Pressure-Induced Modification of Crystal Structure in NdFeAsO1-y (1-y=0.85), Accompanied by Remarkable Suppression of T-c

The atomic positions of the title. oxypnictide compound under pressure were determined by Rietveld analysis of synchrotron X-ray diffraction data. Hydrostatic pressure has effects on the crystal structure in two points: (i) nearly isotropic compression of each of the Fe-As and Nd-O layers at the rate of similar to 0.2%/GPa and (ii) outstanding shrinkage of the interlayer spacing (defined as the distance between adjacent As and Nd planes in this paper) at the rate of similar to 0.7%/GPa. Remarkable suppression of 7,, by hydrostatic: pressure would originate from the change in the electronic structure caused by the modification of the crystal structure. The possible origins will be discussed.