Doping and temperature dependence of Raman scattering fromNdFeAsO1−xFx(x=0–0.2)superconductor

Raman spectra of superconductor ${\text{NdFeAsO}}_{1\ensuremath{-}x}{\text{F}}_{x}$ $(x=0.0,0.1,0.2)$ compounds have been systematically investigated as functions of temperature and fluorine concentration. It was found that fluorine doping leads to structure disorder of insulator Nd-O layers and detectable downshift as well as increased temperature coefficients of the Fe-As vibrational modes. Additionally, low-temperature Raman measurements reveal that the in-plane phonon modes of the layered compound are unusually more sensitive to temperature change than those along the axis, and this anisotropic temperature dependence of phonon models is further enhanced by fluorine doping.