Ce travail a pour corpus central les œuvres musicales de trois compositeurs contemporains d’origine arabe : Ahmed Essyad, Zad Moultaka et Saed Haddad. Les démarches compositionnelles de ceux-ci ont en commun qu’elles s’inscrivent dans la pensée critique propre à la modernité musicale occidentale, tout en réinvestissant certains matériaux et procédés dérivés de musiques traditionnelles orales du monde arabe. Aussi le matériau emprunté à la musique orale se trouve à la fois déployé et néanmoins contrarié dans ce qu’il pouvait induire comme conduite normative. Dès lors, l’élément musical de la culture d’origine advient en se transformant, et laisse émerger ce faisant de nouvelles potentialités, quitte à devenir alors non-immédiatement perceptible.En analysant les différents processus d’un tel devenir, ce travail interroge la notion de tradition musicale et, à travers elle, la catégorie de l’identité. Les grands bouleversements socioculturels observés depuis l’époque industrielle ont si profondément atteint les pratiques musicales orales que de telles catégories – tradition et identité – ne peuvent plus se présenter que comme problématiques. Ce travail entend rendre compte du fait que le rapport au patrimoine musical peut s’avérer être d’autant plus vif et fructueux dès lors qu’il s’affranchit de l’impératif identitaire. Dans cette perspective, la contemporanéité est envisagée comme distance critique essentielle par rapport à ce qui se présente comme immédiatement donné, y compris son propre acquis culturel ; son champ opératoire devient a fortiori la relation. Ces réflexions sont, du reste, inspirées d’auteurs comme Theodor Adorno, Walter Benjamin et Édouard Glissant. / The central corpus of this work consists of three contemporary composers of Arab origin: Ahmed Essyad, Zad Moultaka et Saed Haddad.Their compositional approaches have a shared basis in the critical thought of western musical modernity, while at the same time they reinvest certain materials and processes derived from traditional oral music of the Arab-Berber world. In addition, the material borrowed from oral music is both deployed and yet thwarted in what it could induce as normative conduct. Consequently, the musical element of the culture of origin occurs by transforming itself, and lets emerge new potentialities, which may not be immediately perceptible.Analyzing the different processes of such a development, this work interrogates the notion of traditional music as well as the category of identity contained within. The major socio-cultural upheavals witnessed since the industrial period have so profoundly affected these oral musical practices that such categories – tradition and identity – must be viewed as problematic. This work intends to account for the fact that the relation to musical heritage can prove to be all the more lively and fruitful as soon as it breaks with the imperative of identity. From this perspective, contemporaneity is envisaged as a critically essential distance in relation to that which presents itself as immediately given, including its own cultural heritage. Its operative field becomes the a fortiori relation. These reflections are influenced by the work of thinkers such as Theodor Adorno, Walter Benjamin and Édouard Glissant.

This PhD thesis presents investigations of perovskite-related compounds in systems of interest for applications in components in solid oxide fuel cells. The compound compositions derive from substitutions in the parent compounds LaCoO3, LaCrO3 and SrFeO3. Novel phases La2Co1+z(MgxTi1-x)1-zO6 were synthesized and investigated with regard to structure, thermal expansion, electronic and magnetic properties. The study focused on the composition lines La2Co(MgxTi1-x)O6 (z=0), where the oxidation state of Co nominally changes from +2 (x=0.0) to +3 (x=0.5), and La2Co1+z(Mg0.5Ti0.5)1-zO6, with a varying fraction of Co3+ ions. XANES data show that the Co ions in the system have discrete oxidation states of +2 and +3. The TEC increases with increasing x due to an increasing contribution from spin state transitions of the Co3+ ions. Novel compounds La2Cr(M2/3Nb1/3)O6 with M=Mg, Ni, Cu were synthesized and characterized with respect to structure and magnetic properties. XRPD and NPD data indicate Pbnm symmetry; however, SAED patterns and HREM images indicate a P21/n symmetry for M=Mg, and Cu. The magnetic measurements results were rationalized using the Goodenough-Kanamori rules. Oxygen-deficient phases with x≥0.63 in SrxY1-xFeO3-δ and Sr0.75Y0.25Fe1-yMyO3-δ (M=Cr, Mn, Ni and y=0.2, 0.33, 0.5), were synthesized and characterized with respect to structure, oxygen content, thermogravimetry, TEC, conductivity and magnetic properties. Powder patterns of phases agree with cubic  perovskite structures. NPD data for x=0.75 reveal anisotropic displacement for the O atom, related to local effects from Fe3+/Fe4+ ions. SAED patterns for x=0.75 reveal the presence of an incommensurate modulation. The compounds start to lose oxygen in air at ~ 400°C. The TEC up to ~400°C for x=0.75 is ~10.5 ppm/K and increase to ~17.5 ppm/K at higher temperatures. The conductivity for x=0.91 is 164 S/cm at 400°C. Partial substitution of Fe by Cr, Mn or Ni does not increase the conductivity or decrease TEC.

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The well-known lanthanide cuprates exist in two principal forms, T and T´, which behave as p-type and n-type conductors, respectively. In order to understand the structural properties and crystal chemistry from the T to T´ phase, the Nd₁.₈₋ₓLaₓPr₀.₂CuO₄ (NLPCO) system was studied varying the La substitution ratio (0≤x≤1.8) and then characterised using high temperature X-ray powder diffraction. From analysis of the X-ray diffraction patterns obtained at room temperature, there are clearly five distinguishable regions for the NLPCO system. They are, (1) monophasic T´ solid–solution (2) two phase mixture T´ + T´´ (3) monophasic T´´solid–solution (4) two phase mixture T´´ + O and finally (5) monophasic O phase solid–solution. The T´´ form has previously been suggested as an ordered form of T´; however here we show via high temperature X-ray diffraction studies that it is a non-transformable metastable phase formed on quenching of the T phase via an orthorhombically distorted variant. Also neutron diffraction and selected area electron diffraction (SAED) studies confirmed that the T ´´phase is 4- fold Cu coordinated. The structural, magnetic and electrical properties of this NLPCO series have been investigated for the selected compositions using X-ray diffraction, magnetization measurements, thermal analysis and conductivity measurements. The aim of the second half of this work was to discover the basic high temperature electrical characteristics of Nd₂₋ₓPrₓCuO₄ and investigate how this matches with those required for components on the SOFC cathode side to identify which dopant level shows highest conductivity and whether it is stable at different temperatures. The idea was to make a new concept in SOFC cathodes and current collector development, using n-type conductors instead of p- type conductors and to try to produce a high conductivity material which is stable under the chemical and thermal stresses that exist while under load that can be used in cathode or current collector applications. The Nd₂₋ₓPrₓCuO₄ (NPCO) series has been studied over a range of dopant levels (x=0.15 - 0.25) and maximum conductivity of 86.7 Scm⁻¹ has been obtained for the composition where x = 0.25. Also NPCO shows n-type semiconductor behaviour which gives operational advantages when operating at mild oxygen deficiency. AC impedance studies have been carried out on symmetrical cells to investigate the performance of NPCO as a cathode material. These studies mainly focused on polarization resistance and the activation energies of the cells. Low Rp values and low activation energies are obtained for a composite cathode compared to pure cathode material. Two configurations of NPCO as cathode materials were tested, pre-fired and in-siu fired. Pre-fired NPCO exhibited better performance than in-situ fired NPCO. Both in-situ and pre-fired current collecting NPCO still showed lowest activation energies which suggest good catalytic activity. From all of these studies, it is evident that the praseodymium doped neodymium cuprate material shows considerable promise as a potential cathode material for solid oxide fuel cell applications.