Entropy stabilization is a novel materials-design paradigm to realize new compounds with widely tunable properties. However, almost all entropystabilized materials so far are either conducting metals or insulating ceramics, with a clear dearth in the semiconducting regime. Here, a new class of the multicationic and -anionic entropy-stabilized chalcogenide alloys based on the (Ge,Sn,Pb)(S,Se,Te) formula are synthesized and characterized experimentally. The configurational entropy from the disorder of both the anion and the cation sublattices reaches a record value of ∼2.2 R mol −1 for the equimolar composition and stabilizes the singlephase solid solution. Theoretical calculations and experiments both show that the synthesized alloys are thermodynamically stable at the growth temperature and kinetically metastable at room temperature, segregating by spinodal decomposition at moderate temperatures. Doping and electronic transport measurements verify that the synthesized materials are ambipolarly dopable semiconductors, which pave the way for the wider adoption of entropy-stabilized chalcogenide alloys in functional applications.

In this study, n-type Cu and Zn metal nanoparticle decorated Bi₂(Te₀.₉Se₀.₁)₃ ingots were prepared by a large-scale zone melting technique, with the concept of 'nanoparticle-in-alloy' to separately tune the electrical and thermal transport properties. Cu and Zn additions play multiple but different roles in the materials, whereas both of them form metal nanoinclusions embedded in van der Waals gaps or grain boundaries, exerting influences on thermoelectric properties. Cu addition, accommodated in the tetrahedral vacancies formed by four Te(1) atoms, effectively adjusts the electron concentration by donating its valence electron, and appreciably optimizes the power factor. Coupled with the significant frustration of heat-carrying phonons by Cu nanoinclusions, a highest ZT of 1.15 can be achieved for the 1 at.% Cu sample, which is an ∼20% improvement compared with that of commercial halogen-doped ingots. Zn addition, however, acting as weak donor, noticeably increases the density of state effective mass and Seebeck coefficient, and gives rise to a high ZT of 1.1. In particular, the kilogram-grade production technique coupled with the high ZT makes metal nanoparticle decorated n-type materials very promising for commercial applications.

Coherent incorporation of magnetic nanoinclusions into a heavily doped semiconductor leads to overlapping bound magnetic polarons and a drastic reduction of the effective carrier density.

Power electronics seek to improve power conversion of devices by utilizing materials with a wide bandgap, high carrier mobility, and high thermal conductivity. Due to its wide bandgap of 4.5 eV, β-Ga2O3 has received much attention for high-voltage electronic device research. However, it suffers from inefficient thermal conduction that originates from its low-symmetry crystal structure. Rutile germanium oxide (r-GeO2) has been identified as an alternative ultra-wide-bandgap (4.68 eV) semiconductor with a predicted high electron mobility and ambipolar dopability; however, its thermal conductivity is unknown. Here, we characterize the thermal conductivity of r-GeO2 as a function of temperature by first-principles calculations, experimental synthesis, and thermal characterization. The calculations predict an anisotropic phonon-limited thermal conductivity for r-GeO2 of 37 W m−1 K−1 along the a direction and 58 W m−1 K−1 along the c direction at 300 K where the phonon-limited thermal conductivity predominantly occurs via the acoustic modes. Experimentally, we measured a value of 51 W m−1 K−1 at 300 K for hot-pressed, polycrystalline r-GeO2 pellets. The measured value is close to our directionally averaged theoretical value, and the temperature dependence of ∼1/T is also consistent with our theory prediction, indicating that thermal transport in our r-GeO2 samples at room temperature and above is governed by phonon scattering. Our results reveal that high-symmetry UWBG materials, such as r-GeO2, may be the key to efficient power electronics.

Designing crystalline solids in which intrinsically and extremely low lattice thermal conductivity mainly arises from their unique bonding nature rather than structure complexity and/or atomic disorder could promote thermal energy manipulation and utilization for applications ranging from thermoelectric energy conversion to thermal barrier coatings. Here, we report an extremely low lattice thermal conductivity of ∼0.34 W m −1 K −1 at 300 K in the new complex sulfosalt MnPb 16 Sb 14 S 38 . We attribute the ultralow lattice thermal conductivity to a synergistic combination of scattering mechanisms involving (1) strong bond anharmonicity in various structural building units, owing to the presence of stereoactive lone-electron-pair (LEP) micelles and ( 2) phonon scattering at the interfaces between building units of increasing size and complexity. Remarkably, low-temperature heat capacity measurement revealed a C p value of 0.206 J g −1 K −1 at T > 300 K, which is 22% lower than the Dulong−Petit value (0.274 J g −1 K −1 ). Further analysis of the C p data and sound velocity (ν = 1834 m s −1 ) measurement yielded Debye temperature values of 161 and 187 K, respectively. The resulting Gruneisen parameter, γ = 1.65, further supports strong bond anharmonicity as the dominant mechanism responsible for the observed extremely low lattice thermal conductivity.

The integration within the same crystal lattice of two or more structurally and chemically distinct building units enables the design of complex materials featuring the coexistence of dissimilar functionalities. Here...

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Atomic-scale incorporation of CuAlSe 2 inclusions within the Cu 2 Se matrix, achieved through a solid-state transformation of CuSe 2 template precursor using elemental Cu and Al, enables a unique temperature-dependent dynamic doping of the Cu 2 Se matrix. The CuAlSe 2 inclusions, due to their ability to accommodate a large fraction of excess metal atoms within their crystal lattice, serve as a "reservoir" for Cu ions diffusing away from the Cu 2 Se matrix. Such unidirectional diffusion of Cu ions from the Cu 2 Se matrix to the CuAlSe 2 inclusion leads to the formation, near the CuAlSe 2 /Cu 2 Se interface, of a high density of Cu-deficient β-Cu 2−δ Se nanoparticles within the α-Cu 2 Se matrix and the formation of Cu-rich Cu 1+y AlSe 2 nanoparticles with the CuAlSe 2 inclusions. This gives rise to a large enhancement in carrier concentration and electrical conductivity at elevated temperatures. Furthermore, the nanostructuring near the CuAlSe 2 /Cu 2 Se interface, as well as the extensive atomic disorder in the Cu 2 Se and CuAlSe 2 phases, significantly increases phonon scattering, leading to suppressed lattice thermal conductivity. Consequently, a significant improvement in ZT is observed for selected Cu 2 Se/CuAlSe 2 composites. This work demonstrates the use of in situformed interactive secondary phases in a semiconducting matrix as an elegant alternative approach for further improvement of the performance of leading thermoelectric materials.