ISOMORPHIC SUBSTITUTIONS IN CATION SUBLATTICES OF ORTHORHOMBIC Y-123 CUPRATES AND MICROTWINNING .2. Y0.81CA0.11BA2.0CU2.92ZN0.04O6.41 (ORTHORHOMBIC-II PHASE)
Av. Arakcheeva et al., ISOMORPHIC SUBSTITUTIONS IN CATION SUBLATTICES OF ORTHORHOMBIC Y-123 CUPRATES AND MICROTWINNING .2. Y0.81CA0.11BA2.0CU2.92ZN0.04O6.41 (ORTHORHOMBIC-II PHASE), Crystallography reports, 42(4), 1997, pp. 582-587
Crystals of Y-123-cuprate of the composition Y0.81Ca0.11Ba2.0Cu2.92Zn0
.04O6.41 have been studied by the single-crystal X-ray method (the str
ucture type of orthorhombic phase II is R-II = YBa2Cu3O6.5 with a doub
le parameter a in comparison with that of the orthorhombic phase I): a
= 2 x 3.828(1), b = 3.883(1), and c = 11.689(4) Angstrom, Z = 2; sp.
gr. Pmmm, R-aniso = 0.045 for the 681 independent reflection. The defi
cit in O atoms is associated with vacancies in the position of the api
cal oxygen atom. Along with the previously observed displacements of B
a atoms in the [100] direction, the analogous displacements of (Y, Ca)
atoms are found. The methods of high-resolution electron microscopy p
rovided observation of microtwinning interpreted as twinning by the ax
is 2 in contrast to the well known twinning in the m-plane. The depend
ence of two types of microtwinning on the oxygen content is also discu
ssed.