Fabrication and characterization of nickel contacts for magnesium silicide based thermoelectric generators

Abstract

a b s t r a c tMagnesium silicide based solid solutions are highly attractive materials for thermoelectric energy harvesting due to their abundance and excellent thermoelectric properties. Identification and testing of suitable contacts is -besides material optimization -the major challenge in the development of thermoelectric modules. We have applied Ni contacts on doped Mg 2 Si samples using a simple one-step sintering technique. These contacts were analyzed by combining microstructural analysis with spatially resolved and temperature dependent contact resistance measurements. We observe very good adhesion, homogeneous and low contact resistances <10 lX cm 2 . as well as good stability with temperature. Three different approaches for determining the contact resistances are compared and the respective errors are discussed.

Thermoelectric transport and microstructure of optimized Mg2Si0.8Sn0.2

“…Moreover, as Mg 2 Si is thermally and chemically more stable than Mg 2 Sn it is plausible that Sirich compositions are more stable than Sn-rich compositions, allowing operation at higher temperatures. Furthermore, Mg 2 Si 0.8 Sn 0.2 is closer to the technologically more developed Mg 2 Si, where progress in contact development has been reported 13,14 . On the other hand, compared to Mg 2 Si an improvement of the thermoelectric properties can be expected due to increased phonon alloy scattering.…”

High efficiency Mg2(Si,Sn)-based thermoelectric materials: scale-up synthesis, functional homogeneity, and thermal stability

“…The best performing materials in the Mg 2 (Si,Sn) system usually contain $23 AE 3 at% Sn, which is where the conduction band convergence is taking place, 41,42 and all exhibit a maximum gure of merit, zT max , of 1.4 AE 0.2, satisfactory for the device applications. 43 As for industrial applications, in addition to the electrode development which is in good progress, [44][45][46] a large amount of material is required; thus, a scalable synthesis method that sustains the outstanding TE properties of the material needs to be established. The up-scaling process can be challenging due to occurrence of de-mixing phenomena such as the formation of Si-rich and Sn-rich regions induced by gravity.…”

Recent progress in magnesium-based thermoelectric materials

“…For example, n-type Mg 2 Si 0.3 Ge 0.05 Sn 0.65 boasts a zT at ~750 K of 1.4 while p-type Mg 2 Ge 0.4 Sn 0.6 only reaches a maximum zT of 0.5 at around the same temperature. Despite the low efficiency of p-type Mg-based thermoelectric materials, some preliminary results on device design and construction of devices based on these materials has already been achieved 15,16,58,[121][122][123][124] . The low performance of the ptype Mg-based thermoelectric materials creates serious limitations on the construction of devices, and most reports on the use of these materials in modules are on n-type legs 15,58,121 .…”