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Characterization and photoluminescence properties of ultrafine copper molybdate(α-CuMoO_4) powders prepared via a combustion-like process

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International Journal of Minerals,Metallurgy and Materials 2016年第11期23卷 1340-1345页

作者： Mohamed Benchikhi Rachida El Ouatib sophie guillemet-fritsch Lahcen Er-Rakho Bernard Durand Laboratoire de Physico-Chimie des Matériaux Inorganiques Faculté des Sciences Ain Chock Université Hassan Ⅱ Casablanca Institut Carnot CIRIMAT CNRS Université de Toulouse

We report a simple method for preparing copper（II） molybdate（CuMoO_4） powders via a combustion-like process. A gel was first prepared by the polymerizable complex method, where citric acid was used as a complexing and polymerizing agent and nitric acid was used as an oxidizing agent. The thermal decomposition behavior of the（CuMo）-precursor gel was studied by thermogravimetry–differential thermal analysis（TG–DTA）, Fourier transform infrared spectroscopy（FTIR）, and X-ray diffraction（XRD）. We observed that the crystallization of CuMoO_4 powder was completed at 450°C. The obtained homogeneous powder was composed of grains with sizes in the range from 150 to 500 nm and exhibited a specific surface area of approximately 5 m^2/g. The average grain size increased with increasing annealing temperature. The as-prepared CuMoO_4 crystals showed a strong green photoluminescence emission at room temperature under excitation at 290 nm, which we mainly interpreted on the basis of the Jahn-Teller effect on [MoO_4^（2-）] complex anions. We also observed that the photoluminescence intensity increased with increasing crystallite size.

关键词： copper molybdate chemical synthesis photoluminescence Jahn-Teller effect

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Dielectric Properties of Colossal Permittivity Materials： An Update

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Journal of Energy and Power Engineering 2013年第4期7卷 726-732页

作者： Chafe Cheballah Zarel Valdez-Nava Lionel Laudebat Thierry Lebey Pierre Bidan Sombel Diaham sophie guillemet-fritsch LAPLACE (Laboratoire Plasma et Conversion d'Energie) Universite de Toulouse Toulouse 9 F-31062 France CNRS (Centre National de la Recherche Scientifique) LAPLACE Toulouse F-31062 France Centre Universitaire Jean-Frangois Champollion Albi 81012 France Institut Carnot CIRIMA T (Centre Inter-universitaire de Recherche et d 'lngdnierie des Matdriaux) Universitd Paul Sabatier Toulouse 9 31062 France

During the last 10 years, a lot of interests have been devoted to the so-called CDC （colossal dielectric constant） materials. The first materials exhibiting this behavior were the perovskite-based ceramics on the CCTO （CaCuaTi4012） composition. Relative dielectric permittivity can attain values up to （or even larger than） 105. Nevertheless, their dielectric losses are too high, the lower values ranging 10%, in a narrow frequency range, thus limiting their applications. The underlying physical mechanisms at the origin of the CDC are still under study. The analysis of broadband impedance spectroscopy measurements leads most of the authors to propose an interracial polarization mechanism （at the electrodes or at internal barriers）, there is a limited number of complementary electrical characterization techniques, which, up to now, comfort the proposed interracial polarization mechanisms. In the present work, I-V and time-domain polarization are used to characterize these materials. One of the main results is the observation of a non-symmetrical response of these materials related to the direction of the polarization. These results are observed for both macroscopic level on bulk polycrystalline material and within individual grains of the same samples. These results do not fit current accepted models for polarization for CDC materials.

关键词： Colossal permittivity CaCu3Ti4Oi2 CCTO dielectric properties.

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