ISSN:
1572-9605
Keywords:
Superconductivity
;
Cu-O chain
;
dynamics
;
Mössbauer
;
57Co sites
Source:
Springer Online Journal Archives 1860-2000
Topics:
Electrical Engineering, Measurement and Control Technology
,
Physics
Notes:
Abstract The dynamics of the Cu-O chain in YBa2Cu3O7−δ was investigated by emission Mössbauer spectroscopy, using57Co dopant to microprobe the Cu(1) site. The transformation of the 5-coordinate trigonal-bipyramidal cobalt configuration (species B) to a square-pyramidal one (species C) is induced by the zig-zag motion of the chain. The thermodynamical parameters associated with this conversion were determined, ΔH 0=38±5 kJ/mol (0.4 eV) and ΔS 0=127±20 J/K. About 40% of species C does not convert into B at all. We suggest that the inconvertible C has a static square-pyramidal configuration at twin-boundaries where the chain motion is damped. In the57Fe-doped compound, the iron atoms form linear clusters, and the Cu-O chain motion and also the B-to-C conversion is retarded in the temperature range 200–350 K. A new minor Co species similar to B (namely, B') is reported, which is presumably situated on the grain boundaries. Its nonmetallic environment is reflected in the relatively large value of isomer shift. The properties of the electric field gradient tensor at major Co(Fe) sites are also discussed.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00617472
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