Generic Approach for Contacting Thermoelectric Solid Solutions: Case Study in n- and p-Type Mg₂Si_0.3Sn_0.7

Abstract

Metallization (known as contacting) of thermoelectric (TE) legs is vital to the long-term performance of a TE device. It is often observed that the compositional changes in a TE solid solution may render a given contact material unsuitable due to a mismatch in the thermal expansion coefficient values. Finding suitable contact materials for TE solid solutions (which often are the best TE materials) remains a challenge. In this work, we propose a multilayer single-step approach in which the same combination of contact materials can be used for a wide compositional range in a solid solution. The outer layer is a metal foil, which helps in creating an Ohmic contact with the interconnects. The intermediate layer is a mixture of the TE material and a metal powder, which results in the formation of the diffusion barrier. The innermost layer is the TE material, which is the active component of the device. The strategy was applied on n- and p-doped Mg2Si0.3Sn0.7 with elemental Cu and Ni providing the desired interface functionalities. Single-step compaction was carried out using the monoblock sintering technique. Microscopic investigation reveals the formation of a well-bonded crack-free interface. Various intermetallic phases were identified at the interface, and the formation of the MgNi2Sn phase was found to be critical to prevent any interdiffusion of elements. Electrical contact resistance (r c) measurements were conducted, and low values of 3 and 19 μΩ cm2 were measured in n- and p-type legs, respectively. The contacted TE legs were further annealed at 400 °C for 7 days to check their stability. Microstructural and electrical resistance measurements reveal minimal changes in the interface layer and r c values, indicating the workability of the multilayer technique.

A Constant Properties Model for the Performance Estimation in Segmented Thermoelectric Generator Elements and Its Experimental Validation Using an n-Type Mg2Si0.3Sn0.7–Bi2Te2.7Se0.3 Segmented Leg

“…The mixed layer contains equal proportions of Ni and TE material for Mg 2 (Si 0.3 Sn 0.7 ) 0.98 Bi 0.02 . Ni has been reported to be an effective diffusion barrier for both Mg 2 (Si 0.3 Sn 0.7 ) 0.98 Bi 0.02 and Bi 2 (Te 2.7 Se 0.3 ) 0.98 (CuI) 0.02 . However, the bond strength of Ni contacts on Bi 2 (Te 2.7 Se 0.3 ) 0.98 (CuI) 0.02 was not promising and the contacts were often delaminated during dicing.…”

Highly Stable Metal─Na0.02Pb0.98Te Contacts for Medium Temperature Thermoelectric Devices

“…Interlayers composed of M + SnTe and SnTe were used to minimize the CTE mismatch and improve the reaction between M (Co and Fe) and Na 0.02 Pb 0.98 Te. Studies on GeTe, Mg 2 (Si, Sn), and CoSb 3 demonstrate that this approach is successful in making stable contacts. Co/Co + 75 vol % SnTe/SnTe/Na 0.02 Pb 0.98 Te (CTE19.3 × 10 –6 K –1 ) and Fe/Fe + 75 vol % SnTe/SnTe/Na 0.02 Pb 0.98 Te (CTE19.4 × 10 –6 K –1 ) hot pressed compacts were free of any visible defects.…”

“…9,10 Contact design demands a suitable interlayer array between the electrode and TE material that can minimize the CTE mismatch and "poisoning" effects. For example, a Si composite layer between W/p-Si 80 Ge 20 B 0.6 , 10 a mixed layer of Fe with n-PbTe (50:50 vol %) for n-PbTe, 11 and a mixed Ni + TE material layer for Cu/Mg 2 (Si, Sn) 12 shows promising contacts.…”

“…Because the choice of electrode materials is often limited due to the above two aspects, alloys and composites whose stoichiometry is tuned to match the TE material’s CTE were often explored. , Contact design demands a suitable interlayer array between the electrode and TE material that can minimize the CTE mismatch and “poisoning” effects. For example, a Si 3 N 4 composite layer between W/p-Si 80 Ge 20 B 0.6 , a mixed layer of Fe with n - PbTe (50:50 vol %) for n - PbTe, and a mixed Ni + TE material layer for Cu/Mg 2 (Si, Sn) shows promising contacts.…”

Interface Engineering Boosting High Power Density and Conversion Efficiency in Mg2Sn0.75Ge0.25‐Based Thermoelectric Devices

“…Since 2012, numerous efforts have explored the use of Ni, [37][38][39][40][41][42][43][44] Cu, [45] Ag, [44] and Al [46,47] as the TEiMs for Mg 2 (Si, Sn)based TEG devices. Several TEiMs comprising multi-element alloys, such as (Co, Cr, Ti)Si 2 , [38] Ni 45 Cu 55 , [48] 304 stainless steel (304SS), [45] Mg 2 SiNi 3 , [49,50] and Ni+TEcM [51] have been reported, exhibiting lower 𝜌 c values. Nevertheless, the 𝜌 c would rebound (> 10 μΩ cm 2 ) after power generation service, [45,46,49,52] even though it was initially reduced from 10000 to 10 μΩ cm 2 , indicating that the interfacial diffusion or reactions may still occur.…”