Phase control in La-214 epitaxial thin films

Michio Naito; Akio Tsukada; Tine Greibe; Hisashi Sato

doi:10.1117/12.455498

7 November 2002 Phase control in La-214 epitaxial thin films

Michio Naito, Akio Tsukada, Tine Greibe, Hisashi Sato

Proceedings Volume 4811, Superconducting and Related Oxides: Physics and Nanoengineering V; (2002) https://doi.org/10.1117/12.455498
Event: International Symposium on Optical Science and Technology, 2002, Seattle, WA, United States

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 425^oC. 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 (< 600^oC) and with substates of a_s < 3.70 angstrom or a_s > 3.90 angstrom, while the T structure is stabilized at high growth temperatures (>650^oC) or with substrates of a_s ~ 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 T_c~ 30 K, although hole doping has as yet been unsuccessful.

Citation Download Citation

Michio Naito, Akio Tsukada, Tine Greibe, and Hisashi Sato "Phase control in La-214 epitaxial thin films", Proc. SPIE 4811, Superconducting and Related Oxides: Physics and Nanoengineering V, (7 November 2002); https://doi.org/10.1117/12.455498

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