Research Project: Yüksek Verimli N- Ve P-Tipi Termoelektrik Malzemelerin Ve Modüllerin Üretimi
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Contributors
Funders
ID
TB.00421
Authors
Aydemir, Umut
Faculty Member
Publications
Enhanced thermoelectric performance and low thermal conductivity in Cu2GeTe3 with identified localized symmetry breakdown
(American Chemical Society, 2023) Aydemir, Umut; Qin, Feiyu; Hu, Lei; Zhu, Yingcai; Li, Yushan; Wang, Haitao; Wu, Haijun; Peng, Jun; Shi, Wen; Ding, Xiangdong; Department of Chemistry; KUBAM (Koç University Boron and Advanced Materials Application and Research Center); Yes; College of Sciences; Research Center
Highly efficient and eco-friendly thermoelectric generators rely on low-cost and nontoxic semiconductors with high symmetry and ultralow lattice thermal conductivity kappa L. We report the rational synthesis of the novel cubic (Ag, Se)-doped Cu2GeTe3 semiconductors. A localized symmetry breakdown (LSB) was found in the composition of Cu1.9Ag0.1GeTe1.5Se1.5 (i.e., CAGTS15) with an ultralow kappa L of 0.37 W/mK at 723 K, the lowest value outperforming all Cu2GeCh3 (Ch = S, Se, and Te). A joint investigation of synchrotron X-ray techniques identifies the LSB embedded into the cubic CAGTS15 host matrix. This LSB is an angstrom ngstro''m-scale orthorhombic symmetry unit, characteristic of multiple bond lengths, large anisotropic atomic displacements, and distinct local chemical coordination of anions. Computational results highlight that such an unusual orthorhombic symmetry demonstrates low-frequency phonon modes, which become softer and more predominant with increasing temperatures. This unconventional LSB promotes bond complexity and phonon scattering, highly beneficial for extraordinarily low lattice thermal conductivity.
Enhancing thermoelectric and mechanical properties of P-Type (Bi, Sb)2Te3 through rickardite mineral (Cu2.9Te2) incorporation
(Amer Chemical Soc, 2023) Aydemir, Umut; Sağlık, Kıvanç; Yahyaoğlu, Müjde; Department of Chemistry; Graduate School of Sciences and Engineering; Yes; College of Sciences; GRADUATE SCHOOL OF SCIENCES AND ENGINEERING
Bi2Te3-based alloys are widely utilized in Peltier coolers owing to their highest thermoelectric performance at near-room-temperatures. However, their peak dimensionless thermo-electric figure of merit, zT, is limited to a narrow temperature window due to minority carrier excitation emerging upon heating at around 400 K. Here, we show how this issue can be overcome by incorporating a synthetic rickardite mineral, Cu3-xTe2, in p-type (Bi, Sb)2Te3. The significant enhancement of the electronic and thermal properties could be achieved due to small Cu incorporation into the crystal structure of (Bi, Sb)2Te3 and homogeneous precipitation of Cu3-xTe2 at the grain boundaries. This leads to a high average zT value (zTave) of 1.22 between 350 and 500 K for two compositions, Bi0.5Sb1.5Te3 (BST-5) and Bi0.3Sb1.7Te3 (BST-3), with peak zT values of 1.32 at 467 K and 1.30 at 400 K, respectively. These high zT values result in a considerably high maximum device ZT of ca. 1.15 and a theoretical efficiency of up to 7% between 325 and 525 K. Additionally, room-temperature micro-hardness is substantially improved, which is desirable for constructing reliable and durable thermoelectric modules.
