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Barkany, S. El
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Publications (3/3 displayed)
- 2020Grafting of Biodegradable Polyesters on Cellulose for Biocomposites: Characterization and Biodegradation
- 2020Relationships between crystalline structure and dielectric properties in Sr2Sm(1-x)NdxTi2Nb3O15 ceramics
- 2018A New Equation between Surface Tension and Solubility Parameters of Cellulose Derivatives depending on DS: Application on Cellulose Acetate
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article
Relationships between crystalline structure and dielectric properties in Sr2Sm(1-x)NdxTi2Nb3O15 ceramics
Abstract
In this study, tungsten-bronze type materials of Sr2Sm(1-x)NdxTi2Nb3O15 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≈579,03Ǻ 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)O6 and the Ti/Nb(2)O6 octahedra. Besides, the unequal Ti/Nb(2)–O bonds length in the equatorial plane of Ti/Nb(2)O6 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 (εr=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 (εr=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.