Compounds that have superconducting properties even in high magnetic fields and temperatures up to 77 kelvin. They are a high-temperature superconductor and a promising material for the production of magnetic coils for accelerators, tokamaks and stellarators. Any rare-earth element can be used in ReBCO. Yttrium (YBCO) is the best known, while lanthanum (LBCO), samarium (Sm123), neodymium (Nd123 and Nd422), gadolinium (Gd123) and europium (Eu123) are also used. The numbers among parenthesis indicate the molar ratio among rare-earth, barium and copper. The starting materials are brittle, but since 2010, it has been possible to manufacture ReBCO superconductors in bendable tapes.