Evidence of structural phase transition in superconducting   SmFeAsO_(1-x)F_x from 19^F NMR
  We report the resistivity, magnetization and 19^F NMR results in polycrystalline sample of SmFeAsO_(0.86)F_(0.14). The resistivity and the magnetization data show a sharp drop at 48 K indicating the superconducting transition. The nuclear spin-lattice rate (1/T_1) and spin-spin relaxation rate (1/T_2) clearly show the existence of a structural phase transition near 163 K in the sample which also undergo superconducting transition. This finding creates interest to explore whether this is unique for only Sm based systems or it is also present in other rare-earth based 1111 superconductors. 
M. Majumder, K. Ghoshray, C. Mazumdar, A. Poddar, A. Ghoshray, D.   Berardan, N. Dragoe
cond-mat.supr-con cond-mat.str-el