Effect of Silicon Substitution on Thermoelectric Properties of Heusler-type Fe<SUB>2</SUB>VAl Alloy

Abstract

We report on the temperature dependence of electrical resistivity, Seebeck coefficient and Hall coefficient of the Fe 2 VAl 1-y Si y alloys with Si compositions y＝0 0.20. While the Heusler type Fe 2 VAl ( y＝0) exhibits a semiconductor like resistivity behavior, a slight substitution of Si for Al causes a sharp decrease in the low temperature resistivity and a large enhancement in the Seebeck coefficient. Substantial enhancements for the Seebeck coefficient are in reasonable accord with changes in the Hall coefficient and can be explained on the basis of the electronic structure, where the Fermi level shifts slightly from the center of the pseudogap due to the substitution of Si. In particular, the Si substitution of y＝0.10 leads to a large power factor of 5.4×10 -3 W/m K 2 at room temperature, which is comparable to that of conventional thermoelectric materials.

Thermoelectric Properties of Fe₂VAl-Based Thin-Films Deposited at High Temperature

“…All samples indicated n-type behavior as we expected from the data reported for bulk samples of the same composition. Notably, maximum magnitude of Seebeck coef cient reached −120 μV K −1 at 340 K for the sample deposited at 1073 K. The temperature dependence and the magnitude of Seebeck coef cient were similar to the previously reported data of bulk sample obtained at Fe 2 VAl 0.95 Si 0.05 4,5) . In contrast, the thin-lms deposited at low temperatures below 973 K possessed smaller magnitude of Seebeck coef cient than bulk material.…”

“…The electrical resistivity moderately decreased with increasing temperature regardless of the sample preparation condition. The same behavior was observed even for the bulk samples at high temperatures above 400 K 5) . It is naturally attributed to the synergy effect of (1) the temperature independent mean free path of electrons in association with the strongest scattering limit known as Mott-Ioffe-Regel limit 14,15) , (2) the ne electronic structure (pseudogap) near the chemical potential, and (3) the gradually increasing energy-range where the electrons contribute to the electron transport properties with increasing temperature.…”

“…We selected Fe 2 VAl 0.95 Si 0.05 as the composition of target because a high power factor with n-type behavior was reported for the bulk samples at this composition [2][3][4][5] . Despite that the composition of lms form the Fe 2 VAl 0.95 Si 0.05 target had an excess of Fe due to the difference of sputtering probability, we controlled the composition by using an Al-V alloy chip placed at the center of target disk.…”

“…L2 1 -type Heusler phase stabilizes at around Fe 2 VAl is widely considered as one of the potential thermoelectric materials working at low temperature below 500 K. Its power factor reaches 5.5 mW m −1 K −2 at the optimal carrier concentration [2][3][4][5] . Notably this value is larger than that of Bi 2 Te 3 -based thermoelectric materials 1) .…”

Thermoelectric Properties of Amorphous Ge/Au and Si/Au Thin Films

“…It is well known that even pure Si and Ge form amorphous phase and show Mott transition whose band structure is called pseudogap when the metal element is added. There are many reports that the pseudogap system is expected to have a large enhancement in the thermoelectric power because the density of state nearby Fermi level causes a sharp decrease (14) (15) .…”