Rhodium-based Oxide Thermoelectric Materials Structure And Performance Studies

The core issue of thermoelectric materials is to improve the energy conversion efficiency, and looking for a kind of better thermoelectric material which work at room temperature and the geothermal temperature zone. Lots of new technology advancements in the field are dependent on the development and application of new thermoelectric materials, such as micro-electronic devices power generation, aerospace power supply, super-conducting refrigeration and so on. Thus exploring the transition metal oxide thermoelectric materials is one of the recent research focus. This article made a more detailed overview of the thermoelectric effect, thermoelectric parameters of the theory and research progress. Selecting rhodium oxide system La-Rh-O, Cu-Rh-O series and their Rh-site doping analysis as the research object, using a combination of theoretical calculations and experimental means to commence the study, explaining the conduction characteristics of the reasons for their good thermoelectric properties by using quantum chemical calculations methods. This article focus on calculating the doping of the La-Rh-O system and predicting the effect of thermoelectric properties due to different doping elements.The electronic structures of La-Rh-O and Cu-Rh-O system thermoelectric materials matrix and a variety of doped model are studied by CASTEP based on density functional theory and pseudopotential theory of quantum chemistry package, combined with the semi-classical Boltzmann transport theory, calculated by GGA which can calculate more accurate bond lengths and angles. Effective masses at the top of valence band and at the bottom of conduction band were deduced from band structure. According to these results, effective masses, carrier concentration, Fermi level, band gap width, the electronic conductivity, thermal conductivity, Seebeck coefficient of LaRhO3model at the room temperature were computed. The results were consistent with experimental measurements. Then, the thermoelectric parameters at different temperatures were predicted. The band structure reveals the form of impurity levels due to the substitutional impurity in semiconductor matrix, the conductivity is higher than that of the non-doped model. LaRhO3shows the character of p-type semiconductor, and intrinsic conductivity. According to experiment measurements, LaRhO3can be used as the matrix material for which have better thermoelectric properties and by doping can improve the thermoelectric properties. Through theoretical analysis and experimental verification, found La2CuRhO6is one of the best thermoelectric materials, La2CoRhO6, La2NiRhO6, La2CrRhO6was followed in turn.The Cu-Rh-O system three structures and doped models were calculated by first principles. Similar cobaltite mismatch layer structure was found from the model. The contribution of Cu, Rh and O atoms to the valence band and conduction band near Fermi level is larger, the contribution of Cu atom is largest, the contribution of Mg atom is almost zero. It is found that Rh-O and Cu play a decisive role on the the conductive properties of materials through the density of states, theory testing the reason that conductivity of the Cu layer and RhO2layer were similar at room temperature300K, and found that the metal transition only exists in the plane of Rh-O-Rh and Cu layer by doping. Therefore, it is found high conductivity parallel to the plane direction, low conductivity perpendicular to the layer direction.In the three structural models, the Fermi level gradually increased by doping Mg, showing Mg is the donor level. CuRhO2is p-type semiconductor, with the increase of doping Mg, the macroscopic properties of the material began to change into the n-type semiconductor, accompanied by a band gap narrowing and the conductivity increased. Cu24Mg2Rh22O48, Cu24Mg6Rh18O48, Cu24Mg9Rh15O48showing typical metal electronic properties, high conductivity, low resistivity. In the other two structures, it is found metal-semiconductor-metal transition with the increase of doping Mg.32, Cu8Rh8Co8O32show higher conductivity.