Despite extensive research, much of PbSnTeSe alloying space is unexplored. High-throughput bulk synthesis augments literature with high-resolution (121 sample) property maps.

Phase boundary mapping in Cu2HgGeTe4 allows discovery of Hg2GeTe4 and further enables carrier density control over 4 orders of magnitude.

Ternary diamond-like semiconductors, such as CuInTe2, are known to exhibit promising p-type thermoelectric performance. However, the interplay between growth conditions, native defects, and thermoelectric properties have limited their realization. First-principles calculations of CuInTe2 indicate that the electronic properties are controlled by three dominant defects: VCu, CuIn, and InCu. The combination of these low-energy defects with significant elemental chemical potential phase space for CuInTe2 yields a broad phase width. To validate these calculations, polycrystalline, bulk samples were prepared and characterized for their structural and thermoelectric properties as a function of stoichiometry. Collectively, the off-stoichiometric samples show a range of carrier concentrations that span 5 orders of magnitude (1015 to 1019 h+ cm–3). Mobility of the off-stoichiometric samples suggests that copper vacancies act as strongly scattering point-defect sites, while the other native defects scatter less strongly. Such vacancy scattering extends to the thermal conductivity where a reduction in κL is observed and contributes to enhanced thermoelectric performance. Understanding and controlling the native defects in CuInTe2 provides a route toward n-type dopability as well as rational optimization of the p-type material.

Defect analysis and phase boundary mapping of Cu2HgGeTe4 and Hg2GeTe4 reveal reciprocal doping potential despite their similar crystal structures. Measurements validate predictions of Cu2HgGeTe4 as highly degenerate and Hg2GeTe4 as an intrinsic semiconductor.

eral applications such as a corrosion-and heat-resistant coating, [4,5] photo-and electrocatalyst, [6,7] as well as for thermal management [1] and extreme UV optics applications. [8] More recently, BP was identified as a potential p-type transparent conductive material (TCM). [9] This is a particularly interesting prospect, because obtaining high p-type conductivity in optically transparent materials is still an unsolved challenge. [10,11] Unlike the case of other p-type TCM candidates, bipolar doping has been reported in BP by various authors. [3,5,9,12,13] Thus, BP could be a unique example of a transparent material with both p-type and n-type doping capability. BP crystallizes in the diamond-derived zincblende structure with tetrahedral coordination. Because the electronegativity difference between B and P is small, BP is a covalent solid and its band structure is closely related to that of Si and C in the diamond structure. The main difference is an intermediate size of the fundamental indirect band gap for BP (≈2.0 eV) [14][15][16] mainly due to an intermediate bond length. Although this band gap corresponds to visible light, the direct band gap of BP is much wider and falls in the UV region (≈4.3 eV). [15][16][17] The weakness of indirect transitions predicted for BP at room temperature [15] is the key factor that could make BP thin films sufficiently transparent for many TCM applications. For example, a 100 nm-thick BP film is expected to absorb negligible amounts of red-yellow light and less than 10% of violet light according to first-principles calculations including electron-phonon coupling. [15] With respect to electrical properties, BP has a highly disperse valence band produced by p orbitals, ensuring low hole effective masses (0.35 m e ). [9] Unlike the case of diamond, the valence band maximum of BP lies at a relatively shallow energy with respect to the vacuum level. Shallow, disperse valence bands are usually correlated with high p-type dopability, due to easier formation of uncompensated shallow acceptor defects. [18,19] Open Questions in BP Research Conductivity and TransparencyThe highest conductivity reported for p-type BP is 3600 S cm −1 for a nominally undoped single-crystalline film deposited by chemical vapor deposition (CVD) at 1050 °C using B 2 H 6 and With an indirect band gap in the visible and a direct band gap at a much higher energy, boron phosphide (BP) holds promise as an unconventional p-type transparent conductor. This work reports on reactive sputtering of amorphous BP films, their partial crystallization in a P-containing annealing atmosphere, and extrinsic doping by C and Si. The highest hole concentration to date for p-type BP (5 × 10 20 cm −3 ) is achieved using C doping under B-rich conditions. Furthermore, bipolar doping is confirmed to be feasible in BP. An anneal temperature of at least 1000 °C is necessary for crystallization and dopant activation. Hole mobilities are low and indirect optical transitions are stronger than that predicted by theory. Low crystalline qua...

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Thermoelectric materials convert heat energy into electricity, hold promising capabilities for energy waste harvesting, and may be the future of sustainable energy utilization. In this work, we successfully synthesized core–shell Bi2Te3/Sb2Te3 (BTST) nanostructured heterojunctions via a two-step solution route. Samples with different Bi2Te3 core to Sb2Te3 shell ratios could be synthesized by controlling the reaction precursors. Scanning electron microscopy images show well-defined hexagonal nanoplates and the distinct interfaces between Bi2Te3 and Sb2Te3. The similarity of the area ratios with the precursor ratios indicates that the growth of the Sb2Te3 shell mostly took place on the lateral direction rather than the vertical. Transmission electron microscopy revealed the crystalline nature of the as-synthesized Bi2Te3 core and Sb2Te3 shell. Energy-dispersive X-ray spectroscopy verified the lateral growth of a Sb2Te3 shell on the Bi2Te3 core. Thermoelectric properties were measured on pellets obtained from powders via spark plasma sintering with two different directions, in-plane and out-of-plane, showing anisotropic properties due to the nanostructure alignment in the pellets. All samples showed a degenerate semiconducting character with the electrical resistivity increasing with the temperature. Starting from Sb2Te3, the electrical resistivity increases with the increase in amounts of Bi2Te3. Thermal conductivity is lowered due to the increase in interfaces and additional phonon scattering. We show that the out-of-plane direction of the BTST 1-3 sample (where 1-3 indicates the ratio of BT to ST) demonstrates a high Seebeck value of 145 μV/K at 500 K which may be attributed to an energy filtering effect across the heterojunction interfaces. The highest overall zT is observed for the BTST 1-3 sample in the out-of-plane direction at 500 K. The zT values increase continuously over the measured temperature range, indicating a probable higher value at increased temperatures.

Layered Zintl phases with A2MPn2 stoichiometry are an underexplored class of potential thermoelectric materials with complex and diverse chemistry. The solid solution Yb2–x Eu x CdSb2 is an example of the promise these compounds hold, as one composition, Yb1.64Eu0.36CdSb2, has reported one of the highest zTs of any Zintl phase material at 525 K. The present study examines changes in structure and bonding of this solid solution that impacts thermoelectric performance. Pair distribution function analysis is combined with electronic structure modeling to take a chemical bonding-based approach to deconvolute the impact of defects on thermal and electronic properties in Yb2–x Eu x CdSb2. Yb2–x Eu x CdSb2 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) samples were synthesized, and thermoelectric properties and defect chemistry were investigated. Samples from the middle of the series x = 0.2 and 0.3 were found to be the most highly defected, exhibiting Yb and Sb vacancies, as well as distortions in the Yb–Sb coordination spheres that correlate with thermoelectric properties. The highest efficiency is reported for x = 0.4 (zT ≈ 0.9 at 525 K), and the thermoelectric quality factor predicts that x = 0.3 could achieve zT > 2 by synthetically tuning the defect structure and thereby carrier concentration. The strategy of investigating local structure outlined in this study can be applied to a variety of other thermoelectric materials to provide insight into the hidden role of defect chemistry in understanding the structure–property relationships in extended solids.