Achieving Densification and High Thermoelectric Performance in TiNiSn-Based Alloys with a MoO₃ Sintering Aid

Area of Science:

• Materials Science
• Thermoelectrics
• Nanocomposites

Background:

• Hafnium-free half-Heusler (HH) alloys are promising thermoelectric materials.
• Optimizing density and thermal transport is crucial for enhancing thermoelectric performance.
• Molybdenum trioxide (MoO3) as a sintering aid offers potential multifunctional benefits.

Purpose of the Study:

• To investigate the effect of MoO3 addition on the thermoelectric properties of Hf-free TiNi0.94Cu0.06Sn.
• To enhance the density and carrier mobility of the alloy using MoO3 as a sintering aid.
• To decouple electrical and thermal transport for improved figure of merit (zT).

Main Methods:

• Preparation of TiNi0.94Cu0.06Sn-x wt % MoO3 composites via hot-pressing sintering.
• Characterization of material density, carrier mobility, Seebeck coefficient, electrical conductivity, and thermal conductivity.
• Analysis of power factor and figure of merit (zT) at elevated temperatures.

Main Results:

• Trace MoO3 additions significantly increased alloy density (98.49% to 99.95%) and doubled room-temperature carrier mobility.
• An optimal MoO3 composition (x=0.75) yielded a peak power factor of 45 × 10^-4 W m^-2 K^-2.
• Total thermal conductivity was minimized to 3.81 W m^-1 K^-1 at x=1, a ~21% decrease, due to reduced lattice contribution from phonon scattering.
• A maximum figure of merit (zT) of 0.89 at 800 K was achieved, representing a 29% enhancement.

Conclusions:

• Molybdenum trioxide acts as an effective multifunctional sintering aid, enhancing densification and carrier mobility.
• MoO3 addition introduces multiscale phonon scattering, significantly reducing lattice thermal conductivity.
• The optimized thermoelectric performance, with a 29% increase in zT, positions these Hf-free HH nanocomposites competitively.