A study of oxygen and vacancy ordering in YBa2Cu3O7−x

1989 ◽  
Vol 47 ◽  
pp. 164-165
Author(s):  
Y. P. Lin ◽  
A. H. O’Reilly ◽  
J. E. Greedan ◽  
M. Post
Keyword(s):  
Electron Microscopy ◽  
Neutron Diffraction ◽  
Oxygen Content ◽  
Carbon Film ◽  
Nitrogen Atmosphere ◽  
Vacancy Ordering ◽  
Powder Samples ◽  
Vacancy Chains ◽  
Chain Ordering

In the basal planes of the orthorhombic YBa2Cu3O7-X compound with x=0.07, which has a Tc of around 90K, chains of copper-oxygen are formed along the [010] direction. Previous investigations on the variation of Tc with oxygen content have shown the existence of a plateau at Tc = 60K for x=0.3 to 0.4, suggesting the presence of a separate phase. This phase has also been identified to be orthorhombic, but with a 2x superlattice along [100] of the parent structure, and the superlattice has been attributed to the formation of alternating copper-oxygen and copper-vacancy chains. In our work, we have studied the chain ordering phenomenon by electron microscopy and neutron diffraction on samples with different oxygen contents. We report here some of our electron microscopy findings for samples with x=0.4.Powder samples of YBa2Cu3O7-X were prepared by controlled re-oxidation of previously reduced material. For electron microscopy, the sample was dry ground using a mortar and pestle in a dry nitrogen atmosphere without the use of any solvent and transferred dry onto holey carbon film for examination in a Philips CM12 microscope.

Transmission Electron Microscopy studies of the vacancy ordering in YSI2-X thin films

1991 ◽  
Vol 49 ◽  
pp. 562-563
Author(s):  
F.-R. Chen ◽  
T. L. Lee ◽  
L. J. Chen
Keyword(s):  
Crystal Structure ◽  
Electron Microscopy ◽  
Thin Films ◽  
Diffraction Pattern ◽  
Annealing Temperature ◽  
Lattice Mismatch ◽  
Si Substrate ◽  
Metal Thin Films ◽  
Transmission Electron ◽  
Vacancy Ordering

YSi2-x thin films were grown by depositing the yttrium metal thin films on (111)Si substrate followed by a rapid thermal annealing (RTA) at 450 to 1100°C. The x value of the YSi2-x films ranges from 0 to 0.3. The (0001) plane of the YSi2-x films have an ideal zero lattice mismatch relative to (111)Si surface lattice. The YSi2 has the hexagonal AlB2 crystal structure. The orientation relationship with Si was determined from the diffraction pattern shown in figure 1(a) to be and . The diffraction pattern in figure 1(a) was taken from a specimen annealed at 500°C for 15 second. As the annealing temperature was increased to 600°C, superlattice diffraction spots appear at position as seen in figure 1(b) which may be due to vacancy ordering in the YSi2-x films. The ordered vacancies in YSi2-x form a mesh in Si plane suggested by a LEED experiment.

Transmission electron microscopy observation in a liquid-phase-sintered SiC with oxynitride glass

2001 ◽  
Vol 16 (8) ◽  
pp. 2189-2191 ◽  
Author(s):  
Guo-Dong Zhan ◽  
Mamoru Mitomo ◽  
Young-Wook Kim ◽  
Rong-Jun Xie ◽  
Amiya K Mukherjee
Keyword(s):  
Electron Microscopy ◽  
Liquid Phase ◽  
High Resolution Electron Microscopy ◽  
Nitrogen Atmosphere ◽  
X Ray Diffraction ◽  
Sintering Additive ◽  
Transmission Electron ◽  
High Annealing ◽  
Resolution Electron ◽  
Oxynitride Glass

Using a pure α–SiC starting powder and an oxynitride glass composition from the Y–Mg–Si–Al–O–N system as a sintering additive, a powder mixture was hot-pressed at 1850 °C for 1 h under a pressure of 20 MPa and further annealed at 2000 °C for 4 h in a nitrogen atmosphere of 0.1 MPa. High-resolution electron microscopy and x-ray diffraction studies confirmed that a small amount of β–SiC was observed in the liquid-phase-sintered α–SiC with this oxynitride glass, indicating stability of β–SiC even at high annealing temperature, due to the nitrogen-containing liquid phase.

