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Proceedings Paper

Phase control in La-214 epitaxial thin films
Author(s): Michio Naito; Akio Tsukada; Tine Greibe; Hisashi Sato
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Paper Abstract

The lanthanide (Ln) copper oxides of the general chemical formula Ln2CuO4 take two different crystal structures: K2NiF4(T) and Nd2CuO (T'). La2CuO4 takes the T structure by high-temperature bulk processes. The "thermal expansion mismatch" between the La-O and Cu-O bonds predicts that the T' phase of La2CuO4 can be stabilized at synthesis temperatures below 425oC. Such low synthesis temperatures are difficult to access by bulk processes, but easy by thin-film processes. We have surveyed growth parameters in molecular beam epitaxy, and succeeded in the selective stabilization of T- and T'-La2CuO4. From our observations, it turns out that the growth temperature as well as the substrate play a crucial role in the selective stabilization: the T' structure is stabilized at low growth temperatures (< 600oC) and with substates of as < 3.70 angstrom or as > 3.90 angstrom, while the T structure is stabilized at high growth temperatures (>650oC) or with substrates of as ~ 3.70 - 3.85 angstrom. We have also been attempting hole (Ca, Sr, and Ba) and electron (Ce) doping into both of T- and T'-La2CuO4. In T-La2CuO4, hole doping produces the well-known LSCO and LBCO. Surprisingly, contrary to the empirical law, electron doping is also possible up to x~ 0.06 - 0.08, although the films do not show superconductivity. In T'-La2CuO4, electron doping produces superconducting T'-(La,Ce)2CuO4 with Tc~ 30 K, although hole doping has as yet been unsuccessful.

Paper Details

Date Published: 7 November 2002
PDF: 15 pages
Proc. SPIE 4811, Superconducting and Related Oxides: Physics and Nanoengineering V, (7 November 2002); doi: 10.1117/12.455498
Show Author Affiliations
Michio Naito, NTT Corp. (Japan)
Akio Tsukada, Science Univ. of Tokyo (Japan)
Tine Greibe, NTT Corp. (Japan)
Hisashi Sato, NTT Corp. (Japan)

Published in SPIE Proceedings Vol. 4811:
Superconducting and Related Oxides: Physics and Nanoengineering V
Ivan Bozovic; Davor Pavuna, Editor(s)

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