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PhysicaC 152 (1988) 161-170 North-Holland, Amsterdam
 

Summary: PhysicaC 152 (1988) 161-170
North-Holland, Amsterdam
STRUCTURE AND FORMATION OF TWINS IN THE ORTHORHOMBIC YBa2CuJ0,_x
Mehmet SARIKAYA, Ryoichi KIKUCHI and Ilhan A. AKSAY
Department ofMaterials Science and Engineering, and Advanced Materials Technology Program, Washington Technology
Center, University of Washington, Seattle, WA 98195, USA
Received 19 January 1988
Structure and formation of twins in the orthorhomhic phase of YBaQ@_, samples, exhibiting bulk superconductivity at 90
K, are studied by transmission electron microscopy and modeling. Twinned domains with {110) twin boundaries form with
separation I which is dictated by energetic and geometrical requirements. Both of these requirements are related to Aa= b-a,
where b and a are lattice parameters of the orthorhombic phase. Geometrical requirement leads to the estimate that the stable
values of I are integer multiples of d= ab/ ($Aa). In some samples I's are regular, in others not. Deviation ofl from theoretically
expected stable separations is interpreted as due to local variation of oxygen ordering and/or local elastic strain. The twin bound-
ary has a structure different from the bulk orthorhombic phase and electron micrographs suggest that it has a width of 30-50 A.
In bulk samples twinned domains can be present at different stages of the growth process. These substructural variations suggest
that samples are at metastable equilibrium and are consistent with samples being in the superconducting glassy state.
1. Introduction
Recently, there is a growing interest in the possible
effects of substructural variations, i.e., various lat-
tice defects and inhomogeneities at nanometer range,

  

Source: Aksay, Ilhan A. - Department of Chemical Engineering, Princeton University

 

Collections: Materials Science