(Y1−x)Ba2Cu3O6+δ (δ≤0.2): Consequences of Doping Tetragonal 123-Type to Induce Superconductivity

1989 ◽  
Vol 156 ◽  
Author(s):  
John B. Parise ◽  
Pratibha L. Gai ◽  
M. K. Crawford ◽  
Eugene M. McCarron
Keyword(s):  
Electron Microscopy ◽  
Structural Model ◽  
Complex Mixture ◽  
High Resolution Electron Microscopy ◽  
Nominal Composition ◽  
Superconducting Transition ◽  
Neutron Diffraction Data ◽  
Structural Refinement ◽  
Copper Oxidation ◽  
Resolution Electron

ABSTRACTSubstitution of Ca(II) for Y(III) into tetragonal YBa2Cu3O6 has been achieved and a superconducting transition has been observed for a material of nominal composition (Y0.5Ca0.5) Ba2Cu3O6 (Tc (onset) ˜50K) [1]. Observations using high resolution electron microscopy show samples with x < 0.3 consist of a complex mixture, including (Y, Ca) Ba2Cu3O6+δ, YBa2Cu3O6+δ, and BaCuO2. Further, structural refinement using neutron diffraction data provide evidence of a solid solution limit at x ˜ 0.3. A direct analogy can be drawn between superconducting (Y1−xCax)Ba2Cu3O6 (0.1 < x < 0.3) and superconductors of the type (Y1−xCax)Pb2Sr2Cu3O8 and (La2−xM(II)x)CuO4. Substitution of the Ca(II) for Y(III) effectively increases the formal copper oxidation state. The refined structural model is fully consistent with partially oxidized CuO2 sheets separated by linear O-Cu(I)-O units.

High-resolution transmission electron microscopy study of the φ′- and δ-AlON spinel phases of the pseudo-binary section AlN–Al2O3

1999 ◽  
Vol 32 (4) ◽  
pp. 755-760 ◽  
Author(s):  
P. Tabary ◽  
C. Servant ◽  
M. Guymont
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Structural Model ◽  
Spinel Phase ◽  
High Resolution Electron Microscopy ◽  
Microscopy Study ◽  
Electron Microscopy Study ◽  
Resolution Electron ◽  
Spinel Phases ◽  
Binary Section

A previously proposed structural model [Tabary & Servant (1999).J. Appl. Cryst.32, 253–272] for the φ′- and δ-AlON spinel phases, which allows for the double modulation of composition and displacement of cations and anions and which describes both phases and their relationships to the γ-AlON spinel phase, is here supported by high-resolution electron microscopy observations.

Post-annealing induced defects and their influences on Bi2Sr2CaCu2Oy superconducting thin films

1995 ◽  
Vol 10 (8) ◽  
pp. 1872-1877 ◽  
Author(s):  
Xiao Feng Zhang
Keyword(s):  
Electron Microscopy ◽  
Thin Films ◽  
Large Angle ◽  
High Resolution Electron Microscopy ◽  
Superconducting Thin Films ◽  
Superconducting Transition ◽  
Secondary Phases ◽  
Post Annealing ◽  
Resolution Electron ◽  
Induced Defects

Defects in Bi2Sr2Can-1CunOy superconducting thin films annealed in an oxygen atmosphere are examined by high-resolution electron microscopy (HREM). In addition to the majority 2212 (n = 2) phase, subsequent slabs of other homologous phases with n values up to n = 10 are found intergrown in the films. Large-angle tilt grain boundaries and various secondary phases such as CuO, Sr-Cu-O oxides are formed in the films. The occurrence of these defects is attributed to an inhomogeneous Sr, Ca, and Cu distribution induced by the post-annealing. Superconducting transition temperature (Tc) is increased by the annealing under suitable conditions.

Elucidation of the crystal structure of oxyapatite by high-resolution electron microscopy

1999 ◽  
Vol 55 (2) ◽  
pp. 170-176 ◽  
Author(s):  
Peter Alberius Henning ◽  
Angel R. Landa-Cánovas ◽  
Ann-Kristin Larsson ◽  
Sven Lidin
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Structural Model ◽  
High Resolution Electron Microscopy ◽  
Group Symmetry ◽  
Space Group ◽  
Threefold Symmetry ◽  
Transmission Electron ◽  
Crude Model ◽  
Resolution Electron

High-resolution electron-microscopy (HREM) images from different hydroxyapatite (OHAp) samples showed p3 projection symmetry along [001] instead of the p6 projection symmetry compatible with the space group P6_3/m of OHAp. Image processing was used to establish without ambiguity that threefold symmetry dominates the images along [001]. OHAp crystals decompose in the transmission electron microscope and it is concluded that the threefold symmetry observed corresponds to an early step in the decomposition process, the dehydration of OHAp to oxyapatite (OAp). A structural model for OAp where every second O atom along the 63 axis in OHAp is removed has the maximal space-group symmetry P\bar6. This is compatible with the p3 projection symmetry observed. Atomic shifts in this OAp model compared to the OHAp structure were estimated using the HREM images and geometric optimizations of the atomic structure. No refinements of the atomic coordinates against diffraction data were possible but the simulated HREM images of this crude model fit well with the experimental images.

