scholarly journals Carrier concentration dependence of structural disorder in thermoelectric Sn1−xTe

IUCrJ ◽  
2016 ◽  
Vol 3 (5) ◽  
pp. 377-388 ◽  
Author(s):  
Mattia Sist ◽  
Ellen Marie Jensen Hedegaard ◽  
Sebastian Christensen ◽  
Niels Bindzus ◽  
Karl Frederik Færch Fischer ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Low Temperature ◽  
Rock Salt ◽  
Theoretical Calculations ◽  
Rhombohedral Phase ◽  
Structural Disorder ◽  
Entropy Method ◽  
Salt Crystal ◽  
X Ray ◽  
Two Samples

SnTe is a promising thermoelectric and topological insulator material. Here, the presumably simple rock salt crystal structure of SnTe is studied comprehensively by means of high-resolution synchrotron single-crystal and powder X-ray diffraction from 20 to 800 K. Two samples with different carrier concentrations (sampleA= high, sampleB= low) have remarkably different atomic displacement parameters, especially at low temperatures. Both samples contain significant numbers of cation vacancies (1–2%) and ordering of Sn vacancies possibly occurs on warming, as corroborated by the appearance of multiple phases and strain above 400 K. The possible presence of disorder and anharmonicity is investigated in view of the low thermal conductivity of SnTe. Refinement of anharmonic Gram–Charlier parameters reveals marginal anharmonicity for sampleA, whereas sampleBexhibits anharmonic effects even at low temperature. For both samples, no indications are found of a low-temperature rhombohedral phase. Maximum entropy method (MEM) calculations are carried out, including nuclear-weighted X-ray MEM calculations (NXMEM). The atomic electron densities are spherical for sampleA, whereas for sampleBthe Te electron density is elongated along the 〈100〉 direction, with the maximum being displaced from the lattice position at higher temperatures. Overall, the crystal structure of SnTe is found to be defective and sample-dependent, and therefore theoretical calculations of perfect rock salt structures are not expected to predict the properties of real materials.

Crystal structure of potassium tetraperoxomolybdate (VI) K2[Mo(O2)4]

2005 ◽  
Vol 20 (3) ◽  
pp. 203-206 ◽  
Author(s):  
M. Grzywa ◽  
M. Różycka ◽  
W. Łasocha
Keyword(s):  
Crystal Structure ◽  
Low Temperature ◽  
Diffraction Pattern ◽  
Powder Diffraction ◽  
Rietveld Method ◽  
Structure Refinement ◽  
Crystal Structure Refinement ◽  
Unit Cell Parameters ◽  
X Ray ◽  
Cell Parameters

Potassium tetraperoxomolybdate (VI) K2[Mo(O2)4] was prepared, and its X-ray powder diffraction pattern was recorded at low temperature (258 K). The unit cell parameters were refined to a=10.7891(2) Å, α=64.925(3)°, space group R−3c (167), Z=6. The compound is isostructural with potassium tetraperoxotungstate (VI) K2[W(O2)4] (Stomberg, 1988). The sample of K2[Mo(O2)4] was characterized by analytical investigations, and the results of crystal structure refinement by Rietveld method are presented; final RP and RWP are 9.79% and 12.37%, respectively.

Crystal structure, thermodynamic properties and detonation characterization of bis(5-amino-1,2,4-triazol-3-yl)methane

2020 ◽  
Vol 76 (1) ◽  
pp. 64-68 ◽  
Author(s):  
Hongya Li ◽  
Biao Yan ◽  
Haixia Ma ◽  
Zhiyong Sun ◽  
Yajun Ma ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Detonation Velocity ◽  
Theoretical Calculations ◽  
Detonation Pressure ◽  
X Ray Diffraction ◽  
X Ray ◽  
Equivalent Equation ◽  
Experimental Values ◽  
Experimental Density

Bis(5-amino-1,2,4-triazol-3-yl)methane (BATZM, C5H8N8) was synthesized and its crystal structure characterized by single-crystal X-ray diffraction; it belongs to the space group Fdd2 (orthorhombic) with Z = 8. The structure of BATZM can be described as a V-shaped molecule with reasonable chemical geometry and no disorder. The specific molar heat capacity (Cp,m ) of BATZM was determined using the continuous Cp mode of a microcalorimeter and theoretical calculations, and the Cp,m value is 211.19 J K−1 mol−1 at 298.15 K. The relative deviations between the theoretical and experimental values of Cp,m , HT – H 298.15K and ST – S 298.15K of BATZM are almost equivalent at each temperature. The detonation velocity (D) and detonation pressure (P) of BATZM were estimated using the nitrogen equivalent equation according to the experimental density; BATZM has a higher detonation velocity (7954.87 ± 3.29 m s−1) and detonation pressure (25.72 ± 0.03 GPa) than TNT.

