2 research outputs found
Enhanced Thermoelectric Performance in the SrTi<sub>0.85</sub>Nb<sub>0.15</sub>O<sub>3</sub> Oxide Nanocomposite with Fe<sub>2</sub>O<sub>3</sub>‑Functionalized Graphene
Doped SrTiO3 is considered
one of the potential
thermoelectric
(TE) candidates but its TE figure of merit, ZT needs
to be improved for practical application of electricity generation
from high-grade waste-heat. In the present work, enhanced TE performance
has been realized for SrTi0.85Nb0.15O3 (STN) perovskite adopting the strategy of composite formation with
Fe2O3-functionalized graphene (FGR). We have
achieved a maximum electrical conductivity of 1.4 × 105 S m–1 for 1 wt % FGR added to STN, which is around
1185% larger than that of pristine STN. The presence of FGR in the
STN matrix acts as a mobility booster of electrons, overcoming the
effect of Anderson localization of electrons, which impedes the electron
transport in STN. This is evident from the order of magnitude increase
in weighted mobility of STN after FGR addition. Furthermore, the incorporation
of FGR causes about a 34% decrease in the lattice thermal conductivity.
The Debye–Callaway model demonstrates that the phonon–phonon
Umklapp scattering is primarily responsible for reduced thermal conductivity.
The presence of FGR sheets along the grain boundaries of STN, Fe2O3 nanoparticles, and lattice imperfections gives
rise to the glass-like temperature-independent phonon mean-free-path,
especially above Debye temperature. The maximum ZT ∼ 0.57 has been obtained at 947 K for the 1 wt % FGR sample,
which is around 420% higher than that of pristine STN. Furthermore,
we have fabricated a prototype of a four-legged n-type TE module,
demonstrating one of the highest power outputs of 18 mW among reported
oxide thermoelectrics
Low Lattice Thermal Conductivity in a Wider Temperature Range for Biphasic-Quaternary (Ti,V)CoSb Half-Heusler Alloys
Intrinsically high lattice thermal conductivity has remained
a
major bottleneck for achieving a high thermoelectric figure of merit
(zT) in state-of-the-art ternary half-Heusler (HH)
alloys. In this work, we report a stable n-type biphasic-quaternary
(Ti,V)CoSb HH alloy with a low lattice thermal conductivity κL ≈ 2 W m–1 K–1 within
a wide temperature range (300–873 K), which is comparable to
the reported nanostructured HH alloys. A solid-state transformation
driven by spinodal decomposition upon annealing is observed in Ti0.5V0.5CoSb HH alloy, which remarkably enhances
phonon scattering, while electrical properties correlate well with
the altering electronic band structure and valence electron count
(VEC). A maximum zT ≈ 0.4 (±0.05) at
873 K was attained by substantial lowering of κL and
synergistic enhancement of the power factor. We perform first-principles
density functional theory calculations to investigate the structure,
stability, electronic structure, and transport properties of the synthesized
alloy, which rationalize the reduction in the lattice thermal conductivity
to the increase in anharmonicity due to the alloying. This study upholds
the new possibilities of finding biphasic-quaternary HH compositions
with intrinsically reduced κL for prospective thermoelectric
applications