the-frequency-domain-thermoreflectance-technique-for-thermal-property

The Frequency Domain Thermoreflectance Technique for Thermal Property Measurements

The frequency domain thermoreflectance (FDTR) technique is a nondestructive method for thermal characterization and imaging with microscale spatial ...

Michigan State University

AMX compounds with the ZrBeSi structure tolerate a vacancy concentration of up to 50 % on the M-site in the planar MX-layers. Here, we investigate the impact of vacancies on the thermal and electronic properties across the full EuCu Zn Sb solid solution. The transition from a fully-occupied honeycomb layer (EuCuSb) to one with a quarter of the atoms missing (EuZn Sb) leads to non-linear bond expansion in the honeycomb layer, increasing atomic displacement parameters on the M and Sb-sites, and significant lattice softening. This, combined with a rapid increase in point defect scattering, causes the lattice thermal conductivity to decrease from 3 to 0.5 W mK at 300 K. The effect of vacancies on the electronic properties is more nuanced; we see a small increase in effective mass, large increase in band gap, and decrease in carrier concentration. Ultimately, the maximum zT increases from 0.09 to 0.7 as we go from EuCuSb to EuZn Sb.

Investigating the Role of Vacancies on the Thermoelectric Properties of EuCuSb-Eu ZnSb Alloys.

AMX Zintl compounds, crystallizing in several closely related layered structures, have recently garnered attention due to their exciting thermoelectric properties. In this study, we show that orthorhombic CaAgSb can be alloyed with hexagonal CaAgBi to achieve a solid solution with a structural transformation at  ∼ 0.8. This transition can be seen as a switch from three-dimensional (3D) to two-dimensional (2D) covalent bonding in which the interlayer M-X bond distances expand while the in-plane M-X distances contract. Measurements of the elastic moduli reveal that CaAgSbBi becomes softer with increasing Bi content, with the exception of a steplike 10% stiffening observed at the 3D-to-2D phase transition. Thermoelectric transport measurements reveal promising Hall mobility and a peak  of 0.47 at 620 K for intrinsic CaAgSb, which is higher than those in previous reports for unmodified CaAgSb. However, alloying with Bi was found to increase the hole concentration beyond the optimal value, effectively lowering the . Interestingly, analysis of the thermal conductivity and electrical conductivity suggests that the Bi-rich alloys are low Lorenz-number () materials, with estimated values of  well below the nondegenerate limit of  = 1.5 × 10 W Ω K, in spite of the metallic-like transport properties. A low Lorenz number decouples lattice and electronic thermal conductivities, providing greater flexibility for enhancing thermoelectric properties.

Article	Year
Investigating the Role of Vacancies on the Thermoelectric Properties of EuCuSb-Eu ZnSb Alloys. Angewandte Chemie (International ed. in English)\| PubMed ID: 37143187	2023
Alloying-Induced Structural Transition in the Promising Thermoelectric Compound CaAgSb. Chemistry of materials : a publication of the American Chemical Society\| PubMed ID: 38533450	2024

Sevan Chanakian

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