Speaker
Description
Thermoelectric materials are important for power-generation devices that can convert waste heat into electrical energy. This conversion may have an important role in the current challenge for the development of alternative energy technologies.
In the present work, the intermetallic thermoelectric materials with the formula RCu9Sn4 (R=Nd, Pr, La, Y) and their stoichiometric variations RCu9.4Sn3.6 have been first prepared and studied. The initial purpose of the work was to obtain tetra-cage materials in which the phenomena of rattling (oscillation of the central atom) is observed. This is expected to decrease the thermal conductivity, therefore increasing the final thermoelectric efficiency of the material. The materials were synthesized by arc melting and subsequently annealed. The heat treatments were carried out using the following sequential procedures: the annealing first lasted 21 days at 680 °C, followed 10 days at 800 °C. X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) were combined to characterize them. The analysis indicated that it was not possible to obtain monophasic samples before or after the thermal treatments. However, the treatments led to the formation of a novel phase for the Y and Nd samples, in course of characterization. An interesting point is that the secondary phase Cu3Sn was observed in all samples, in some with a significant percentage. The thermoelectric properties (electrical resistivity and Seebeck coefficient) were subsequently studied, but the results showed a low Seebeck coefficient for these materials.
Subsequently, the CeMSn (M = Cu, Ni) materials were prepared and studied. The work shifted to this family of compounds because they possess a high peak near the Fermi level in their Density of State (DOS). This is very interesting because the point at which the Fermi level intersects the DOS is related to the value of the Seebeck coefficient. In particular, the greater the slope at the point of intersection, the greater can be the value of the Seebeck coefficient. For this reason, samples have been synthesized by slightly varying the stoichiometry, Ce:M:Sn, to 1-0.9-1.1 and 1-1.1-0.9, to change the Fermi level. These samples were also synthesized by arc melting and annealing (10 days at 800 °C). Characterization with XRD and SEM proved some of them to be monophasic, a fundamental feature for a proper study of physical properties. Further studies will assess thermoelectric properties.