π-Olefin-Iridium-Komplexe, XXII [1]. C-H-Aktivierung von aromatischen und aliphatischen Solvensmolekülen RH bei der Reaktion von [Cp*IrCI2]2 mit Butadienmagnesium unter Bildung von [Cp*Ir(η3-C4H7)R] sowie Kristallstruktur von [Cp*Ir(η3-C4H7)C6H5] / π-Olefin Iridium Complexes, XXII [1]. C-H Activation of Aromatic and Aliphatic Solvent Molecules RH in the Reaction of [Cp*IrCl2]2 with Butadienemagnesium with Formation of [Cp*Ir(η3-C4H7)R], and Crystal Structure of [Cp*Ir(η3-C4H7)C6H5]

1994 ◽  
Vol 49 (12) ◽  
pp. 1645-1653 ◽  
Author(s):  
Jörn Müller ◽  
Petra Escarpa Gaede ◽  
Ke Qiao
Keyword(s):  
Crystal Structure ◽  
Low Temperature ◽  
Diffraction Analysis ◽  
Iridium Complexes ◽  
X Ray Diffraction ◽  
X Ray ◽  
Nmr Spectrometry ◽  
Benzene Toluene ◽  
Solvent Molecules ◽  
Mechanism Of The Reaction

Reactions of [Cp*IrCl2]2 (Cp*=η3-C5Me5) with [MgC4H6·2 THF]n at low temperature give [Cp*Ir(η4-C4H6)] together with [Cp*Ir(η3-C4H7)R] compounds, the latter being formed via C-H activation of solvent molecules RH (RH = benzene, toluene, anisole, thiophene, furane, N-methylpyrrole, pentane, cyclohexane. THF). In the case of pyrrole, C-N -activation occurs. The ratio of syn and anti isomers of the 1-methylallyl complexes as well as the sites of C-H activation of RH were investigated by NMR spectrometry. An enantiomorphous crystal of [Cp*Ir(η3-C4H7)C6Hs] was characterized by X-ray diffraction analysis which reveals trigonal planar coordination at the Ir atom and an exo, syn conformation of the 1-methylallyl ligand. A mechanism of the reaction which involves 16-electron intermediates is discussed. The corresponding system [Cp*RhCl2]2/butadienemagnesium/RH gives only [Cp*Rh(η4-C4H6)], and no C-H activation is observed.

Benzo-18-krone-6 -Acetonitril (1/2): Kristallisation und Tieftemperatur- Röntgenstrukturanalyse / Benzo-18 -crown-6 -Acetonitrile (1/2): Crystallization and Low-Temperature X-Ray Analysis

1998 ◽  
Vol 53 (12) ◽  
pp. 1528-1530 ◽  
Author(s):  
Karna Wijaya ◽  
Oliver Moers ◽  
Armand Blaschette ◽  
Peter G. Jones
Keyword(s):  
Crystal Structure ◽  
Low Temperature ◽  
Data Collection ◽  
Single Crystals ◽  
Title Complex ◽  
Monoclinic Space Group ◽  
Hydrogen Atoms ◽  
Space Group ◽  
X Ray ◽  
Mecn Solution

Abstract Benzo-18 -crown-6 -Acetonitrile (1/2), Crystal Structure Single crystals of the title complex resulted fortuitously during an attempt to co-crystallise MeN(SO2Me)2 with benzo-18-crown-6 from an MeCN solution at -30 °C. The crystal structure has been determined via data collection at -100 °C (monoclinic, space group P21/n, Z = 4). The nitrile molecules are located with their me­ thyl groups above and below the plane of the 18-membered crown ring, the Me hydrogen atoms being rotationally disordered about the MeCN axes; C(methyl)···O(crown) distances range from 309.4(3) to 384.9(3) pm.

Aragonite-type lanthanum orthoborate, LaBO3

2006 ◽  
Vol 62 (4) ◽  
pp. i103-i105 ◽  
Author(s):  
Akihiko Nakatsuka ◽  
Osamu Ohtaka ◽  
Hiroshi Arima ◽  
Noriaki Nakayama ◽  
Tadato Mizota
Keyword(s):  
Crystal Structure ◽  
Low Temperature ◽  
Single Crystal ◽  
General Position ◽  
Type Structure ◽  
Space Group ◽  
X Ray ◽  
Thermal Vibrations

The crystal structure of the low-temperature (LT) modification of LaBO3 has been redetermined from single-crystal X-ray data; the resulting structure confirms the previous study [Abdullaev, Dzhafarov & Mamedov (1976). Azerbaidzhanskii Khim. Zh. pp. 117–120], but with improved precision. LT-LaBO3 crystallizes in space group Pnma and adopts the aragonite-type structure. Except for one O atom, which is situated on a general position, all other atoms (one La, one B and a second O atom) lie on mirror planes. The structure is composed of LaO9 polyhedra with an average La—O distance of 2.593 Å and trigonal BO3 groups with an average B—O distance of 1.373 Å. Slight anisotropies of the thermal vibrations of La and B atoms suggest that the electrostatic La...La and La...B interactions across the shared edges are weak.

SURFACE PHONONS OF THE (100) SURFACE OF SOME COMPOUNDS WITH A ROCK-SALT CRYSTAL STRUCTURE

1991 ◽  
Vol 05 (05) ◽  
pp. 381-389 ◽  
Author(s):  
CHUHEI OSHIMA
Keyword(s):  
Crystal Structure ◽  
Rock Salt ◽  
Dispersion Curves ◽  
Shielding Effect ◽  
Transition Metal Carbide ◽  
Free Electrons ◽  
Salt Crystal ◽  
Dynamical Parameters ◽  
Surface Phonons ◽  
Electron Energy Loss

The energy dispersion curves of surface phonons of the (100) surface of some compounds with a rock-salt crystal structure (TiC, ZrC, HfC, NbC, TaC, MgO, and NiO) have been investigated using electron energy loss spectroscopy. Drastic changes in force constants on all the carbide surfaces are correlated with a rippled structure. On the other hand, the surface phonons of insulating compounds, NiO and MgO (100), have showed dispersion curves agreeing with the predicted ones calculated on the basis of a shell model with bulk dynamical parameters. No changes in the parameters near the NiO and MgO (100) surfaces have been detected. The shielding effect of free electrons on the surface phonon for the transition metal carbide surfaces is discussed.

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