Resultant Seebeck coefficient formulated by combining the Thomson effect with the intrinsic Seebeck coefficient of a thermoelectric element

摘要

The resultant Seebeck coefficient α_R(T_z) of a thermoelectric (TE) element was derived analytically from the temperature dependence of the intrinsic Seebeck coefficient α_1(T_z) by taking into account the Thomson effect, where T_z is a temperature at z along a TE element. The analysis was performed by expanding α_1(T_z) in a power series in (T_z - T), where T is a mean temperature. As a result, when α_1(T_z) has a convex curve exhibiting a local maximum at T_z - T, α_R(T_z) is increased at the interfaces of a TE element, while when it has a concave curve giving a local minimum at T_z = T, α_R(T_z) deteriorates there. If the p-type (Bi_(0.4)Sb_(0.6))_2Te_3 with a local maximum of α_1(T_z) at T= 390 K is employed for a TE element, α_R(T_z)/α_1(T) at both interfaces is increased up to 1.53 under the condition of T=390K and AT=200K. A similar enhancement in α_R(T_z)/α_1(T) appeared even in the n-type (Zr-Hf)NiSn half-Heusler. When α_1(T_z) varies nonlinearly with changes in T_z, therefore, the TE figure of merit Z_R(T_z)T_z is found to be affected dramatically at the interfaces. The average resultants Z_(AR)(T) estimated for the p-type Bi-Te and n-type half-Heusler compound reach great values of 1.46 and 1.26 times as large as their intrinsic Z(T), respectively. The experimental method to confirm such a phenomenon is also proposed here. The performance of a TE element is thus expected to be enhanced significantly not only by improving the intrinsic Z(T_z)T_z but also by optimizing the T_z-dependence of α_1(T_z).