High-$T$c Superconductivity and Raman Scattering Study of the phonon properties of electron doped (transition metal, rare-earth) - Oxygen-Free CaFeAsF and compared with RFeAsO system.

Quaternary CaFeAsF has ZrCuSiAs-type structure,(RO)$^{\mathrm{\delta +}}$ layer in RFeAsO replaced by (CaF)$^{\mathrm{\delta +}}$ layer,with tetragonal ($P$4/\textit{nmm})-orthorhombic (\textit{Cmma}) phase transition at 134K,while magnetic order,SDW sets in at 114K. Partial replacement of Fe with Co/Ni is direct electron doping to (FeAs)$^{\mathrm{\delta +}}$ layer.Tc \textasciitilde 15K in CaFe$_{\mathrm{0.9}}$Ni$_{\mathrm{0.1}}$AsF.Substitution of rare earth metal for alkaline earth metal suppresses anomaly in resistivity {\&} induces superconductivity.Tc \textasciitilde 52K in Ca$_{\mathrm{0.5}}$Pr$_{\mathrm{0.5}}$FeAsF.Characterized by resistivity, susceptibility,XRD {\&} EDX-SEM.Upper critical field estimated from magneto resistance.Bulk superconductivity proved by DC magnetization. Hall coefficient R$_{\mathrm{H}}$ revealed hole-like charge carriers in parent compound CaFeAsF, while electron-type (R$_{\mathrm{H}}$ in normal state is --Ve) for Ca$_{\mathrm{0.5}}$Pr$_{\mathrm{0.5}}$FeAsF.Evolution of Raman active phonons of Ca$_{\mathrm{1-x}}$Pr$_{\mathrm{x}}$FeAsF measured with polarized Raman spectroscopy at room temperature from \textit{ab }surfaces of impurity-free microcrystals.Spectra exhibit sharp phonon lines on very weak electronic scattering background.Frequency and symmetry of Raman phonons involving out-of-plane atomic vibrations are found at 162.5 cm$^{\mathrm{-1}}$ ($A$1$g$, Pr), 201 cm$^{\mathrm{-1}}$ ($A$1$g$, As), 215.5 cm$^{\mathrm{-1}}$ ($B$1$g$, Fe), 265 cm$^{\mathrm{-1}}$ (\textit{Eg}, Fe) and 334 cm$^{\mathrm{-1}}$ ($B$1$g$, F) for Ca$_{\mathrm{0.5}}$Pr$_{\mathrm{0.5}}$FeAsF.Observations are compared with RFeAsO unconventional superconductors also possibly related to magnetic fluctuations