Es. Reddy et T. Rajasekharan, NUCLEATION AND GROWTH OF THE ORTHORHOMBIC PHASE IN MELT-TEXTURED YBA2CU3O6+DELTA, Physica. C, Superconductivity, 279(1-2), 1997, pp. 56-62
The nucleation and growth of the orthorhombic phase by transformation
through oxygen ordering from the tetragonal phase in melt textured YBa
2Cu3O6+delta (123) are investigated by polarized light microscopy. The
samples for observation were collected from the interior of partially
oxygenated bulk melt textured material. The orthorhombic phase is obs
erved to nucleate basically at three different sites, viz. along domai
n boundaries, at platelet boundaries and around macroscopic cracks. Th
e nuclei at domain boundaries are observed to grow along the platelet
boundary gaps with a cellular morphology with sharp tips, whereas the
growth front of the phase growing from the boundaries of platelets int
o their interior is planar. The growth of the phase from the domain bo
undaries into the domains differs depending on the orientation of the
platelets at the point of nucleation. The origin of inter-platelet gap
s in the melt processed material is discussed in the light of the obse
rvations made during this work. The ratio of growth rates of the ortho
rhombic phase along the gaps and into the platelets is estimated. (C)
1997 Elsevier Science B.V.