The Influence of Personality on a Group-Level Process: Shy Hermit Crabs Make Longer Vacancy Chains

It has long been known that defects such as stacking faults and voids can be quenched from various alloyed metals heated to near their melting point. Today it is common practice to irradiate samples with various ionic species of rare gases which also form voids containing solidified phases of the same atomic species, e.g. ref. 3. Equivalently, electron irradiation has been used to produce damage events, e.g. ref. 4. Generally all of the above mentioned studies have relied on diffraction contrast to observe the defects produced down to a dimension of perhaps 10 to 20Å. Also all these studies have used ions or electrons which exceeded the damage threshold for knockon events. In the case of higher resolution studies the present author has identified vacancy and interstitial type chain defects in ion irradiated Si and was able to identify both di-interstitial and di-vacancy chains running through the foil.

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A study of oxygen and vacancy ordering in YBa2Cu3O7−x

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100152793 ◽

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.

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