Composites of Bi2–xSbxTe3 nanocrystals and fullerene molecules for thermoelectricity

New nanocomposite thermoelectric material composed from nanocrystallites of Bi–Sb–Te alloys covered by C60 molecules has been synthesized and studied. An increase of fullerene content leads to the growth of hole concentration in p-type materials and reduction of electron concentration in n-type materials. The fullerene molecules provide additional scattering of phonons reducing lattice heat conductivity. Reduction of heat conductivity exceeds the reduction of electrical conductivity for fullerene content less than 0.5 volume % and essential enhances the thermoelectric figure of merit. The maximum value of thermoelectric figure of merit equals to 1.17 at 450 K was observed in Bi0.5Sb1.5Te3 composite containing 0.5 volume % C60 molecules. The experimental results were analyzed in a frame of the model based on the Boltzmann equation. The analysis considers light and heavy electrons and holes and accounts the intervalley scattering of charge carriers. The calculations of the kinetic coefficients shows that the improvement of the thermoelectric figure of merit originates from the reduction of the lattice heat conductivity caused by fullerene molecules. The dependencies of the thermoelectric figure of merit on the acceptor concentration were calculated. - Graphical abstract: New nanocomposite thermoelectric material composed from nanocrystallites of Bi–Sb–Te alloys covered by C60 molecules has been synthesized and studied. An increase of fullerene content leads to the growth of hole concentration in p-type materials and reduction of electron concentration in n-type materials. The fullerene molecules provide additional scattering of phonons reducing lattice heat conductivity and enhances the thermoelectric figure of merit. The maximum value of thermoelectric figure of merit equal to 1.17 at 450 K was observed in Bi0.5Sb1.5Te3 composite containing 0.5 volume % fullerene molecules. Simulations of thermoelectric properties were made in frame of four bands, 12 valleys Boltzmann equation approach. Simulated and measured temperature dependencies of thermoelectric properties were compared to get unknown model parameters. These parameters were used to calculate dependencies of thermoelectric properties on acceptor concentration. Calculated dependencies of thermoelectric figure of merit on acceptor concentration are presented in the figure for p-type composites with 0 vol.% C60 (solid lines) and 0.5 vol.% C60 (dashed lines). Highlights: ► C60 doping of Bi–Sb–Te has acceptor effect. ► Fullerene molecules prevent recrystallization in Bi–Sb–Te nanocomposites. ► C60 in Bi–Sb–Te nanocomposites essentially reduces lattice thermal conductivity. ► Thermoelectric figure of merit in nanocomposite C60–Bi–Sb–Te enhanced.