Synthesis Optimization of Aurivillius Phases

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Alfred University. Faculty of Ceramic Engineering. Kazuo Inamori School of Engineering.
The solid state processing, sintering behavior and conductivity of the Bi_{2}Sr_{2}Nb_{2}TiO_{12} Aurivillius phase were studied. The solid-state processing steps were investigated using X-ray powder diffraction (XRD). The in-situ formation of Bi_{2}Sr_{2}Nb_{2}TiO_{12} was measured using high temperature X-ray powder diffraction (HTXRD). Bi_{2}Sr_{2}Nb_{2}TiO_{12}, SrTiO_{3}, two and four-layer Aurivillius phases formed with this in-situ technique. Rietveld refinement was used to characterize the Aurivillius unit cell, and to model four-layer Aurivillius impurities. A weighted residual of 0.14 and a χ2 of 4.5 was obtained. The refined lattice parameters for Bi2Sr2Nb2TiO12 were a=3.8927(7) Å, and c=33.1960(9) Å for a body centered tetragonal unit cell with the I4/mmm space group. Rietveld refinement was used to confirm the unit cell of the δ-Bi_{2}O_{3} present in certain samples. The refined lattice parameter for the δ-Bi_{2}O_{3} was a = 5.5747(4) Å with a cubic crystal system and a space group of Fm-3m. A designed statistical study on density and affect of the sintering accelerator Bi_{2}O_{3} was completed. The model had an R2 of 0.93 and a Sy.x of 0.33, and suggested that an optimum sintering temperature was ~1060°C with approximately four weight percent Bi_{2}O_{3} added to the Aurivillius phase. The scanning electron microscope (SEM) and energy dispersion spectroscopy (EDS) were used to investigate the microstructure and identify secondary phases when necessary. The conductivity of Bi_{2}Sr_{2}Nb_{2}TiO_{12} and samples with Bi_{2}O_{3} added to the Aurivillius phase were explored using impedance spectroscopy (IS). The addition of Bi_{2}O_{3} greatly enhanced the conductivity values of the Bi_{2}Sr_{2}Nb_{2}TiO_{12} to the magnitude of the current ionic conductor standard, yittria stabilized zirconia.
Synthesis, Optimization, Aurivillius phases, Ceramics