Analysis of Ce‐ and Yb‐Doped TAGS‐85 Materials with Enhanced Thermoelectric Figure of Merit

Abstract Doping of TAGS‐85 with 1 at% Ce or Yb forms a dilute magnetic semiconductor system with non‐interacting localized magnetic moments that obey the Curie law. X‐ray diffraction patterns and slight broadening in ¹²⁵Te NMR, attributed to paramagnetic effects, suggest that Ce and Yb atoms are incorporated into the lattice. ¹²⁵Te NMR spin‐lattice relaxation and Hall effect show similar hole concentrations of ≈10²¹ cm⁻³. At 700 K, the electric conductivity of the Ce‐ and Yb‐doped samples is similar to that of neat TAGS‐85, while the thermal conductivity and the Seebeck coefficient are larger by 6% and 16%, respectively. Possible mechanisms responsible for the observed increase in thermopower may include i) formation of resonance states near the Fermi level and ii) carrier scattering by lattice distortions and/or by paramagnetic ions. Due to the increase in the Seebeck coefficient up to 205 μV K⁻¹, the thermoelectric power factor of Ce‐ and Yb‐doped samples reaches 36 μW cm⁻¹ K⁻², which is larger than that measured for neat TAGS‐85, 27 μW cm⁻¹ K⁻². The increase in the Seebeck coefficient overcomes the increase in the thermal conductivity, resulting in a total increase of the figure of merit by ≈25% at 700 K compared to that observed for neat TAGS‐85.