The Study of Structure and Transitional Phases in B۰.۹۵Bi۰.۰۵Ti۱-xFexO۳ Ceramics Synthesized by Solid State Route

The structural and dielectric properties of iron and bismuth co-substituted BaTiO۳ ceramic with the formula: B۰.۹۵Bi۰.۰۵Ti۱-xFexO۳ for x=۰.۰۰ to ۱.۰۰, synthesis with solid state route, were characterized.     The X-ray diffraction results show a tetragonal phase for x=۰.۰۰. While for x=۰.۴۰ to ۰.۸۰ we observed a coexistence of tree phase tetragonal, hexagonal and pseudo-cubic. And at x=۱.۰۰ only the pseudo-cubic phase is present and the other phase disappeared. The Raman results indicate the existence of tetragonal band for x≤۰.۴۰, and an appearance of characteristic bands of Fe۳+ ions for more than ۰.۴۰ of Fe content. The SEM micrographs show an increase in grain size with the increase of Fe content and it reaches a maximum at x=۰.۴۰.  And the Mossbauer spectroscopy indicates that our samples is paramagnetic at room temperature and that the Fe is   oxidized under Fe۳+ with no existence of Fe۲+ and Fe۴+ ions. The temperature dependence of dielectric permittivity was investigated in the frequency range from ۲۰ Hz to ۲MHz. The results show three dielectric relaxation phase transitions from a rhombohedral ferroelectric to orthorhombic ferroelectric (TR-O) then to a tetragonal ferroelectric phase (at TO-T), and finally to cubic paraelectric at the Curie temperature (TC).  In addition, the temperature of phase transition shifted to the lower temperature with the increase of Fe content for all the phase transitions. And the maximum of dielectric permittivity increases for TR-O while for TT-O and Tm phases transitions, it reaches a maximum at x=۰.۶۰ and x=۰.۸۰ respectively and then decreases.

Keywords:

Structural , dielectric , BaTiO۳ , solid state , SEM , Mossbauer , paramagnetic , phase transition , curie temperature.