scholarly journals Features of the High-Temperature Structural Evolution of GeTe Thermoelectric Probed by Neutron and Synchrotron Powder Diffraction

Metals ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 48
Author(s):  
Javier Gainza ◽  
Federico Serrano-Sánchez ◽  
Norbert Marcel Nemes ◽  
José Luis Martínez ◽  
María Teresa Fernández-Díaz ◽  
...  
Keyword(s):  
Seebeck Coefficient ◽  
Powder Diffraction ◽  
Phonon Scattering ◽  
Thermal Evolution ◽  
Lone Pair ◽  
Structural Evolution ◽  
Rhombohedral Phase ◽  
Space Group ◽  
Synchrotron Powder Diffraction ◽  
Thermal Displacements

Among other chalcogenide thermoelectric materials, GeTe and derivative alloys are good candidates for intermediate temperature applications, as a replacement for toxic PbTe. We have prepared pure polycrystalline GeTe by using arc-melting, and investigated its structural evolution by using neutron powder diffraction (NPD) and synchrotron X-ray diffraction (SXRD), as well as its correlation with the thermal variation of the Seebeck coefficient. Besides a significant Ge deficiency (~7% Ge vacancies), the thermal evolution of the unit-cell volume and Ge-Te bond lengths in the rhombohedral phase (space group R3m), below 700 K, show unexpected anomalies involving the abrupt Ge-Te bond lengthening accompanied by increased Te thermal displacements. Above 700 K, the sample is cubic (space group Fm-3m) and shows considerably larger displacement parameters for Ge than for Te, as a consequence of the random distribution of the lone pair lobes of Ge2+. The Seebeck coefficient, reaching 120 μV K−1 at 775 K, shows a shoulder in the 500–570 K region that can be correlated to the structural anomaly, modifying the electron-phonon scattering in this temperature range.

scholarly journals Studying the structural and electronic effects of substituted (Bi0.5Na0.5)TiO3

2014 ◽  
Vol 70 (a1) ◽  
pp. C1522-C1522
Author(s):  
Peter Blanchard ◽  
Brendan Kennedy ◽  
Chris Ling
Keyword(s):  
Solid Solutions ◽  
Structural Changes ◽  
Structural Evolution ◽  
Rhombohedral Phase ◽  
Rhombohedral Structure ◽  
Electronic Effects ◽  
Spectra Analysis ◽  
Space Group ◽  
Industry Standard ◽  
Made In

Significant efforts have been made in the development of (Bi0.5Na0.5)TiO3 ferroelectrics as an alternative to the lead-based industry standard PbTi1-xZrxO3.[1] It has also been shown that doping the A- and B-site of (Bi0.5Na0.5)TiO3 can greatly improve the ferroelectric behavior of these materials,[2] possibly due to the formation of two or more ferroelectric phases at a morphotropic phase boundary (MPB). As such, there is a significant interest in understanding the structural changes in (Bi0.5Na0.5)TiO3-based solid solutions. (Bi0.5Na0.5)TiO3 was originally described as adopting a rhombohedral structure in space group R3c, However, the accuracy of this description has been greatly debated. It was recently suggested that (Bi0.5Na0.5)TiO3 actually adopts a monoclinic structure in space group Cc.[3] Given this recent controversy, we investigated the structural evolution of (Bi0.5Na0.5)TiO3-based solid solutions, particularly the (Bi0.5Na0.5)Ti1-xZrxO3 and (1-x)(Bi0.5Na0.5)TiO3–xBiFeO3 solid solutions., using both diffraction and spectroscopy techniques. Diffraction measurements on (Bi0.5Na0.5)TiO3 confirm that both monoclinic Cc and rhombohedral R3c phases are present at room temperature. Diffraction analysis showed that doping (Bi0.5Na0.5)TiO3 with a small amount of (Bi0.5Na0.5)ZrO3 and BiFeO3 can stabilizes the rhombohedral phase. The Ti/Fe K-edge and Zr L3-edge XANES spectra analysis was performed to determine the effects doping has on the local displacement of the B-site cations.

X-ray powder diffraction studies of (BaxSr1−x)2Co2Fe12O22 and (BaxSr1−x)Co2Fe16O27

2015 ◽  
Vol 30 (2) ◽  
pp. 139-148 ◽  
Author(s):  
W. Wong-Ng ◽  
G. Liu ◽  
Y. Yan ◽  
K. R. Talley ◽  
J. A. Kaduk
Keyword(s):  
Seebeck Coefficient ◽  
Powder Diffraction ◽  
Lattice Parameters ◽  
Hexagonal Ferrite ◽  
Layered Compounds ◽  
X Ray Diffraction ◽  
Powder Diffraction File ◽  
Space Group ◽  
X Ray ◽  
Diffraction Patterns

