Enhancing Thermoelectric Properties through Control of Nickel Interstitials and Phase Separation in Heusler/Half-Heusler TiNi1.1Sn Composites

Abstract

Thermoelectric devices, which allow direct conversion of heat into electrical energy, require materials with improved figures of merit (zT) in order to ensure widespread adoption. Several techniques have been proposed to increase the zT of known thermoelectric materials through the reduction of thermal conductivity, including heavy atom substitution, grain size reduction and inclusion of a semicoherent second phase. The goal in these approaches is to reduce thermal conductivity through phonon scattering without modifying the electronic properties. In this work, we demonstrate that Ni interstitials in the half-Heusler thermoelectric TiNiSn can be created and controlled in order to improve physical properties. Ni interstitials in TiNi1.1Sn are not thermodynamically stable and, instead, are kinetically trapped using appropriate heat treatments. The Ni interstitials, which act as point defect phonon scattering centers and modify the electronic states near the Fermi level, result in reduced thermal conductivity and enhance the Seebeck coefficient. The best materials tested here, created from controlled heat treatments of TiNi1.1Sn samples, display zT = 0.26 at 300 K, the largest value reported for compounds in the Ti–Ni–Sn family.

Magnetic Contribution to the Seebeck Effect

“…Thermoelectricity continues to be a subject of intense research. As energy is clearly a global issue, some scientists are motivated by the search for the largest possible Seebeck coefficient [ 1 , 2 ], and examine the potential of topological metals [ 3 ], while others seek to optimize the material ZT coefficient to attain a thermal efficiency which would be sufficient for widespread applications [ 4 , 5 ]. The anomalous Nernst effect is now an active field of research [ 6 , 7 , 8 ].…”

Substitution Versus Full-Heusler Segregation in TiCoSb

“…The aim of this work was to develop a good p-type thermoelectric material based on TiCoSb that avoids the use of expensive Zr and Hf. Compared to TiNiSn (see e.g., [16][17][18][19][20][21][22][23][24][25]), TiCoSb has attracted far less interest and does not support the presence of interstitial Co for samples prepared using powder routes [26]. Previous work from our group showed that co-substitution with V and Sn improved the high-temperature stability of TiCoSb [26].…”

Characterisation of Misfit Dislocations at Semicoherent Interfaces in Biphasic Functional Heusler Intermetallics

“…Rather than externally applied strain, strain fields can be built in to these systems through phase separation between the full Heusler (fH, XY2Z) phase and the half Heusler (hH, XYZ) phase. Biphasic Heuslers exhibit complex microstructures, which can be tailored to control precipitate shape, size, and volume fraction, ultimately affecting the physical properties of the composite [2,3].…”