Achieving Compatible p/n-Type Half-Heusler Compositions in Valence Balanced/Unbalanced Mg_1-VNiSb

Area of Science:

• Materials Science
• Solid State Physics
• Inorganic Chemistry

Background:

• Half-Heusler (HH) compounds are significant in thermoelectric research due to their potential for energy conversion.
• Developing both p-type and n-type thermoelectric materials with compatible thermal expansion is crucial for fabricating efficient thermoelectric modules.
• High thermal conductivity in conventional HH materials has been a persistent challenge limiting their performance.

Purpose of the Study:

• To demonstrate the p-type to n-type transition in valence-balanced/unbalanced HH compositions by adjusting the Mg:V chemical ratio.
• To investigate the thermoelectric properties of Ti-doped Mg_1-xV_xNiSb, focusing on Seebeck coefficient, power factor, and thermal conductivity.
• To explore the potential of these HH materials for fabricating functional thermoelectric modules.

Main Methods:

• Synthesized Mg_1-xV_xNiSb compositions with varying Mg:V ratios to achieve p-type to n-type transitions.
• Characterized the thermoelectric properties, including Seebeck coefficient and power factor, of Ti-doped Mg_0.57V_0.33Ti_0.1NiSb.
• Measured the lattice thermal conductivity (κ_L) of the synthesized n-type HH compositions.

Main Results:

• Successfully demonstrated the p-type to n-type transition in Mg_1-xV_xNiSb by tuning the Mg:V ratio.
• Achieved a Seebeck coefficient of -130 μV K^-1 and a power factor of 0.4 mW m^-1 K^-2 at 400 K for Ti-doped Mg_0.57V_0.33Ti_0.1NiSb.
• Reported significantly reduced lattice thermal conductivity (κ_L < 2.5 W m^-1 K^-1 at 300 K) for n-type compositions compared to conventional HH materials.
• Fabricated a thermoelectric module with a maximum output power (P_max) of approximately 63 mW at a temperature difference of 390 K.

Conclusions:

• The synthesis of p- and n-type Mg_1-xV_xNiSb compositions with low lattice thermal conductivity offers a promising strategy for high-performance thermoelectric materials.
• Achieving both p- and n-type materials from similar parent compositions facilitates the fabrication of efficient thermoelectric modules.
• Exploring the compositional space of valence-balanced/unbalanced quaternary HH compositions is beneficial for advancing thermoelectric device development.