Guided
by the concept of “phonon-liquid electron-crystal”,
many n-type argyrodite compounds have been developed as candidates
for thermoelectric (TE) materials. In recent years, the p-type Cu8GeSe6 (CGS) compound has attracted some attention
in TEs due to the presence of very strong atomic vibrational arharmonicity
inside the sublattice, which is caused by the weak bonding between
Cu ions and [GeSe6]8–. However, its TE
performance is still poor, with a ZT value of only
0.2 at 623 K. Therefore, in this work, we propose to engineer both
the electronic and phonon transports in CGS by incorporating the species
In2Te3. This strategy tunes the carrier concentration
and at the same time increases the phonon scattering on the point
defects (InGe, Ininterstitial, and TeSe) and randomly distributed tetrahedra ([InSe4]5– and [GeTeSe3]4–). As a result, the
phase transformation at 329 K in CGS is eliminated, and the peak ZT value is enhanced from 0.27 for CGS to ∼0.92 for
(Cu8SnSe6)0.9(In2Te3)0.1 at 774 K; this thus proves that the incorporation
of In2Te3 in CGS is an effective way of regulating
its TE performance.
The
argyrodite compound, Ag8SnSe6 (ATS),
which is one of the promising thermoelectric (TE) candidates, is receiving
growing attention in thermoelectrics recently. However, its TE performance
is still low and phases are unstable as the temperature varies. In
this work, inspired by entropy engineering, we eliminate the β/γ
phase transformation at ∼355 K via alloying Ga, thus extending
its high-temperature cubic phase from 320 to 730 K. In the meantime,
the power factor (PF) enhances by 10% and lattice thermal conductivity
(κL) reduces by 40% at 723 K. As a result, the ZT value is boosted to ∼1.15 for Ag8Sn0.5Ga0.5Se6, which stands high among
the ATS systems. This proves that the entropy engineering is an effective
approach to extend the high-temperature range for the cubic γ-phase
and improve its TE performance simultaneously.
In this work, we design and synthesize a hybrid structure consisting of Sn-incorporated Cu3SbSe4 and a second phase CuSe, that is, (Cu3Sb1 − xSnxSe4)(CuSe)y (x = 0–0.04, y = 0.3–0.08), and explore the role of each phase on the improvement of the thermoelectric (TE) performance. In the Cu3Sb1 − xSnxSe4 phase, the element Sn residing at the Sb site provides p-type holes while at the same time increasing the point defects and crystal structure distortion. The presence of the second phase CuSe, which is in situ formed within the Cu3Sb1 − xSnxSe4 matrix, not only improves the electrical conductivity but also increases the phonon scattering on the phase boundaries. As a result, the hybrid structure allows the improvement in TE performance with the highest ZT value of 0.37 at ∼600 K for the samples at x = 0.02–0.03 and y = 0.11–0.09, which is about 42% higher than that of pristine Cu3SbSe4. This work reveals us a new method of improving TE performance, that is, through organizing a hybrid structure in Cu3SbSe4-based composites.
AgBiSe2 is a promising thermoelectric (TE) candidate because of its intrinsically low thermal conductivity (κ = 0.4–0.5 W K−1 m−1 at ∼770 K) and optimal n-type carrier concentration (5.85 × 1018 cm−3 at 300 K). However, its TE figure of merit (ZT) is still low (0.3 at ∼770 K). Therefore, it is necessary to further improve its ZT. In this work, the solid solutions (AgBiSe2)1−x(Ag2Te)x (x = 0–0.125) have been designed through simple alloying Ag2Te inspired by the entropy engineering concept, and the TE performance has been further regulated. The analyses show that the exothermic effects related to α/β and β/γ phase transitions weaken, and the transition temperature of β/γ decreases as the Ag2Te content increases, which indicates the stabilization of the cubic γ-phase at high temperatures. Aside from that, the power factor (PF) enhances from 2.91 μW/cm K2 (x = 0) to 3.49 μW/cm K2 (x = 0.075), and at the same time, the lattice thermal conductivity reduces from 0.3 W K−1 m−1 to 0.1 W K−1 m−1 at ∼760 K. This directly improves the TE performance with the highest ZT value of 1.0, which is almost double that of the pristine AgBiSe2. The result suggests that the entropy engineering is a very effective screening method in thermoelectrics.
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