Temperature and pressure induced lattice dynamics in endohedral and exohedral and exohedral fullerenes

Abstract

Fullerene and its derivatives are potential candidates for thermoelectric applications newlinedue to their low thermal conductivity. This work proposes to utilize the newlineconcept of phonon lattice vibrations of doped fullerenes and fullerene oxides under newlinethermal and mechanical stress that qualitatively alters the heat conduction newlineand the thermoelectric figure-of-merit. newlineThis work presents temperature, laser power and pressure dependent Raman newlinespectral analysis of endohedral metallofulleres (MatC82, M=Gd,Dy) and newlinefullerene oxides (C60O, C70O) to understand their lattice dynamics and thermodynamic newlinestability. The first order temperature and laser power coefficients newlineof Raman frequencies are evaluated and are utilized to evaluate room and high newlinetemperature thermal conductivity. Thermal conductivity of fullerene oxides newlineare smaller the that of Mat C82. Blue-shifts in the Raman frequencies while newlinedecreasing the temperature in metal-cage, C-O and cage internal vibrations newlineof endohedral and exohedral describe thermal contraction in the molecules. newlineTemperature independent linewidth of cage internal vibrations shows minimal newlineanharmonic interaction; whereas, strong temperature dependence metal-cage newlinevibration linewidths are governed by phonon-phonon and electron-phonon coupling. newlineThe density functional measurement has been performed to examine contraction newlinein the C O bond length of C60O. C-O bond contraction has been corroborated newlinewith the experimental Raman shifts at different temperatures and newlinepressures to evaluate the linear expansion coefficient and linear compressibility newlineof C60O. Isobaric mode and isothermal mode Gr¨uneisen parameter are used to newlineexplain the thermodynamic stability of C60O at low temperature and high pressure. newlineThe correlation between Gr¨uneisen parameter and thermal conductivity newlineprovides an insight into pressure induced thermal conductance which in turn newlinemay affects their thermoelectric efficiency. newline