Equivalent parameters for series thermoelectrics

We study the physical processes at work at the interface of two thermoelectric generators (TEGs) thermally and electrically connected in series. We show and explain how these processes impact on the system's performance: the derivation of the equivalent electrical series resistance yields a term whose physical meaning is thoroughly discussed. We demonstrate that this term must exist as a consequence of thermal continuity at the interface, since it is related to the variation of the junction temperature between the two TEGs associated in series as the electrical current varies. We then derive an expression for the equivalent series figure of merit. Finally we highlight the strong thermal/electrical symmetry between the parallel and series configurations and we compare our derivation with recent published results for the parallel configuration

Structure, electrical conductivity and electrochemical behavior of (La1-xSrx)2(Ni0.9Mn0.1)O4+δ based compounds

Solid oxide fuel cells typically operate at temperatures near 800 °C. One obstacle to reducing this temperature is finding a high-performance cathode for lower temperatures. La2NiO4+δ (LNO) has shown promise as a good material as a cathode being a well-known mixed electronic and ionic conductor. However, increasing the surface exchange in LNO is important for high performance applications. Mn substitution has been shown to increase the surface exchange of LNO with Sr required to stabilize the structure. Changing the ratio of Mn:Sr will change the oxidation state of Mn and Ni and the fundamental properties of the material. Changing the Sr content in (La1-xSrx)2(Ni0.9Mn0.1)O4+δ was investigated with x = 0.1-0.5. The XRD patterns shows a single phase K2NiF4 structures. Above 35% Sr the ‘a’ parameter of the unit cell starts increasing and the ‘c’ parameter starts to decrease. Increasing Sr content showed increased electrical conductivity from 40 S cm−1 to 261 S cm−1. Impedance data of the 10% Sr sample showed behavior similar to LNO sample with slightly increased area specific resistance (ASR); any further increase in Sr content further increases ASR of the electrode

Orienting MoS2_{2} flakes into ordered films

Layered transition metal di-chalcogenide (TMD) materials exhibit a unique combination of structural anisotropy combined with rich chemistry that confers controllability over physical properties such as bandgap and magnetism. Most research in this area is focused on single layers that are technologically challenging to produce, especially when trying to dope and alloy the host lattice. In this work, we use MoS2 flakes as a model system for the production of deliberately oriented films for practical applications in which anisotropic materials are required. The proposed production method combines ball milling with exfoliation in solution of MoS2 flakes, followed by their arrangement on a large centimeter-scale substrate by a simple and non-expensive procedure. The results show that the level of orientation achieved using the proposed system is as good as that of materials that were pressed and subjected to thermal treatment. The ball milling and exfoliation processes maintain the original crystalline structure of the MoS2 flakes, and the XRD results show that additional crystallographic phases were not produced. Lattice parameters are preserved, which verifies that other species such as water molecules did not intercalate into the MoS2 molecules. The proposed method of producing oriented films is universal, and as such, it is useful both for pure materials and for mixtures of compounds, the latter of which can be used to produce films with specifically tailored physical properties