Superconducting properties of the oxygen-vacant iron oxyarsenide   TbFeAsO1-x from underdoped to overdoped compositions
  A wide-range doping was achieved by a high-pressure method for TbFeAsO1-x from "under doped" to "over doped" superconducting compositions throughout the optimized superconductivity (Tc of 44 K). Tc vs. lattice constant shows a dome-shaped feature, while Tc vs. the lattice constant likely follows a unique empirical curve over the doping range. The relatively large amount of oxygen vacancies up to 0.3 per the formula unit was introduced possibly because of the smaller replacement Tb than the other Ln (rare-earth element) in the LnFeAsO1-x system. 
Y.G. Shi, S. Yu, A.A. Belik, Y. Matsushita, M. Tanaka, Y. Katsuya, K.   Kobayashi, Y. Hata, H. Yasuoka, K. Yamaura, E. Takay...