Ying Lei,Yu Li,Lin Xu,Junyou Yang,Rundong Wan,Hongming Long
Nano-structured Half-Heusler TiNiSn thermoelectric bulk was prepared by microwave-assisted rapid solid-state synthesis and sintering. The mixture of powders of Ti, Ni, Sn was cold pressed before being heated by microwave irradiation. A microwave susceptor material rapidly heats the elemental starting materials inside an evacuated quartz tube resulting in near single phase compounds in 4 min 20 s. The synthesized sample was milled for 30 min in an agate mortar and cold pressed for the following sintering. An 86% density of TiNiSn thermoelectric bulk contains ∼100 nm pore and nanocrystal was sintered in 20 min. For TiNiSn bulk, low thermal conductivity of 2–3 W/m·K at temperatures in the range of the room temperature to 773 K. The ZT values of around 0.3 are found, with the microwave-prepared sample displaying noticeable superior properties over conventionally prepared half-Heuslers due to inclusion of nanopore and In-situ nanocrystal.
With excellent high-temperature stability (up to 1000 K) and favorable electrical properties for thermoelectric application, TiNiSn-based half-Heusler (HH) alloys are expected to be promising thermoelectric materials for the recovery of waste heat in the temperature ranging from 700 K to 900 K. However, their thermal conductivity is always relatively high (5–10 W/mK), making it difficult to further enhance their thermoelectric figure-of-merit ( ZT ). In the past decade, introducing nano-scale secondary phases into the HH alloy matrix has been proven to be feasible for optimizing the thermoelectric performance of TiNiSn. In this study, a series of TiNiSn-based alloys have been successfully synthesized by a simple solid-state reaction. The content and composition of the heterogeneous phase (TiNi 2 Sn and Sn) is accurately regulated and, as a result, the thermal conductivity successfully reduced from 4.9 W m −1 K −1 to 3.0 Wm −1 K −1 (750 K) due to multi-scale phonon scattering. Consequently, a ZT value of 0.49 is achieved at 750 K in our TiNiSn-based thermoelectric materials. Furthermore, the thermal stability of TiNiSn alloys is enhanced through reducing the Sn substance phase.
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