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 n_H. 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, κ_L, value of 0.77 W m⁻¹K⁻¹, approaching the κ_min 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.