Structural and dielectric characterization of new lead-free perovskites in the (SrTiO3)-(BiFeO3) system

Microcrystalline powders of the Sr2-xBixTi2-xFexO6 +/-delta (x=0.25; 0.50; 0.60; 0.75; 1; 1.25) perovskites have been prepared by the liquid-mix technique and the SrBiTi2-xFexO6 (x=0.85) sample was obtained by the ceramic method. Rietveld refinements from X-ray powder diffraction data showed a structural transition as a function of x: cubic symmetry (S.G. Pm3m) is observed for x <= 1 whereas the x=1.25 sample presents rhombohedral symmetry (S.G. R (3) over bar c). Refined occupations and EDX analyses indicate that the obtained cationic compositions are close to the nominal ones for the Sr2-xBixTi2-xFexO6 +/-delta samples but a small cationic deficiency was detected in the sample obtained by the ceramic method. Particle sizes of about 200 nm were obtained for the samples obtained by the liquid mix technique whereas they were clearly micrometric for the x=0.85 sample, obtained by the ceramic method. HRTEM analysis showed that these greater in size crystals present high degree of microstructural disorder. The dielectric response seems to be related to a relaxor-type ferroelectric behavior. Capacitance, conductivity and tangent loss values indicate the prevalence of intergrain conductive contribution in the electrical response. The results are comparatively analyzed in relation to microstructural features and the synthesis method employed. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.