United Kingdom: N. p., 2017. Web. doi:10.1016/j.jpcs.2017.02.016.
Sirusi, Ali A., Page, Alexander, Uher, Ctirad, & Ross, Jr., Joseph H.. NMR study of vacancy and structure-induced changes in Cu 2-x Te. United Kingdom. doi:10.1016/j.jpcs.2017.02.016.
Sirusi, Ali A., Page, Alexander, Uher, Ctirad, and Ross, Jr., Joseph H.. Sat . "NMR study of vacancy and structure-induced changes in Cu 2-x Te". United Kingdom. doi:10.1016/j.jpcs.2017.02.016.
@article{osti_1413388,
title = {NMR study of vacancy and structure-induced changes in Cu 2-x Te},
author = {Sirusi, Ali A. and Page, Alexander and Uher, Ctirad and Ross, Jr., Joseph H.},
abstractNote = {},
doi = {10.1016/j.jpcs.2017.02.016},
journal = {Journal of Physics and Chemistry of Solids},
number = C,
volume = 106,
place = {United Kingdom},
year = {Sat Jul 01 00:00:00 EDT 2017},
month = {Sat Jul 01 00:00:00 EDT 2017}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1016/j.jpcs.2017.02.016

Citation Metrics:
Cited by: 2works
Citation information provided by
Web of Science

Save / Share:
  • The commensurate superstructures of a NiAs/Ni{sub 2}In type parent structure, Ni{sub 3.32}InTe{sub 2} and Ni{sub 3.12}In{sub 0.86}Te{sub 2.14} (q={gamma}[0 0 1]{sup *}, {gamma}=2/3) as well as one dimensionally incommensurate structure of Ni{sub 3}InTe{sub 2} ({gamma}=0.71) were refined from neutron powder diffraction data (R{sub wp}=4.77%, 4.53% and 4.91% for the three structures, respectively, at 298 K). The commensurate structures were refined in the P6{sub 3}/mmc space group (c=3c{sub NiAs}). The stacking sequence at the hcp array is -In/Te/Te/- and the trigonal bipyramidal site within the In layer, Ni(2), is partially occupied while it is empty in the Te layers. The octahedralmore » position in between the In and Te layers, Ni(1a), is fully occupied while the octahedral position in between two adjacent Te layers, Ni(1b), is partially occupied. With decreasing In and Ni content, the modulation wave vector, {gamma}, was found to increase continuously until {gamma}=1. From this, crenel functions to describe the whole homogeneity range of the solid solution were constructed with the length of the atomic domains {delta}{sup Te}={gamma} (and hence {delta}{sup In}={delta}{sup Ni}=1-{gamma}) and {delta}{sup Ni(1b)}={gamma}/2 (and hence {delta}{sup Ni(1a)}=1-{gamma}/2) which were then used for the refinement of the incommensurate structure of Ni{sub 3}InTe{sub 2}. The corresponding effect in real space is that the single In layers separating double layers of Te occur less frequent when {gamma} in increasing until at {gamma}=1 the CdI{sub 2} type structure of Ni{sub 1+x}Te{sub 2} is reached. - Graphical abstract: The crystal structure of Ni{sub 3.31}InTe{sub 2} is a superstructure of the NiAs type structure with q={gamma}[0 0 1]{sup *}, {gamma}=2/3. The -In/Te/Te/- stacking sequence at the hcp array can be described with a crenel function with the length of the atomic domains {delta}{sup Te}={gamma} and {delta}{sup In}=1-{gamma}. With decreasing In and Ni content, the modulation wave vector, {gamma}, increases continuously until {gamma}=1. The corresponding effect in real space is that the In layers separating double layers of Te occur less frequently until at {gamma}=1 the CdI{sub 2} type structure of Ni{sub 1+x}Te{sub 2} is reached.« less
  • A gradual uncontrollable increase in the resistivity of the amorphous phase of phase-change alloys, such as Ge{sub 2}Sb{sub 2}Te{sub 5}, known as drift, is a serious technological issue for application of phase-change memory. While it has been proposed that drift is related to structural relaxation, no direct structural results have been reported so far. Here, we report the results of Ge L{sub 3}-edge x-ray absorption measurements that suggest that the drift in electrical conductivity is associated with the gradual conversion of tetrahedrally coordinated Ge sites into pyramidal sites, while the system still remains in the amorphous phase. Based on electronicmore » configuration arguments, we propose that during this process, which is governed by the existence of lone-pair electrons, the concentration of free carriers in the system decreases resulting in an increase in resistance despite the structural relaxation towards the crystalline phase.« less
