Simultaneous increase in thermopower and electrical conductivity through Ta-doping and nanostructuring in half-Heusler TiNiSn alloys

Karati, A and Mukherjee, S and Mallik, RC and Shabadi, R and Murty, BS and Varadaraju, UV (2019) Simultaneous increase in thermopower and electrical conductivity through Ta-doping and nanostructuring in half-Heusler TiNiSn alloys. In: Materialia, 7 .

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Abstract

A new series of Ta-doped Ti1− xTaxNiSn (x = 0–0.05) were synthesized through mechanical alloying (MA) followed by spark plasma sintering (SPS) for the first time. MA for 5 h gave rise to Ti/Ti+Ta and Ni3Sn4 phases. With increasing milling time and subsequent SPS, half-Heusler phase formed along with Ni3Sn4 and TiC as secondary phases. To see the effect of temperature on the density of TiNiSn pellets, SPS was carried out at 1073, 1173 and 1273 K. Sintering of TiNiSn at 1073 K produced full-Heusler (TiNi2Sn) and Ni3Sn4as secondary phases and the pellets had long continuous pores. In contrast, SPS at 1273 K gave rise to increased volume fraction of TiNi2Sn impurity phase with almost no porosity. Thus, SPS conditions were set with respect to optimized densification (95 %) and volume fraction of secondary phases (19 %) at 1173 K for 5 h MA of TiNiSn. Ta-doping is expected to decrease the thermal conductivity and improve the ZT of the alloys. The Ta-doped TiNiSn samples were subsequently milled for 5 h and SPS were carried out for them at 1173 K. Increase in Thermopower and electrical conductivity were observed with increasing temperature for all the samples. Due to the simultaneous improvement in electrical conductivity and Thermopower, a maximum power factor of 1.12 and 2.57 mWm−1K−2 at 830 K were observed for TiNiSn and Ti0.95Ta0.05NiSn sintered at 1173 K, respectively. Due to reduced lattice thermal conductivity of 1.8 and 3 Wm−1K−1 for TiNiSn and Ti0.95Ta0.05NiSn sintered at 1173 K, respectively, maximum ZT of 0.17 and 0.31 were obtained at 823 K.

Item Type:	Journal Article
Publication:	Materialia
Publisher:	Elsevier B.V.
Additional Information:	The copyright for this article belongs to Elsevier B V.
Keywords:	Binary alloys; Electric conductivity; Intermetallics; Mechanical alloying; Microscopic examination; Milling (machining); Nanocrystals; Pelletizing; Spark plasma sintering; Temperature; Ternary alloys; Thermal conductivity of solids; Thermoelectric power; Thermoelectricity; Titanium carbide; Volume fraction, Effect of temperature; Electrical conductivity; Increasing temperatures; Lattice thermal conductivity; Mechanical alloying and milling; Nano-crystalline structures; Thermoelectric properties; Various, Tantalum alloys
Department/Centre:	Division of Interdisciplinary Sciences > Interdisciplinary Centre for Energy Research Division of Physical & Mathematical Sciences > Physics
Date Deposited:	07 Jan 2023 05:19
Last Modified:	07 Jan 2023 05:19
URI:	https://eprints.iisc.ac.in/id/eprint/78851

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