Improving the thermoelectric performance of TiNiSn half-Heusler via incorporating submicron lamellae eutectic phase of Ti_70.5Fe_29.5: a new strategy for enhancing the power factor and reducing the thermal conductivity

Abstract

The concept of a composite derived by incorporating a second minor phase in bulk thermoelectric materials has established itself as an effective paradigm for optimizing high thermoelectric performance.In this work, the incorporation of submicron lamellae eutectic phases into cheap, abundant and nontoxic TiNiSn half-Heusler is extended for the first time to optimize its thermoelectric performance. HalfHeusler (HH) TiNiSn/eutectic Ti 70.5 Fe 29.5 composites were fabricated by employing the arc-melting route, followed by the spark plasma sintering (SPS) technique. Incorporating the metallic submicron lamellae eutectic phase of Ti 70.5 Fe 29.5 into the HH TiNiSn matrix results in a substantial increase in the power factor ($57% higher than TiNiSn HH) and simultaneous reduction ($25% lower than TiNiSn HH) in the thermal conductivity, leading to an enhanced thermoelectric figure-of-merit (ZT) of 0.41 at 773 K for the half-Heusler (HH) TiNiSn/eutectic Ti 70.5 Fe 29.5 composite with a mass ratio a 33 : 1, which is 105% higher than its counterpart TiNiSn HH. This enhancement in power factor is primarily due to an increase in electrical conductivity, resulting from the inclusion of the metallic Ti 70.5 Fe 29.5 eutectic phase, while the reduction in thermal conductivity can be ascribed to the enhanced phonon scattering by numerous lamellae interfaces of b-Ti and TiFe of the eutectic phase and also their interfaces with the HH phase.The effective value of the thermal conductivity of HH TiNiSn/eutectic Ti 70.5 Fe 29.5 composites, calculated by the effective medium theory in the light of Maxwell-Eucken approximations, matches well with the experimental value of thermal conductivity.

Graphene boosts thermoelectric performance of a Zintl phase compound

“…The decrease in Seebeck coefficient at room temperature is consistent with associated increase in carrier concentration. This phenomenon of inverse relation between a and s can be explained by the equation, 65,89,90 a ¼ AE k B e 2 þ ln 2ð2pm*k B TÞ where m* is the effective mass relating the density of states and n, the carrier concentration. As noted above, the introduction of GNS induces large carrier concentration and hence according to the equation, the a is reduced.…”

Tailoring nanostructured NbCoSn-based thermoelectric materials via crystallization of an amorphous precursor

“…For the intermediate temperature range between 773 and 1073 K, for which abundant industrial waste heat sources are available, lead chalcogenides [10,11], skutterudites [12,13], and half-Heusler compounds [14][15][16] have been intensively studied. Among them, half-Heusler compounds are advantageous in terms of their high thermal stability [17], mechanical robustness [18], high Seebeck coefficients [19,20], high power factor [21], non-toxicity [22], and usage of earth-abundant elements [23]. However, these beneficial properties are compromised by a relatively large lattice thermal conductivity, limiting the figure of merit [24,25].…”

Compositions and thermoelectric properties of XNiSn (X = Ti, Zr, Hf) half-Heusler alloys

“…18 The absence of clear inclusions demonstrates that the degree of segregation is sensitively dependent on the sample processing, which is in keeping with the wide variety of nanostructures reported in the literature. 25 Other approaches aimed at minimising κ lat include off-stoichiometric X 9 Ni 7 Sn 8 (X = Ti, Zr) compositions that form a HH matrix and a number of segregated phases, 26,27 addition of a Ti 70.5 Fe 29.5 eutectic, 28 InSb inclusions in TiCoSb, 29,30 and phase segregation involving mixtures of HH phases. [19][20][21][22][23] Recent studies have linked the low κ to phase segregation into multiple half-Heusler phases with different ratios of X-metals.…”