High pressure synthesis of late rare earth RFeAs(O,F) superconductors; R = Tb and Dy.

New TbFeAs(O,F) and DyFeAs(O,F) superconductors with critical temperatures T(c) = 46 and 45 K and very high critical fields, >or=100 T, have been prepared at 1100-1150 degrees C and 10-12 GPa, demonstrating that high pressure may be used to synthesise late rare earth derivatives of the recently reported RFeAs(O,F) (R = La-Nd, Sm, Gd) high temperature superconductors.