Evidence of improvement in thermoelectric parameters of n-type Bi2Te3/graphite nanocomposite

Abstract

Improvement in thermoelectric parameters is reported with graphite incorporation in n-type Bi2Te3/graphite nanocomposite systems. In-depth thermoelectric properties of nanostructured Bi2Te3/graphite composites are probed both microscopically and macroscopically using x-ray diffraction, Raman spectroscopy, inelastic neutron scattering, and measurement of the temperature dependence of thermal conductivity κ, Seebeck coefficient S, resistivity ρ, and carrier concentration nH. Raman spectroscopic analysis confirms that graphite introduces defects and disorder in the system. Graphite addition induces a large (∼17%) decrease of κ, originating from a strong phonon scattering effect. A low lattice thermal conductivity, κL, value of 0.77 W m−1 K−1, approaching the κmin value, estimated using the Cahill–Pohl model, is reported for Bi2Te3 + 1.0 wt. % graphite sample. Graphite dispersion alters the low-energy inelastic neutron scattering spectrum providing evidence for modification of the Bi2Te3 phonon density of states. Improvement in other thermoelectric parameters, viz., Seebeck coefficient and resistivity, is also reported. Theoretical modeling of electrical and thermal transport parameters is carried out and a plausible explanation of the underlying transport mechanism is provided assuming a simple model of ballistic electron transport in 1D contact channels with two different energies.