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Relationships between crystalline structure and dielectric properties in Sr 2 Sm (1-x) Nd x Ti 2 Nb 3 O 15 ceramics

Abstract : In this study, tungsten-bronze type materials of Sr 2 Sm (1-x) Nd x Ti 2 Nb 3 O 15 composition (x=0; 0,25; 0,5; 0,75 and 1) were elaborated by classical solid-state reaction. The structural characterization demonstrate that these compounds present tetragonal symmetry, using two space groups P4bm (N°100) and P4/mbm (N°127) respectively. The lattice parameters are a=b≈12,2Ǻ; c≈3,8Ǻ; V≈579,0 3 Ǻ and Z=2. In this compounds, Ti and Nb cations show obvious off-center displacements along the c axis in both the Ti/Nb(1)O 6 and the Ti/Nb(2)O 6 octahedra. Besides, the unequal Ti/Nb(2)-O bonds length in the equatorial plane of Ti/Nb(2)O 6 octahedra indicates the displacement of the Ti/Nb(2) cations in the ab plane, and no displacement of the Ti/Nb(1) cations exists in the ab plane. The results show that this material has two types of octahedral, first octahedron with little deformation around the Ti1/Nb1 and the second octahedron are more distorted around the Ti2/Nb2. The measurements of permittivity and dielectric losses of the ceramic samples performed between 25°C and 700°C (100Hz to 1MHz), high dielectric constants (ε r =127 ~ 194) and low dielectric losses (tan(δ) around 10-4 at 1MHz) were found. The maximum value of the dielectric constant is obtained for x=0 (ε r =194). The Curie temperature Tc decreases from 332 to 246°C as a function of the substitution of the samarium by neodymium. Detailed microstructural analysis by scanning electron microscope (SEM) and (EDS) for this compounds are also investigated.
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Soumis le : lundi 20 juillet 2020 - 17:48:20
Dernière modification le : mardi 21 juillet 2020 - 05:09:32
Archivage à long terme le : : mercredi 23 septembre 2020 - 20:27:38

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HAL Mor. J. Chem. 8 N°1 (2020...
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Karim Courti, Pascal Marchet, Youssef Elhafiane, Amine Bendahhou, S. El Barkany, et al.. Relationships between crystalline structure and dielectric properties in Sr 2 Sm (1-x) Nd x Ti 2 Nb 3 O 15 ceramics. Moroccan journal of chemistry, Université Mohamed Premier, 2020, 8 (1), pp.304 - 317. ⟨hal-02863452⟩

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