The Hall and Seebeck coefficients, electrical resistivity, and thermal conductivity of polycrystalline NiSi3P4 were characterized from 2 to 775 K. Undoped NiSi3P4 behaves like a narrow gap semiconductor, with activated electrical resistivity ρ below room temperature and a large Seebeck coefficient of ∼400 μV/K at 300 K. Attempts to substitute boron for silicon resulted in the production of extrinsic holes, yielding moderately dopedsemiconductor behavior with ρ increasing with increasing temperature above ∼150 K. Hall carrier densities are limited to approximately 5 × 1019 cm−3 at 200 K, which would suggest the solubility limit of boron is reached if boron is indeed incorporated into the lattice. These extrinsic samples have a Hall mobility of ∼12 cm2/V/s at 300 K, and a parabolic band equivalent effective mass of ∼3.5 times the free electron mass. At 700 K, the thermoelectric figure of merit zT reaches ∼0.1. Further improvements in thermoelectric performance would require reaching higher carrier densities, as well as a mechanism to further reduce the lattice thermal conductivity, which is ∼5 W/m/K at 700 K. Alloying in Ge results in a slight reduction of the thermal conductivity at low temperatures, with little influence observed at higher temperatures.
Received 14 January 2013Accepted 25 February 2013Published online 13 March 2013
This research was supported by the U. S. Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division (A.F.M., M.A.M), and the US Department of Energy, EERE, Vehicle Technologies, Propulsion Materials Program (H.W.).
Article outline: I. INTRODUCTION II. METHODS III. RESULTS AND DISCUSSION A. Summary