X-ray structural characterization and X-ray reference powder patterns have been determined for two series of iron- and cobalt-containing layered compounds (BaxSr1−x)2Co2Fe12O22 (x = 0.2, 0.4, 0.6, 0.8) and (BaxSr1−x)Co2Fe16O27 (x = 0.2, 0.4, 0.6, 0.8). The (BaxSr1−x)2Co2Fe12O22 series of compounds crystallized in the space group R$\bar 3$m (No. 166), with Z = 3. The structure is essentially that of the Y-type hexagonal ferrite, BaM2+Fe63+O11. The lattice parameters range from a = 5.859 15(8) to 5.843 72(8) Å, and c = 43.4975(9) to 43.3516(9) Å for x = 0.2 to 0.8, respectively. The (BaxSr1−x)Co2Fe16O27 series (W-type hexagonal ferrite) crystallized in the space group P63/mmc (No. 194) and Z = 2. The lattice parameters range from a = 5.902 05(12) to 5.8979(2) Å and c = 32.9002(10) to 32.8110(13) Å for x = 0.2 to 0.8. Results of measurements of the Seebeck coefficient and resistivity of these two sets of samples indicated that they are insulators. Powder X-ray diffraction patterns of these two series of compounds have been submitted to be included in the Powder Diffraction File.

Crystal structures of the relaxor oxide Pb2(ScTa)O6in the paraelectric and ferroelectric states

2002 ◽  
Vol 35 (2) ◽  
pp. 233-242 ◽  
Author(s):  
P. M. Woodward ◽  
K. Z. Baba-Kishi
Keyword(s):  
Powder Diffraction ◽  
Lone Pair ◽  
Domain Size ◽  
Group Symmetry ◽  
Coordination Polyhedra ◽  
Ferroelectric State ◽  
Space Group Symmetry ◽  
Space Group ◽  
Paraelectric State ◽  
Cooperative Ordering

The crystal structure of the relaxor ferroelectric Pb2ScTaO6has been refined from high-resolution neutron time-of-flight powder diffraction data recorded at various temperatures from 4 to 400 K. Upon warming, Pb2ScTaO6undergoes a first-order transition at 295 K from the rhombohedral ferroelectric state into the cubic paraelectric state. At 4.2 K, in the ferroelectric state, this compound adoptsR3 space-group symmetry, witha= 8.15231 (7) Å and α = 89.8488 (3)°. At 400 K, in the paraelectric state, this compound adoptsFm\bar{3}mspace-group symmetry, witha= 8.15345 (3) Å. In the ferroelectric state, the Pb2+coordination polyhedra are quite asymmetric, clearly indicating the presence of a stereoactive electron lone pair. The Sc3+and Ta5+ions are also shifted away from the centers of their respective octahedra, each toward an octahedral face. The large displacement parameters associated with both the Pb and the O ions, in the 400 K structure reveal significant local shifts of these ions from their ideal sites in the paraelectric state. Thus, the paraelectric to ferroelectric transition is driven by long-range cooperative ordering of the cation displacements. Synchrotron X-ray powder diffraction measurements are used to estimate the domain size of the Sc3+/Ta5+ordering and the ferroelectric cation displacements as 88 nm and 10 nm, respectively.

Revisiting the crystal structure of [Co(NH3)5Cl]Cl2 using synchrotron powder diffraction: to what extent single-crystal diffraction from 1960s got it right?

2017 ◽  
Vol 32 (3) ◽  
pp. 179-186 ◽  
Author(s):  
S. Mohamud ◽  
S. Pagola
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Powder Diffraction ◽  
Crystal Packing ◽  
Direct Methods ◽  
Rietveld Analysis ◽  
Single Crystal Diffraction ◽  
Space Group ◽  
Synchrotron Powder Diffraction ◽  
Structure Description

The crystal structure of the purpureo salt, [Co(NH3)5Cl]Cl2, first reported in 1963 and later revised in 1968 (in both cases from single-crystal diffraction) in the space group Pnma (No. 62), has been recently re-examined from synchrotron X-ray powder diffraction using direct methods and the software EXPO2013. The comparison of the Rietveld analysis results using the two published models and the atomic coordinates obtained from powders leads to an improved crystal structure description in the lower symmetry space group Pn21a (No. 33). As a result, the overall atom connectivity and crystal packing remain similar; however, the symmetry and internal geometry of the coordination complex are changed. The distortions from an idealized geometry in Pnma (No. 62) are likely because of energetically favorable hydrogen-bonding motifs in the crystal. The three models are compared, and their validity and limitations are discussed.