  • The seleno- and tellurothallate(I) anions Tl{sub 2}CH{sub 2}{sup 2{minus}} (Ch = Se and/or Te) and the {sup 77}Se-enriched Tl{sub 2}Se{sub 2}{sup 2{minus}} anion have been obtained by extraction of the alloys MTlCh (M = Na, K; Ch = Se, Te), KTlSe{sub 0.5}Te{sub 0.5}, and {sup 77}Se-enriched KTlSe in ethylenediamine and liquid NH{sub 3} and in the presence of a stoichiometric excess of 2,2,2-crypt with respect to M{sup +}. The butterfly-shaped Tl{sub 2}Ch{sub 2}{sup 2{minus}} anions were characterized in solution by {sup 77}Se, {sup 203}Tl, and {sup 205}Tl NMR spectroscopy, Raman spectroscopy, and X-ray crystallography in (2,2,2-crypt-K{sup +}){sub 2}Tl{sub 2}Ch{sub 2}{supmore » 2{minus}}. The energy-minimized structures of the Tl{sub 2}Ch{sub 2}{sup 2{minus}} (Ch = Se and/or Te) anions were calculated by using density functional theory calculations confirming the nonplanar geometries of all three anions, which are compared with those of the presently unknown In{sub 2}Ch{sub 2}{sup 2{minus}} (Ch = Se, Te) anions. The magnitudes of the relativistically corrected reduced coupling constants, (K{sub Tl-Ch}){sub RC}, are consistent with essentially pure p-bonded rings whereas the magnitudes of (K{sub Tl-Tl}){sub RC} suggest significant s electron density along the Tl{hor_ellipsis}Tl axes and is confirmed by theory. Density functional theory calculations were also used to assign the solid-state vibrational spectra of Tl{sub 2}Se{sub 2}{sup 2{minus}} and Tl{sub 2}Te{sub 2}{sup 2{minus}}. The variation of the {sup 205}Tl-{sup 203}Tl spin-spin coupling constants with solvent and temperature, the differences between the calculated and experimentally determined fold angles, and the low experimental and calculated vibrational frequencies of the anion deformation modes indicate that the anion geometries are significantly influenced by environmental factors.« less
  • The Rh-Te and Ir-Te binary systems for 50--78 atom% Te show remarkable differences in their phase and structural features at temperatures below 1,100 C. Extended Hueckel calculations are employed to investigate the influence of various orbital interactions on these differences. In general, a strong interrelationship among valence electron count, orbital characteristics at and near the Fermi levels, and relative strengths of M-Te, Te-Te, and M-M orbital interactions control the occurrence and structures of various M{sub x}Te{sub 2} compounds (0.75 {le} x {le} 2). Stronger Ir-Te than Rh-Te orbital interactions lead to the different low-temperature structures of IrTe{sub 2} (CdI{sub 2}-type)more » and RhTe{sub 2} (pyrite-type), but then short and intermediate-range Te-Te interactions lead to the pyrite-type structure for the defect phases M{sub 1{minus}u}Te{sub 2}. At temperatures above 600 C, RhTe{sub 2} (pyrite-type) is unstable relative to disproportionation to the stuffed CdI{sub 2}-type Rh{sub 1+x}Te{sub 2} and the defect pyrite-type Rh{sub 1{minus}u}Te{sub 2}. The Rh-rich phases, Rh{sub 1+x}Te{sub 2}, show ordered vacancies in alternating layers of octahedral holes and can be formulated as (Rh{sub 3}){sub x}(Rh){sub 1{minus}2x}Te{sub 2} (x {le} {1/2}) and (Rh{sub 3}){sub 1{minus}x}(Rh){sub 4x{minus}2}Te{sub 2} (x {ge} {1/2}) to emphasize the occurrence of linear Rh{sub 3} units in their structures. The pattern of vacancies in these structures follows the preference of Rh{sub 4n+3} oligomers over Rh{sub 4n+1} chains. Charge-iterative calculations of Rh atomic orbital energies in Rh{sub 1+x}Te{sub 2} (x = 0.0, 0.5, 1.0) were carried out to analyze the electronic properties of Rh throughout the series. As x increases, Rh-Te orbital interactions become less attractive and the concentration of Rh-Rh repulsive interactions grows. Both effects control the maximum value of x (observed to be 0.84) for this series and influence the pattern of occupied octahedral holes in the close-packed tellurium matrix.« less
  • Potassium (K) plays an essential role in promoting catalytic reaction in many established industrial catalytic processes. Here, we report a combined study using scanning tunneling microscopy (STM) and density functional theory (DFT) in understanding the effect of depositing K on the atomic and electronic structures as well as chemical activities of Cu xO/Cu(111) (x≤2). The DFT calculations observe a pseudomorphic growth of K on Cu xO/Cu(111) up to 0.19 monolayer (ML) of coverage, where K binds the surface via strong ionic interaction with chemisorbed oxygen and the relatively weak electrostatic interactions with copper ions, lower and upper oxygen on themore » Cu xO rings. The simulated STM pattern based on the DFT results agrees well with the experimental observations. The deposited K displays great impact on the surface electronic structure of Cu xO/Cu(111), which induces significant reduction in work function and leads to a strong electron polarization on the surface. The promotion of K on the surface binding properties is selective. It varies depending on the nature of adsorbates. According to our results, K has little effect on surface acidity, while it enhances the surface basicity significantly. As a consequence, the presence of K does not help for CO adsorption on Cu xO/Cu(111), but being able to accelerate the activation of CO 2. Thus, such promotion strongly depends on the combinations from both geometric and electronic effects. Our results highlight the origin of promoting effect of alkalis in the design of catalysts for the complex reactions.« less