Tl2Ba2CaCu2O8: STRUCTURE AND SUPERCONDUCTIVITY

1988 ◽  
Vol 02 (05) ◽  
pp. 681-687 ◽  
Author(s):  
A. MAIGNAN ◽  
C. MICHEL ◽  
M. HERVIEU ◽  
C. MARTIN ◽  
D. GROULT ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Calcium Ions ◽  
Structural Model ◽  
High Resolution Electron Microscopy ◽  
Extended Defects ◽  
Superconducting Properties ◽  
Local Composition ◽  
X Ray ◽  
Resolution Electron ◽  
Pure Phase

Tl 2 Ba 2 CaCu 2 O 8 has been synthesized as a pure phase by reaction in sealed quartz tube. The structural model of this oxide has been established from X-ray diffractograms and high resolution electron microscopy. This tetragonal structure (a=3.860 Å, c=29.388 Å, space group I4/mmm) can be described as formed of [ Ba 2Tl2Cu2 O 8]∞ layers interleaved with calcium ions. These layers are themselves described as the intergrowth of sodium chloride type [TIO] ∞ layers of corner-sharing pyramids [ BaCuO 3]∞ leading to the formulation [( BaCuO 3)2 (TIO) 2]∞. Such a perfect structure Tl2 Ba 2 CaCu 2O8, which contains only Cu(II) cannot be at the origin of the superconductivity at 110K. The superconducting properties may in fact be explained by the observation by HREM of extended defects of local composition “ TlBa 2 CaCu 2O7” for which a structural model is proposed. In a more general way the creation of thallium deficiency, according to the formulation Tl2−x Ba 2 CaCu 2 O 8 could be at the origin of superconductivity.

Investigation of structural model of amorphous boron by high resolution electron microscopy

1991 ◽  
Author(s):  
A. L. Vasiljev ◽  
M. A. Gribeluk ◽  
E. V. Orlova ◽  
A. M. Dovidenko ◽  
G. P. Tsiskarishvili ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Structural Model ◽  
High Resolution Electron Microscopy ◽  
Amorphous Boron ◽  
Resolution Electron

HREM STUDIES OF THE SUPERCONDUCTING PHASE Tl2Ba2Ca2Cu3Ox

1989 ◽  
Vol 03 (04) ◽  
pp. 361-367
Author(s):  
J.G. ZHENG ◽  
J. CHEN ◽  
J.G. JIANG ◽  
Y.H. LIANG ◽  
S.Y. DING ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Grain Boundaries ◽  
Large Angle ◽  
Amorphous State ◽  
High Resolution Electron Microscopy ◽  
Superconducting Phase ◽  
Nominal Composition ◽  
Resolution Electron ◽  
Superconducting Ceramics

The superconducting phase Tl 2 Ba 2 Ca 2 Cu 3 O x (Tl2223) has been identified in high-T c superconducting ceramics with nominal composition of Tl 2 Ba 2 Ca 2 Cu 3. The configurations of grains and grain boundaries have also been observed directly by high resolution electron microscopy [HREM]. The small angle grain boundaries are mixed with both translation and orientation characteristics. The boundary regions are nearly parallel to (100) to (010) in crystal state, While in amorphous state, they are nearly parallel to (001). There also exists large angle grain boundaries in TlBaCaCuO superconductor.

Initial stages of electron beam-induced transformations in potassium β‴-Ferrite, KFe17O25

1990 ◽  
Vol 48 (4) ◽  
pp. 810-811
Author(s):  
J.L. Hutchison ◽  
Y. Matsui ◽  
F.J. Lincoln
Keyword(s):  
Electron Microscopy ◽  
Structural Changes ◽  
High Resolution Electron Microscopy ◽  
Hexagonal Structure ◽  
Atomic Level ◽  
Nominal Composition ◽  
List Type ◽  
Type Number ◽  
Resolution Electron ◽  
Topotactic Transformation

Potassium β’’’-ferrite, nominal composition KFe17O25 and isostructural with sodium β’’’- alumina, has a hexagonal structure consisting of spinel blocks (SB) separated by loosely packed conduction planes (CP) containing relatively mobile K+ cations. Various structural changes which occur during electron irradiation have been characterised by high resolution electron microscopy and may be summarised as follows:1Migration of K+ and O2−from the conduction planes, followed by2Frequent collapse of CP.3Topotactic transformation of the resulting multiply-twinned spinel layers to form broad laths of magnetite, Fe304.4Gradual growth of wüstite, Fe1-xO on exposed surfaces.We have examined KFe17O25 at 400 kV, using a JEOL 4000EX, the resolution (1.65 Å)being sufficient to resolve all cation rows along two main crystallographic directions, and We could thus monitor the earliest stages of structural transformation at the atomic level.

High-Resolution Electron Microscopy of Planar Defects in Ain.

1990 ◽  
Vol 183 ◽  
Author(s):  
Stuart Mckernan ◽  
M. Grant Norton ◽  
C. Barry Carter
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Structural Model ◽  
Antiphase Boundary ◽  
High Resolution Electron Microscopy ◽  
Second Phase ◽  
Polycrystalline Aluminum ◽  
Basal Segment ◽  
Planar Fault ◽  
Resolution Electron

AbstractThe defects which occur in polycrystalline aluminum nitride are very detrimental to the beneficial physical and electrical properties. 'Dome-like' or 'D' defects, consisting of a flat basal fault joined to a curved planar fault, are examined by high-resolution electron microscopy. The basal segments are shown to contain a thin ∼5Å layer of a second phase and are associated with a stacking-fault and an antiphase boundary. A structural model is proposed for the defect which incorporates a layer of alumina at the basal segment of the 'D' defect. The formation of thisdefect is discussed.

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