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 (Sm-123), neodymium (Nd-123 and Nd-422), gadolinium (Gd-123) and europium (Eu-123) 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.