Electronic Resource
[S.l.]
:
American Institute of Physics (AIP)
Journal of Applied Physics
76 (1994), S. 163-171
ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
The structural transformations occurring during high-energy mechanical milling and subsequent annealing of YBa2Cu3O7−δ samples have been studied. A high initial oxygen content favors the formation of a metastable (Y0.33Ba0.66)CuO3−x disordered cubic phase. The cubic phase decomposes into a nanocrystalline mixture of Y2BaCuO5 and an yttrium deficient amorphous phase upon further milling. The crystallization enthalpy of the amorphous phase was estimated to be approximately 72.2 kJ/mol with a corresponding activation energy of 800±80 kJ/mol. Upon heating the nanocrystalline cubic phase transforms to the high-oxygen tetra X (O6.77) nonsuperconducting phase. Under oxygen, this last phase is stable up to 930 °C where it transforms to the tetra II low-oxygen (O〈6.4) structure which reverts to the ortho I superconducting phase after adequate cooling. A structural model is proposed in which the formation of coherent domain boundaries and the unusually short c axis associated with the tetra X phase are related to the reordering of the Y-Ba sublattice of the metastable cubic phase. The relative stability of the cubic and tetra X phases as a function of the initial oxygen content before milling indicates that the oxygen concentration may be higher at the domain boundaries.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.357123
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