Ordered Structures in Gd2CuO4 and isostructural cuprates

1989 ◽  
Vol 47 ◽  
pp. 160-161
Author(s):  
T. E. Mitchell ◽  
T. Roy ◽  
Z. Fisk ◽  
S-W Cheong ◽  
J. D. Thompson ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Single Crystals ◽  
Liquid Nitrogen ◽  
High Resolution Electron Microscopy ◽  
Ion Milling ◽  
Ordered Structures ◽  
Resolution Electron

INTRODUCTION.The lanthanide cuprates Ln2CuO4 (Ln = Pr, Nd, Eu, Gd, etc.), have a a triple perovskite unit cell.The structure is tetragonal, 14/mmm, a ∼ 0.39nm, c ∼1.19nm, with layered nets of [CuO4] squares. By contrast, the structure of La2CuO4, which also has a triple perovskite cell, contains layers of [CuO6] octahedra. La2CuO4 becomes superconducting by doping with SrO while Ln2CuO4 becomes superconducting by doping with CeO2 for Ln = Pr, Nd and Sm. Both La2CuO4 and YBa2Cu3O7 have a tetragonal-to-orthorhombic transformation while Ln2CuO4 remains tetragonal.The present study was undertaken to investigate microstructures in the lanthanide cuprates.EXPERIMENTAL. The Ln2CuO4 single crystals were grown as plates from a PbO or CuO flux. Specimens for TEM were prepared by ion milling using a liquid nitrogen specimen cooler. High resolution electron microscopy (HREM) was performed on either a Philips CM3OST at 300kV or a JEM4000FX at 400kV.

Hrem Visualization of Light Atoms: An Application to the Study of Carbon Defects in Ordered Transition Metal Carbides

1990 ◽  
Vol 183 ◽  
Author(s):  
T. Epicier
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Transition Metal ◽  
High Resolution Electron Microscopy ◽  
Metal Carbides ◽  
Ordered Structures ◽  
Transition Metal Carbides ◽  
Resolution Electron ◽  
Light Atoms ◽  
Complex Crystal

AbstractThis paper gives an overview of recent High Resolution Electron Microscopy (HREM) observations of transition metal carbides. The main point is to show how HREM can be used to study a sublattice of light atoms within a complex crystal. General tendencies of this approach will be outlined, which appear, to a large extent, to be common to similar possible studies of other compounds such as nitrides, borides or oxides. Specifically, attention is focused on studies of long-range ordered structures in carbides, due to non-stoichiometry accommodated by metalloid vacancies. Various examples are given for representative compounds, including V8C7, V6C, 5, Nb6C5 and W2C.

L12- and L10-like cation-ordered structures in ZrO2–Y2O3 ceramics

2001 ◽  
Vol 16 (6) ◽  
pp. 1806-1813 ◽  
Author(s):  
J. C. Rao ◽  
Y. Zhou ◽  
D. X. Li
Keyword(s):  
Electron Microscopy ◽  
Computer Simulation ◽  
High Resolution ◽  
Annealing Temperature ◽  
High Resolution Electron Microscopy ◽  
Energy Dispersive ◽  
Ordered Structures ◽  
X Ray ◽  
Resolution Electron

Y0.25Zr0.75O2−x and Y0.5Zr0.5O2−y phases, with L12- and L10- like cation-ordered structures, respectively, have been found in ZrO2–Y2O3 ceramics in both the sintered and annealed states. High-resolution electron microscopy, energy-dispersive x-ray spectroscopy and computer simulation have been used to reveal the presence of the phases. The formation of Y0.25Zr0.75O2−x and Y0.5Zr0.5O2−y phases was initiated during the sintering procedure and developed with the increase in annealing temperature and time. Segregation of yttrium, which was prevalent in different regions even within one grain, induced the formation of Y0.25Zr0.75O2−x and Y0.5Zr0.5O2−y phases.

Structural imaging of polytypoids in high Tc oxide superconductors

1989 ◽  
Vol 47 ◽  
pp. 156-157
Author(s):  
R. Ramesh ◽  
E. Wang ◽  
J.M. Tarascon ◽  
G. Thomas
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Liquid Nitrogen Temperature ◽  
High Resolution Electron Microscopy ◽  
Oxide Superconductors ◽  
Ion Milling ◽  
Resolution Electron ◽  
The Matrix ◽  
Diffraction Patterns ◽  
Processing Techniques

The structure of the superconducting polytypoid in the newly discovered high Tc super conducting system, Pb2Sr2Cu2Oy has been examined by high resolution electron microscopy, electron diffraction and xray microanalysis. High resolution imaging has shown the presence of the Pb2Sr2Cu2Oy at the grain boundaries. In analogy to the Bi-Ca-Sr-Cu-O(BCSCO)system, it is suggested that this polytypoid could have a lower transition temperature compared to the matrix. This may explain the steps in the resistivity plot. It is also shown that complex cationic ordering, such as replacement of Sr by Ca and/or Y, could lead to extra reflections in the diffraction patterns.Pb-Sr-(Ca-RE)-Cu-O sintered samples were prepared by standard solid state processing techniques. Samples were prepared under 1% flowing oxygen. Samples for electron microscopy were prepared by argon ion milling at liquid nitrogen temperature at 6kV. High resolution electron microscopy was carried out in the Berkeley Atomic Resolution Microscope at 800kV.

Sign in / Sign up

Export Citation Format

Share Document