M.S. (Master of Science)
Department of Physics
Condensed matter; Physics; Materials science
This thesis presents the results of investigation of structural and ferroelectric changes when the (Ba₁Sr)TiO₃ systems are substituted by the smaller size elements into the Ti-site, while controlling the tolerance factor value and temperature. Several chemical compositions and methods were utilized to synthesize the substituted materials at 10% level. Oxidation and reduction reactions were employed through annealing materials at wide range of temperatures and atmospheres to achieve perovskite phase. X-ray diffraction (XRD) was conducted to analyze the structure of the samples after each annealing. Temperature dependent XRD was performed to determine the structural and associated ferroelectric phase transition temperatures for selected materials in collaboration at APS synchrotron at Argonne National Laboratory. The isoelectronic substitutions of BaTi₀.₉M₀.₁O₃ with smaller size cations M = Ge⁴⁺, Mn⁴⁺, and Fe⁴⁺ were attempted based on the hypothesis that the enhancements of Curie temperature can be achieved with the increase of tolerance factor. This prediction was successfully demonstrated for Ge and Mn while it was not possible to synthesize the Fe substituted material. The analogous substitutions of SrTi₀.₉M₀.₁O₃ where M = Al³⁺V⁵⁺, Ge⁴⁺, and Mn⁴⁺ were attempted to remove ferro-distortive structural transition at 105 K and induce ferroelectricity by increasing the tolerance factor value. These single-phase materials were achieved, however, only cubic Pm-3m was observed at room temperature. The low temperature XRD experiments done for SrTi₀.₉Ge₀.₁O₃ and SrTi₀.₉Mn₀.₁O₃ by collaborators showed cubic structure down to 4 K. Therefore, the ferroelectric phase was not achieved but the ferro-distortive phase was most probably removed in agreement with tolerance factor rule.
Alfurhud, Saber, "Control of ferroelectrcity in ATiO₃ (A= Ba₁ and Sr) by isoelectronic Ti-site substitutions" (2018). Graduate Research Theses & Dissertations. 1959.
Northern Illinois University
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