Nanocrystalline barium titanate (BTO3) powders annealed at 1050 • C for 4 h, were synthesized using the sol-gel method and the effects of Sn 4+ /Er 3+ co-doping (BTSO3:2Er) on microstructure and dielectric properties of BTO3 powders, were investigated. The crystalline structure, microstructure, molecular structure, and dielectric properties were investigated using X-ray powder diffraction, field emission scanning electron microscope, with energy dispersive X-ray analysis, the Fourier transform infra-red spectroscopy, and dielectric spectrometer. X-ray powder diffraction analysis confirmed the formation of both BTO3 and BTSO3:2Er in a single tetragonal phase. For BTSO3:2Er sample, the particle size decreased from 64 for pure BTO3 to 57.11 nm for BTSO3:2Er, inhibiting grain growth upon co-doping with Sn 4+ /Er 3+ ions. Further, according to field emission scanning electron microscope observations, the Fourier transform infra-red spectroscopy analysis showed a new band assigned to M-O. Correspondingly, BTSO3:2Er showed an anomaly relaxation peak whose maximum was positioned at temperature value (174 • C) higher than the Curie temperature (TC) according to permittivity measurements. Its TC shifted from 125 to 103 • C and permittivity considerably increased to become ten times greater than that of pure BTO3, revealing enhancements of dielectric properties upon doping with Sn 4+ /Er 3+ ions. Also, AC conductivity for BTSO3:2Er sample considerably increased due to the formation of excess oxygen vacancies.

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Nano-structure BaTi 0.9 Sn 0.1 O 3 (BTSO) doped with Nd 3+ (BTSO: 5N) and co-doped with Nd 3+ /Yb 3+ ions (BTSO: 5NY), were prepared using the modified sol-gel method in powder form and annealed at 1050 o C in air for 4h. Their structural, morphological, photoluminescence and dielectric properties studies were investigated. The crystallite sizes from XRD and TEM found to be decreased upon doping with Nd 3+ and Nd 3+ /Yb 3+ ions, respectively. FTIR results showed enhancement of crystallinity and absence of carbonates upon increasing Yb 3+ ions. TEM micrographs show that particles have spherical shape with small size within the nano-structure phase. FESEM microphotographs showed a density increase due to replacement of Nd 3+ and Yb 3+ ions at the B-site (Ti 4+ ). From photoluminescence it was obtained that emissivity quenched by increasing Yb 3+ ions concentration as the Nd 3+ act as sensitizer for Yb 3+ . Cuire temperature (T c ) of doped and codoped samples shifted to lower values. Besides, their permittivity and AC conductivity increased in comparison with BTSO.

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