Influence of ethanol on the chain-ordering of carbonised polyaniline

2013 ◽  
Vol 67 (8) ◽  
Author(s):  
Zuzana Morávková ◽  
Miroslava Trchová ◽  
Elena Tomšík ◽  
Jaroslav Stejskal
Keyword(s):  
Molecular Structure ◽  
Pure Water ◽  
Nitrogen Atmosphere ◽  
Ethanol Mixture ◽  
Electron Microscopies ◽  
X Ray Scattering ◽  
Transmission Electron ◽  
Pani Salt ◽  
Chain Ordering ◽  
Pani Base

AbstractPolyaniline (PANI) was prepared by the oxidation of aniline hydrochloride with ammonium peroxydisulphate in water or in a water-ethanol mixture. In the presence of ethanol, PANI nanotubes and nanorods were observed. Both products were carbonised in a nitrogen atmosphere at 650°C. Initial and carbonised products were characterised by scanning and transmission electron microscopies, thermogravimetric analysis and wide-angle X-ray scattering. Their molecular structure was studied by UV-VIS, infrared, and Raman spectroscopies. Carbonised sample obtained from the PANI salt prepared in the presence of ethanol exhibits Raman spectrum which corresponds to a more ordered carbon-like material than carbonised samples obtained from the PANI base and the PANI salt prepared in pure water. The influence of ethanol present in the reaction mixture on the molecular and supra-molecular structure of PANI and, consequently, on the enhancement of chainordering of carbonised PANI is discussed.

In situ Neutron Diffraction on DxNb2O5

1998 ◽  
Vol 53 (5-6) ◽  
pp. 557-561
Author(s):  
Tobias Unruh ◽  
Günter Schwitzgebel ◽  
Clemens Ritter
Keyword(s):  
Neutron Diffraction ◽  
Structural Changes ◽  
Electrochemical Cell ◽  
Host Lattice ◽  
Deuterium Content ◽  
Inhomogeneous Distribution ◽  
Powder Samples ◽  
Diffraction Patterns ◽  
In Situ Neutron Diffraction

Abstract DxNb2O5 is thermodynamically unstable. Therefore, neutron diffraction measurements were performed in the electrochemical cell used for the intercalation of deuterium into sintered Nb2O5 powder samples. Diffraction patterns were recorded at equilibrium potentials of -443, -428, -332 and -197 mV vs. NHE (corresponding to x = 0.232, x = 0.23, x = 0.21 and x = 0.06). The structural changes in Nb2O5 caused by the deuterium insertion are small but could be determined reproducibly. The lattice parameters of the host lattice exhibit a characteristic dependence on the deuterium content of the bronze. A model has been developed for the partially inhomogeneous distribution of the deuterium in the Nb2O5 unit cell, which explains the changes of the peak intensities observed in the low angle region (6° ≤ 2θ ≤ 18°).

Strukturen cäsiumhaltiger Fluoride, II1 Die Kristall- und Magnetische Struktur von CsFeF4 / Crystal and Magnetic Structure of CsFeF4

1974 ◽  
Vol 29 (3-4) ◽  
pp. 139-148 ◽  
Author(s):  
D. Babel ◽  
F. Wall ◽  
G. Heger
Keyword(s):  
Neutron Diffraction ◽  
Single Crystals ◽  
Magnetic Structure ◽  
Structure Determination ◽  
Mean Value ◽  
X Ray ◽  
Magnetic Structures ◽  
Powder Samples ◽  
Crystal And Magnetic Structure ◽  
Improved Model

The results of an X-ray structure determination on single crystals of CsFeF4 are reported. The compound crystallizes tetragonally with α = 7.794, c = 6.553 Å, z = 4, in spacegroup P4/nmm-D4h7 and is a hitherto unknown superstructure variant of the TlAlF4-type. Cesium exhibits 12-coordination (mean value Cs-F = 3.25 Å); the FeF6-octahedra are characteristically shortened normal to the FeF4⁻-layers (Fe-F = 1.962/1.861Å). An improved model is proposed and verified for a related structure of RbFeF4, showing the same features. Neutron diffraction studies on powder samples of CsFeF4 show that both compounds are identical as for their magnetic structures.

Neutron diffraction by time-of-flight spectroscopy on powder samples up to 15 GPa

1992 ◽  
Vol 9 (1-6) ◽  
pp. 179-193 ◽  
Author(s):  
J. M. Besson ◽  
R. J. Nelmes ◽  
J. S. Loveday ◽  
G. Hamel ◽  
Ph. Pruzan ◽  
...  
Keyword(s):  
Neutron Diffraction ◽  
Time Of Flight ◽  
Powder Samples ◽  
Time Of Flight Spectroscopy
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