Cobalt aluminate CoAl 2 O 4 powder, constituted of nano-sized crystallites, is prepared, involving the reactivity of AlCl 3 and CoCl 2 with molten alkali-metal nitrates. The reaction at 450 °C for 2 h leads to a mixture of spinel oxide Co 3 O 4 and amorphous γ-Al 2 O 3 . It is transformed into the spinel oxide CoAl 2 O 4 by heating at 1000 °C. The powders are mainly characterized by XRD, FTIR, ICP, electron microscopy and diffraction, X-EDS and diffuse reflection. Their properties are compared to those of powders obtained by solid state reactions of a mechanical mixture of chlorides or oxides submitted to the same thermal treatment.

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CaCu 3 Ti 4 O 12 (CCT) is a material of high interestsince colossal permittivity (ε>10 5 ) has been evidenced in these ceramics. Such properties make it a good candidate for capacitor applications. Electrical characterizations have been carried out on samples of CCT, namely impedance spectroscopy and conduction current measurements. A previous work concerning the modeling of this material showed good agreement with the measurements performed on samples at room temperature and in 10 2 -15.10 6 Hz frequency range [1]. In this paper, new results are presented. On one hand, different materials ranging from pure CCT to multiphase materials presenting different geometries have been manufactured [2][3]. On the other hand, further impedance spectroscopy measurements have been carried out thanks to a Novocontrol impedance spectroscopy set in a wide range of temperature and frequencies, respectively 120 to 470K and 10 -1 -10 7 Hz. Polarization current measurements thanks to a Keithley 6517A electrometer were directed in parallel. The preliminary study [1] in frequency domain from small signal measurements coupled with static conduction current measurements lead us to implement an electrical model well fitted for simulations in time domain. This frequency model is converted into a time domain model (state space representation) using the Diffusive Representation tool. In this paper, this approach is extended taking into account temperature influence.

This is an author's version published in: http://oatao.univ-toulouse.fr/23777 ARTICLE INFO ABSTR ACT Keywor ds:ZnO Spark plasma slntering Nanopartlcles CeramJcs MicrostructureDue to the sensitivity of nanopowders and the challenges in controlling the grain sire and the density during the sintering of ceramics, a systernatic study was proposed to evaluate the densifi cation and the microstructure of ZnO oeramics using sparlc plasma sintering technique. Cornrnercially available ZnO powder was dried and sin tered at various parameters (ternperature (400-900 °C), pressure (250--850 MPa), atmosphere (Air/Vacuum) etc.). High pressure sintering is desirable for rnaintaining the nanostructure, though it brings a difficulty in obtaining a fully dense ceramic. Whereas, increasing the ternperature from 600 to 900 •c results in fully den sifi ed ceramics of about 99% which shows tn have big impact on the grain size. However, a high relative density of 92% is obtained at a ternperature as low as 400 •c under a pressure of 850 MPa. The application of pressure during the holding tirne seems tn lower the grain sire as compared to ceramics pressed during initial stage (room ternperature).

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Submicronic CoAl 2 O 4 powders were prepared by double decomposition reaction between solid LiAlO 2 and molten KCoCl 3 at 500 • C for 24 h. The reaction mechanism involves the dissolution of LiAlO 2 shifted by the precipitation of CoAl 2 O 4 until complete transformation and the reaction leads to powders with a very homogeneous chemical composition. The powders obtained were mainly characterized by XRD, FTIR, ICP, X.EDS, electron microscopy and diffraction and diffuse reflexion. The blue pigments obtained exhibit a high thermic stability allowing their use for the colouring of ceramic tiles.

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Rhombohedral LaMnO 3+δ powders, prepared by two different soft chemistry routes (co-precipitation and hydrothermal synthesis), are sintered at 1400 • C for 2 h in air. Measurements of internal friction Q −1 (T) and shear modulus G(T), at low frequencies from −180 to 700 • C under vacuum, evidence three structural transitions of nearly stoichiometric orthorhombic LaMnO 3+δ . The first one, at 250 or 290 • C, depending on the processing followed, is associated to either a Jahn-Teller structural transition or a phase transformation from orthorhombic to pseudo-cubic. The second one at 610 or 630 • C is related to a phase transformation from pseudo-cubic or orthorhombic to rhombohedral. Below the Neel temperature, around −170 • C, a relaxation peak could be associated, for samples prepared according to both processing routes, to the motion of Weiss domains.