Interpreting the Combustion Process for High-Performance ZrNiSn Thermoelectric Materials

Abstract

The ZrNiSn alloy, a member of the half-Heusler family of thermoelectric materials, shows great potential for mid-to-high-temperature power generation applications due to its excellent thermoelectric properties, robust mechanical properties, and good thermal stability. The existing synthesis processes of half-Heusler alloys are, however, rather time and energy intensive. In this study, single-phase ZrNiSn bulk materials were prepared by self-propagating high-temperature synthesis (SHS) combined with spark plasma sintering (SPS) for the first time. The analysis of thermodynamic and kinetic processes shows that the SHS reaction in the ternary ZrNiSn alloy is different from the more usual binary systems. It consists of a series of SHS reactions and mass transfers triggered by the SHS fusion of the binary Ni-Sn system that eventually culminates in the formation of single-phase ternary ZrNiSn in a very short time, which reduced the synthesis period from few days to less than an hour. Moreover, the nonequilibrium feature induces Ni interstitials in the structure, which simultaneously enhances the electrical conductivity and decreases the thermal conductivity, which is favorable for thermoelectric properties. The maximum thermoelectric figure of merit ZT of the SHS + SPS-processed ZrNiSnSb alloy reached 0.7 at 870 K. This study opens a new avenue for the fast and low-cost fabrication of half-Heusler thermoelectric materials.

Looking for new thermoelectric materials among TMX intermetallics using high-throughput calculations

“…and D.O.S(HfCoP) = 0.38 states/eV-f.u.). In particular, ZrNiSn illustrates the need of flexible criterion as its DOS differs from 0 at the Fermi level while it is reported [33][34][35] as a semiconductor.…”

Advances in half-Heusler alloys for thermoelectric power generation

“…59,63,64 Other means of achieving reaction include microwave synthesis and self-propagating combustion synthesis. [65][66][67][68][69] After initial reaction it is common to anneal the sample, typically between 900-1000 °C, to equilibrate the sample and increase homogeneity. In the past couple of years however, what may be called 'out-of-equilibrium' processing has gained much prominence.…”

“…87 Self-propagating synthesis for exothermic processes allows for the heat produced from initial reaction to drive the reaction to completion, as has been demonstrated for ZrNiSn. 66,69 In a custom pressing setup, the heat released from the reaction (initiated by Tungsten electrode) was enough to densify the pellet, with a T max = 1668 K achieved by the self-propagating reaction. 66 The large literature pool also allows for comparisons to be made in how the HH phases form, which is important when planning microstructure and defects.…”

Thermoelectric power generation: from new materials to devices

“…We will discuss this in detail later. In addition, some facile and costefficient fabrication methods (self-propagating high-temperature synthesis, thermal combustion, laser) have been developed to prepare HH alloys [132][133][134], which point to a reasonable path to scalability [24,110,123,127]. All these advances clearly demonstrate the great potential of HH alloys for high-temperature thermoelectric power generation.…”