Germanium telluride is a high performing thermoelectric material that additionally serves as a base for alloys such as GeTe–AgSbTe 2 and GeTe–PbTe. Such performance motivates exploration of other GeTe alloys in order understand the impact of site substitution on electron and phonon transport. In this work, we consider the root causes of the high thermoelectric performance material Ge 1− x Mn x Te. Along this alloy line, the crystal structure, electronic band structure, and electron and phonon scattering all depend heavily on the Mn content. Structural analysis of special quasirandom alloy structures indicate the thermodynamic stability of the rock salt phase over the rhombohedral phase with increased Mn incorporation. Effective band structure calculations indicate band convergence, the emergence of new valence band maxima, and strong smearing at the band edge with increased Mn content in both phases. High temperature measurements on bulk polycrystalline samples show a reduction in hole mobility and a dramatic increase in effective mass with respect to increasing Mn content. In contrast, synthesis as a function of tellurium chemical potential does not significantly impact electronic properties. Thermal conductivity shows a minimum near the rhombohedral to cubic phase transition, while the Mn Ge point defect scattering is weak as indicated by the low K L dependence on the Ge–Mn fraction (Fig. 10). From this work, alloys near this phase transition show optimal performance due to low thermal conductivity, moderate effective mass, and low scattering rates compared to Mn-rich compositions.
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Synthesis, transport properties and electronic structure of p-type Cu 1+x Mn 2−x InTe 4 ( x = 0, 0.2, 0.3)
The synthesis, electronic structure and temperature dependent transport properties of polycrystalline Cu 1+x Mn 2−x InTe 4 ( x = 0, 0.2, 0.3) are reported for the first time. These quaternary chalcogenides were synthesized by direct reaction of the elements, followed by solid state annealing and hot press densification. The thermal conductivity is low for all specimens and intrinsic to the material system. Furthermore, the off-stoichiometry specimens illustrate the sensitivity of the transport properties to stoichiometry, with a greater than two-orders-of magnitude increase in carrier concentration with increased Cu content. First principles calculations of the electronic structure are also reported, and are in agreement with the experimental data. This fundamental investigation shows the potential towards further optimization of the electrical properties that, in addition to the intrinsically low thermal conductivity, provides a basis for further research into the viability of this material system for potential energy-related applications.
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- Award ID(s):
- 1748188
- PAR ID:
- 10142926
- Date Published:
- Journal Name:
- Dalton Transactions
- Volume:
- 49
- Issue:
- 7
- ISSN:
- 1477-9226
- Page Range / eLocation ID:
- 2273 to 2279
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Temperature‐dependent thermal properties of phase‐pure polycrystalline ternary chalcogenides Cu4Bi4S9and Cu4Bi4Se9are reported. The structure and bonding in these materials result in very low thermal conductivity values (<0.8 W m−1 K−1at room temperature) for both materials. The lattice contribution, Debye temperatures, and Sommerfeld coefficient are obtained from low‐temperature heat capacity data that also indicate very small electronic contributions to the heat capacity for these materials. This study aids in the identification of new nontoxic, earth‐abundant resistive ternary chalcogenide materials with low thermal conductivity for potential thermal barrier coating and rewriteable storage applications.
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/c9dt04069b
