Hf-doping effect on the thermoelectric transport properties of n-Type Cu_0.01Bi₂Te_2.7Se_0.3

Polycrystalline bulks of Hf-doped Cu_0.01Bi₂Te_2.7Se_0.3 are prepared via a conventional melt-solidification process and subsequent spark plasma sintering technology, and their thermoelectric performances are evaluated. To elucidate the effect of Hf-doping on the thermoelectric properties of n-type Cu_0.01Bi₂Te_2.7Se_0.3, electronic and thermal transport parameters are estimated from the measured data. An enlarged density-of-states effective mass (from ~0.92 m₀ to ~1.24 m₀) is obtained due to the band modification, and the power factor is improved by Hf-doping benefitting from the increase in carrier concentration while retaining carrier mobility. Additionally, lattice thermal conductivity is reduced due to the intensified point defect phonon scattering that originated from the mass difference between Bi and Hf. Resultantly, a peak thermoelectric figure of merit zT of 0.83 is obtained at 320 K for Cu_0.01Bi_1.925Hf_0.075Te_2.7Se_0.3, which is a ~12% enhancement compared to that of the pristine Cu_0.01Bi₂Te_2.7Se_0.3.