Articles you may be interested inEffect of electron doping on thermoelectric properties for narrow-bandgap intermetallic compound RuGa2Transport properties of polycrystalline TMGa 3 (TM= Fe, Ru, and Os) compounds are reported in the temperature range 313 K Ͻ T Ͻ 973 K. These compounds exhibit semiconductorlike behavior with relatively high Seebeck coefficient and electrical resistivity. Hall carrier concentrations at room temperature are reported in the range of 10 17 -10 18 cm −3 . Seebeck coefficient measurements indicate that FeGa 3 and OsGa 3 are n-type material at the operating temperature; on the other hand, the Seebeck coefficient of RuGa 3 changes its sign rapidly from large positive value to large negative value around 450 K. The thermal conductivity of these compounds is estimated to be 3.5 W / mK at room temperature and decreases with increasing temperature. The absolute value of the lattice thermal conductivity for FeGa 3 , RuGa 3 , and OsGa 3 is 3.5 W / mK at room temperature, and decreases down to 2 W / mK at high temperature. The resulting thermoelectric figure of merit ZT at 945 K for RuGa 3 reaches 0.18.

We have measured the low-frequency characteristics of thermal voltage converters down to 1 Hz using a differential sampling measurement system based on ac-programmable Josephson voltage standard (AC-PJVS) system. The measured ac-dc transfer difference of a planar multijunction thermal converter using our system is evaluated to be < 1 μV/V above 10 Hz and < 35μV/V at 1 Hz with lower uncertainties compared to the conventional method. The estimated overall uncertainty measured by using our system is 3.1 μV/V (k = 1) at the frequency of 10 Hz and root-mean-square voltage of 3 V. Our measurement results above 10 Hz are in good agreement with the results obtained by the conventional method within a standard deviation of the mean. Our differential sampling measurement system using AC-PJVS is a useful tool for low-frequency ac voltage metrology.

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Stretchable thermoelectric generators (S-TEGs) have the potential to utilize waste heat from sources with complex and dynamic surfaces. However, their thermoelectric performances are still lower than those of conventional hard and rigid TEGs and are easily degraded by large or cyclic deformations due to electrical failure. An approach that improves both stretchability and thermoelectric performance is required. This study presents and explores the improvements enabled by an ultrasoft silicone sponge encapsulation for S-TEGs using silicone-encapsulated serpentine interconnects for the internal electrical wiring of the bismuth-telluride-based thermoelectric elements. The ultrasoft silicone sponge is characterized by a low Young’s modulus (0.01 MPa) and low thermal conductivity (0.08 W m−1 K−1) owing to its open-cell structure. We consider that the low Young’s modulus decreases the internal stress in the interconnects under deformation and that the low thermal conductivity increases the temperature differences in the thermoelectric elements under constant heat flow conditions. We fabricated S-TEGs with three different silicone encapsulations: hard and soft silicones, as used in previous studies, and an ultrasoft silicone sponge. We experimentally measured the elongation and cycle number to failure for stretchability evaluation as well as the open-circuit voltage and maximum power for thermoelectric performance evaluation. Thus, the S-TEG with the ultrasoft silicone sponge encapsulation showed both the highest stretchability (125% elongation to failure) and thermoelectric performance (1.80 μW cm−2 maximum power per unit area on a heater at 100 °C under natural air convection). Additionally, the S-TEG showed 153 μW cm−2 power per unit area on a heater at 100 °C under water cooling, and we confirmed its superior overall performance via comparisons with existing S-TEGs.

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