We report the temperature dependent x-ray powder diffraction of the quaternary compound NdOFeAs (also called NdFeAsO) in the range between 300 and 95K. We have detected the structural phase transition from the tetragonal phase, with P4/nmm space group, to the orthorhombic or monoclinic phase, with Cmma or P 112/n (or P 2/c) space group, over a broad temperature range from 150 to 120K, centered at T0∼137K. Therefore the temperature of this structural phase transition is strongly reduced, by about ∼30K, by increasing the internal chemical pressure going from LaOFeAs to NdOFeAs. In contrast, the superconducting critical temperature increases from 27 to 51K going from LaOFeAs to NdOFeAs doped samples. This result shows that the normal striped orthorhombic Cmma phase competes with the superconducting tetragonal phase. Therefore by controlling the internal chemical pressure in new materials it should be possible to push toward zero the critical temperature T0 of the structural phase transition, giving the striped phase, in order to get superconductors with higherTc.
ASJC Scopus subject areas
- Physics and Astronomy (miscellaneous)
- Condensed Matter Physics
- Electronic, Optical and Magnetic Materials