Synthesis and study of the dielectric properties of a doped NBT type material

Rahal, Rahima (2025) Synthesis and study of the dielectric properties of a doped NBT type material. Doctoral thesis, Université Mohamed Khider (Biskra - Algérie).

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Abstract

The present study reports the fabrication of NBT-type ceramic materials with the general formula (Na0.5Bi0.5) 0.94 R 0.04Ti 0.95 (Ni0.2 Fe0.2 Sb0.6) 0.05O3 (abbreviated as NBT-RNFS), where R denotes the dopant elements La, Nd, Gd, and Y. The ceramics were synthesized via the conventional solid-state reaction method. The main objective of this study was to investigate the effect of rare earth doping on the dielectric and photocatalytic properties of novel NBT-based ceramic materials. The NBT-RNFS samples were successfully synthesized at 1150°C. Undoped NBT-NFS samples had a single rhombohedral phase, while rare earth-doped NBT-NFS samples showed a rhombohedral phase along with a pyrochlore phase. Rietveld refinement of the XRD data showed a slight shrinkage of the unit cell volume with the substitution of rare earth elements, attributed to their relatively lower ionic radii compared to the host ions. Optical bandgap analysis revealed that the fabricated perovskite samples exhibited semiconducting behavior, with measured bandgap values ranging from 2.61 to 2.80 eV. The La-doped NBT-RNFS system exhibited an impressive 83% photocatalytic dye degradation rate, substantially outperforming the 23% dye removal efficiency of the undoped material. Similarly, the Nd-doped (62% dye removal) and Y-doped (66% dye removal) NBT-RNFS ceramics also displayed enhanced photocatalytic activities under broadband solar light exposure. The La-doped NBT-RNFS composition demonstrated an exceptionally high dielectric constant (εr) of 1151.87, while the Nd-doped NBT-RNFS exhibited a dielectric constant of 1122.31. These values significantly exceeded the dielectric constant of 951.02 obtained for the undoped NBT-NFS ceramic.

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