TY - GEN
T1 - Phase control in La-214 epitaxial thin films
AU - Naito, Michio
AU - Tsukada, Akio
AU - Greibe, Tine
AU - Sato, Hisashi
AU - Tsukada, Akio
PY - 2002
Y1 - 2002
N2 - The lanthanide (Ln) copper oxides of the general chemical formula Ln(2)CuO(4) take two different crystal structures: K2NiF4 (T) and Nd2CuO4 (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 425degreesC. 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 (< 600degreesC) and with substrates of a(s) < 3.70 Angstrom or a(s) > 3.90 Angstrom, while the T structure is stabilized at high growth temperatures (> 650degreesC) or with substrates of a(s) similar to 3.70 - 3.95 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 similar to 0.06 - 0.08, although the films do not show superconductivity. In T'-La2CuO4, electron doping produces superconducting T'-(La,Ce)(2)CuO4 with T-c similar to 30 K, although hole doping has as yet been unsuccessful.
AB - The lanthanide (Ln) copper oxides of the general chemical formula Ln(2)CuO(4) take two different crystal structures: K2NiF4 (T) and Nd2CuO4 (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 425degreesC. 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 (< 600degreesC) and with substrates of a(s) < 3.70 Angstrom or a(s) > 3.90 Angstrom, while the T structure is stabilized at high growth temperatures (> 650degreesC) or with substrates of a(s) similar to 3.70 - 3.95 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 similar to 0.06 - 0.08, although the films do not show superconductivity. In T'-La2CuO4, electron doping produces superconducting T'-(La,Ce)(2)CuO4 with T-c similar to 30 K, although hole doping has as yet been unsuccessful.
KW - Phase control
KW - K2NiF4 structure
KW - Nd2CuO4 structure
KW - Molecular beam epitaxy
KW - Quasi-stable phase
U2 - 10.1117/12.455498
DO - 10.1117/12.455498
M3 - Article in proceedings
SN - 0-8194-4579-7
VL - 5
T3 - Proceedings of SPIE - The International Society for Optical Engineering
SP - 140
EP - 154
BT - Superconducting and Related Oxides
T2 - Conference on Superconducting and Related Oxides - Physics and Nanoengineering
Y2 - 8 July 2002 through 11 July 2002
ER -