CHEMICAL SYNTHESIS AND CHARACTERIZATION OF 3-LAYER Bi_{2-y}Pb_{y}Sr_{2}Nb_{2}Ti_{1-x}Al_{x}O_{12-δ} AURIVILLIUS IONIC CONDUCTORS
Date
2003
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Alfred University. Faculty of Ceramic Engineering. Kazuo Inamori School of Engineering.
Abstract
Aurivillius phases of the type Bi_{2}Sr_{2}Nb_{2}TiO_{12} and Bi_{1.6}Pb_{0.4}Sr_{2}Nb_{2}Ti_{1-x}Al_{x}O_{12} (0.0 ≤ x ≤ 0.8) were synthesized by the polymerized complex method involving an organo-metallic precursor. The effect of raising the pH of the solution on the temperature of crystallization formation was investigated through the addition of ammonium hydroxide. Infrared (IR) and nuclear magnetic resonance (NMR) spectra were obtained at various points in the reaction to aid in developing a reaction mechanism. The spectroscopic data showed the formation of an ester as well as an amide with the addition of ammonium hydroxide after polymerizing to 170 °C. Inductively coupled plasma (ICP) spectroscopy qualitatively showed that bismuth, strontium, niobium and titanium ions were all volatilizing out with solvent evaporation. Pure Bi_{2}Sr_{2}Nb_{2}TiO_{12} was formed after heat treatment for 5 hours at 900 °C. High temperature x-ray powder diffraction showed crystalline phase formation beginning at 700 °C. Phase pure Aurivillius structures were obtained with firing temperatures as low as 700 °C when the solution pH was adjusted to 9.00. A solubility limit of aluminum was discovered for Bi_{1.6}Pb_{0.4}Sr_{2}Nb_{2}Ti_{1-x}Al_{x}O_{12} at x ≥ 0.4. For x ≥ 0.4 two additional phases that formed were identified as bismuth oxide and strontium-aluminum oxide by x-ray diffraction (XRD). Scanning electron microscope – backscattered electron (SEM-BSE) images confirmed the presence of two additional phases at x = 0.6 and x = 0.8. Total conductivity of Bi_{1.6}Pb_{0.4}Sr_{2}Nb_{2}Ti_{1- x}Al_{x}O_{12} at 1123 K ranged from 1.74 x 10-4 S•cm-1 for x = 0.0 to 4.76 x 10-3 S•cm-1 for x = 0.8 stemming from oxygen vacancy formation as well as the evolution of bismuth oxide past the solubility limit. La_{1-x}Sr_{x}CoO_{3} (0.1 ≤ x ≤ 0.9) ceramics were also synthesized by the polymerized complex method. Rietveld refinement of x-ray powder diffraction data indicated that La_{1-x}Sr_{x}CoO_{3} adopts a cubic unit cell from 0.9 ≥ x ≥ 0.7, ultimately distorting to a rhombohedral unit cell at x ≤ 0.6. The lattice parameter in the cubic unit cell ranged from 3.833(1) Å at x = 0.7 to 3.838(9) Å at x = 0.9. The lattice parameter and cell angle in the rhombohedral unit cell ranged from 5.3935(9) Å and 60.6866(9)° at x = 0.1 to 5.416(4) Å and 60.080(4)° at x = 0.6.
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Keywords
Conductors, Ionic solids, Chemical properties, Synthesis, Characterization, Aurivillius phases, Ceramics