Title : Ceramics thermoelectrics materials for "green" power generation
October 2010 to September 2013, defended the 26th September 2013.
3-year scholarship by the Ministère de la Recherche et de l'Enseignement Supérieur at Université Paris Sud
Winner of the price Bernard Coqblin in 2014 from the french GDR of thermoelectricity
Commitee :
Mme Pascale Foury, Université Paris Sud (Orsay) - Présidente
Mme Anne Dauscher, Université de Lorraine (Nancy) - Rapporteur
M. Gérard Aka, Ecole Nationale Supérieure de Chimie de Paris (Paris) - Rapporteur
M. Michaël Pollet, Université de Bordeaux (Bordeaux) - Examinateur
M. David Bérardan, Université Paris Sud (Orsay) - Examinateur
M. Nita Dragoe, Université Paris Sud (Orsay) - Directeur de Thèse
Abstract :
This thesis addresses the issues of the elaboration and the characterization of the chemical and physical properties of a new family of thermoelectric materials, the oxychalcogenides with the general formula BiCuSeO. This compound, called 1111, cristallises in the ZrCuSiAs structure-type. One feature of this structure lies in the fact that the layers are considered as electronically distinct: the Bi2O2 layers are described as the insulating layers whereas the chalcogenide layers Cu2Se2 are presented as the conductive ones. The study of BiCuSeO exhibits that in spite of a relatively moderate power factor (S²σ), this compound is very promising as possible thermoelectric material, especially at high temperature. Indeed, BiCuSeO shows a remarkably low thermal conductivity, which can achieve relatively high figures of merit. In addition, BiCuSeO offers many ways for improvement. One of them concerns the study of aliovalent doping on the bismuth site. The results showed that the insertion of a divalent element optimizes the charge carriers concentration, leading to a sharp increase in the figure of merit of the compound. Another possible way of exploration lies the study of the influence of the chalcogen ion, notably through the substitution of selenium and tellurium, with acomplete solid-solution BiCuSe1-xTexO. The study of the electrical properties of this solid solution has highlighted the presence of a metal - semiconductor - metal transition for tellurium fractions below 0.5. Thus, although the influence of tellurium on the power factor is relatively limited due to this anomaly, interesting results were obtained for the high tellurium fractions. In addition, issues around an alternative method of synthesis of the material and its stability in air are also discussed in this work.