Generalized theory of the self-induced voltage by seebeck effect in frequency domain

Abstract

In previous studies, photothermoelectric (PTE) technique was introduced in photothermal sciences for the thermal characterization of solid-state thermoelectric materials. In this work, we demonstrate that the shape of the PTE signal is directly impacted by the electrical conductivity of the medium. Here, a generalized formulation of the PTE signal is established from the framework of the Onsager theory. This is achieved by taking into account the coupling effects between thermal and electrical field when a thermoelectric material is submitted to a modulated Gaussian light beam. Three materials were investigated at ambient temperature: Titanium trisuflide (TiS3), Bi2Ca2Co1.7Ox and Bismuth Selenido-telluride (Bi2Te2.4Se0.6). This last one exhibits a high efficiency at ambient temperature due to an advantageous electrical conductivity. Although signals of these two first samples can be analyzed with a classical PTE model assuming a 1D heat propagation, Seebeck voltage generated by a Bi2Te2.4Se0.6 sample must be processed with a generalized expression of the PTE signal to get a reliable result. PTE normalized signals obtained for Bi2Ca2Co1.7Ox and Bi2Te2.4Se0.6 samples are displayed respectively in Fig. 1-a) and Fig. 1-b). Thermal parameters values obtained from the extended signal expression were compared with those obtained with photothermal radiometry, showing a good accordance and demonstrating the relevance of this new approach.