Structure and Thermoelectric Properties Correlation in half-Heusler ZrNiSn- based Bulk Nano-composite Materials by Trans
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1267-DD06-12
Structure and Thermoelectric Properties Correlation in half-Heusler ZrNiSn- based Bulk Nano-composite Materials by Transmission Electron Microscopy D. K. Misra, Julien P. A. Makongo, Michael R. Shabetai, Girija S. Chaubey, John B. Wiley, Kevin L. Stokes, Pierre F.P. Poudeu* Advanced Materials Research Institute, University of New Orleans, Louisiana 70148, USA Louisiana 70148, USA Corresponding author:[email protected] ABSTRACT We report the effects of HfO2 nanoparticles as inclusion to the Zr0.5Hf0.5Ni0.8Pd0.2Sn0.99Sb0.01 half-Heusler matrix on the thermoelectric properties. X-ray powder diffraction and transmission electron microscopy were employed for the phase identification and microstructure characterization of the composites. The transport properties are mainly discussed with regards to the microstructure details. INTRODUCTION The half-Heusler compound ZrNiSn is considered to be a prospective material for thermoelectric conversion and has recently received tremendous interest [1-4].The thermoelectric performance of a material at given temperature is measured by the dimensionless figure of merit ZT = S2T/ρκ, where S is the Seebeck coefficient, and ρ and κ are the electrical resistivity and thermal conductivity, respectively. S2/ρ is known as the power factor. The thermal conductivity consists of two contributions: the lattice thermal conductivity κl and the electronic thermal conductivity κe. The improvement of thermoelectric performance in such materials can be made by reducing the lattice thermal conductivity because lattice thermal conductivity for ZrNiSn-based halfHeusler alloys is much greater than the electronic component. In an attempt to reduce the lattice thermal conductivity of ZrNiSn half-Heusler compound, Uher et al. introduced phonon mass fluctuation scattering by alloying Hf on the Zr site, which led to an overall reduction of the total thermal conductivity [1]. An effect of alloying Hf on Zr site and Pd on Ni site was further studied by several researchers [2-4]; the thermal conductivity at room temperature for Zr0.5Hf0.5Ni0.8Pd0.2Sn0.99Sb0.01 reached 4.5 W/mK. Although, it was significantly reduced with compared to other half-Heusler, the thermal conductivity value is still approximately 3 times higher than that of state-of-art thermoelectric materials such as Bi2Te3- based alloys. Huang et al. [5-6] studied the effect of γ- Al2O3 and ZrO2 nanoparticles on undoped ZrNiSn half-Heusler compound and reported further reduction of approximately 25% in thermal conductivity and hence improved thermoelectric performance. In addition, the partial vacancy occupation of the Co, Sn and Ni atoms was reported in the Ti–Co–Sn [7–9] and Ti–Ni–Sn [10] systems to improve the thermoelectric figure of merit. In the present work, Zr0.5Hf0.5Ni0.8Pd0.2Sn0.99Sb0.01/HfO2 composites were prepared and the effect of HfO2 nanoparticles on the thermopower performance of Zr0.5Hf0.5Ni0.8Pd0.2Sn0.99Sb0.01 half-Heusler compound has been investigated. The microstructure and thermoelectric properties correlation has a
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