2.4 HTS bulk materials Ë 33Fig. 2.3:Three shapes of HTS YBCO bulks in the top view, (a) regular hexagon, (b) square and
(c) cylinder (Beijing General Research Institute for Nonferrous Metals, China).
ability to trap magnetic flux. However, it is difficult to obtain a single-grain bulk larger
than about 80 mm because of undesirable nucleation at the positions away from the
seed crystal [99].
In order to develop manned Maglev trains, high-quality MTG YBCO bulks [100]
(Fig. 2.3a–c) were prepared by the Beijing General Research Institute for Nonferrous
Metals in 2000. The superconductors used in the first manned HTS Maglev test vehicle
in the world were the YBCO bulk 30-mm-diameter samples (Fig. 2.3c). Single- and
multi-seeded melt-textured HTS YBCO bulks [101, 102] have been developed by the
Adelwitz Technologiezentrum GmbH (ATZ), Germany. Some basic material parameters
of ATZ melt-textured YBCO are summarized in Tab. 2.4. The three-seed YBCO bulks
have a size of 67× 35 ×15 mm (Fig. 2.4) and were used in the Maglev vehicle at the
University of Rio de Janeiro in 2011 and the Applied Superconductivity Laboratory
(ASCLab), Southwest Jiaotong University, China, in 2013.
A microgravity experiment for growing large GdBCO bulks, 127 mm in diameter
and 20 mm in thickness, was successfully performed on the spacecraft in 2003 [103].
Colleagues in the field of superconductor research are looking forward for more data
from this large GdBCO bulk.
Tab. 2.4:YBCO bulk material parameters [101].
Parameters Value
Transition temperatureTc 92 K (− 181 °C)
Specific resistance휌 300 0.6–0.8 mΩ⋅cm
Density (theoretical) 6.38 g/cm^3
Density (experimental) 5.95 g/cm^2 (93%)
Specific heat capacityc 300 0.18 W⋅s⋅g−^1 ⋅K−^1
Calorimeter meas.cRT 0.25 W⋅s⋅K−^1 ⋅g−^1
Coeflcient heat transfer휆 4 W⋅m−^1 ⋅K−^1 ‖c
9 W⋅m−^1 ⋅K−^1 ‖a,b
6–7 W⋅m−^1 ⋅K−^1 poly
Lin. expansion coeflcient 5 − 8 × 10 −^6 K−^1
Tensile strength 25–30 MPa
Critical current densityJc 104 –10^5 A⋅cm−^2 (77 K, 0 T)