On two new K2FeF5 forms

2014 ◽  
Vol 29 (1) ◽  
pp. 33-41 ◽  
Author(s):  
Armel Le Bail
Keyword(s):  
Powder Diffraction ◽  
Thermal Evolution ◽  
Structural Type ◽  
Space Group ◽  
Type Space

Two additional forms of K2FeF5 are disclosed and characterized by powder diffraction. One (form-IV) adopts a new A2MF5 structural type, space group C2/m, a = 13.0919(2) Å, b = 5.7311(1) Å, c = 7.3114(1) Å, β = 118.241(1), and Z = 4, it is obtained from the thermal evolution of form-III, isostructural with Rb2FeF5, space group Pnma, a = 7.3964(2)  Å, b = 5.6779(1) Å, c = 11.5445(3) Å, and Z = 4. Both forms are compared to two previously reported polymorphs. The III → IV transition is topotactic, conserving the same zigzag cis-connected octahedral (FeF5)n2n− chains after an ~90° rotation and 1/2b translation of half of them.

Distorted chiolite crystal structures of α-Na5M3F14 (M=Cr,Fe,Ga) studied by X-ray powder diffraction

2003 ◽  
Vol 18 (2) ◽  
pp. 128-134 ◽  
Author(s):  
A. Le Bail ◽  
A.-M. Mercier
Keyword(s):  
Crystal Structures ◽  
Powder Diffraction ◽  
Room Temperature ◽  
Rietveld Refinements ◽  
Space Group ◽  
X Ray ◽  
Precise Characterization

The crystal structures of the chiolite-related room temperature phases α-Na5M3F14 (MIII=Cr,Fe,Ga) are determined. For all of them, the space group is P21/n, Z=2; a=10.5096(3) Å, b=7.2253(2) Å, c=7.2713(2) Å, β=90.6753(7)° (M=Cr); a=10.4342(7) Å, b=7.3418(6) Å, c=7.4023(6) Å, β=90.799(5)° (M=Fe), and a=10.4052(1) Å, b=7.2251(1) Å, c=7.2689(1), β=90.6640(4)° (M=Ga). Rietveld refinements produce final RF factors 0.036, 0.033, and 0.035, and RWP factors, 0.125, 0.116, and 0.096, for MIII=Cr, Fe, and Ga, respectively. The MF6 polyhedra in the defective isolated perovskite-like layers deviate very few from perfect octahedra. Subtle octahedra tiltings lead to the symmetry decrease from the P4/mnc space group adopted by the Na5Al3F14 chiolite aristotype to the P21/n space group adopted by the title series. Facile twinning precluded till now the precise characterization of these compounds.

Structural evolution of NASICON-type Li1+xAlxGe2−x(PO4)3 using in situ synchrotron X-ray powder diffraction

2016 ◽  
Vol 4 (20) ◽  
pp. 7718-7726 ◽  
Author(s):  
Dorsasadat Safanama ◽  
Neeraj Sharma ◽  
Rayavarapu Prasada Rao ◽  
Helen E. A. Brand ◽  
Stefan Adams
Keyword(s):  
Solid Electrolyte ◽  
Diffraction Study ◽  
Powder Diffraction ◽  
Structural Evolution ◽  
X Ray Diffraction ◽  
X Ray ◽  
Nasicon Type ◽  
Precursor Glass

In situ synchrotron X-ray diffraction study of the synthesis of solid-electrolyte Li1+xAlxGe2−x(PO4)3 (LAGP) from the precursor glass reveals that an initially crystallized dopant poor phase transforms into the Al-doped LAGP at 800 °C.

Komplexe des 1-Thia-4,7-diazacyclononans (L) mit Blei(II), Indium(III), Thallium(I) und (III) Kristallstruktur von [LPb][PbBr4] / Complexes of 1-Thia-4,7-diazacyclononane (L) with Lead(II), Indium(III), Thallium(I) and (III) Crystal Structure of [LPb][PbBr4]

1988 ◽  
Vol 43 (5) ◽  
pp. 567-570 ◽  
Author(s):  
Peter Hoffmann ◽  
Franz-Josef Hermes ◽  
Rainer Mattes
Keyword(s):  
Crystal Structure ◽  
Lone Pair ◽  
Tridentate Ligand ◽  
Crystal Data ◽  
Orthorhombic Space Group ◽  
Space Group

Abstract The reaction of 1-thia-4,7-diazacyclononane (C6H14N2S = L) with salts containing Tl(I) and (III), In(III) and Pb(II) ions yields 1:1 complexes, which can be crystallized as halide or Perchlorate salts. The structure of [LPb][PbBr4] (5) has been determined: Crystal data: orthorhombic, space group P212121, a = 853.2(6), b = 1000.1(4), c = 1860(1) pm, Z = 4. Pb2+ in the [LPb]2+ cation is seven-coordinated by the tridentate ligand and a square of four Br- ions. The Pb-S distance, 286.0(5) pm, is rather short, the lone pair stereochemically activ. The PbBr4- ions are polymeric with octahedrally coordinated lead(II) atoms.

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