A Study of the Microchemistry of Nanocrystalline BaTiO3 with Tetragonal and Pseudocubic Room Temperature Symmetries
Date
2007-09
Authors
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Publisher
New York State College of Ceramics at Alfred University. Kazuo Inamori School of Engineering.
Abstract
The investigation of possible effects of undesired surface species on barium
titanate, one of the most utilized ferroelectric ceramics, constitutes the focus of
this work. Six commercial barium titanate powders from three manufacturers
representing two different synthesis processes, with average particle sizes from
40 nm to 470 nm, were analyzed in this study. Four of the nanopowders
exhibited pseudocubic room temperature symmetry. Diffuse Reflectance Infrared
Fourier Transform (DRIFT) spectroscopic analysis of the nanopowders was
conducted in ambient atmosphere at room temperature. High temperature
DRIFT followed incorporating four avenues of analysis: moisture adsorption
studies, deuterium oxide exchange studies, carbon dioxide adsorption studies,
and high temperature analysis under dry air and UHP nitrogen atmospheres. At
the highest temperature used in this study, 1173K, moisture and the
accompanying incorporated protonic impurities were still present. The powders
readily readsorbed moisture during rapid cooling, 170K/minute, to room
temperature. The smallest powder, as received, formed spherical agglomerates
up to 10 μm diameter. These sintered as separate units attaining diameters up to
60 μm during intermediate stage sintering. X-ray photoelectron spectroscopy
indicated a surface contamination layer of 10 Å to 18 Å; 50 – 70% of which was
barium carbonate, the balance being atmospheric adsorbed species. Samples
cooled at 3K/minute after an 1173K calcine retained cubic symmetry as indicated
with high temperature X-ray diffraction. However, spectral evidence was
obtained indicating that upon the rapid cooling from the 1173K calcine, a
reorientation to the room temperature tetragonal symmetry was observed.
Further, SEM and TEM supported this finding with visual evidence of interfacial
rearrangement including corroborating electron diffraction analysis. This data,
therefore, substantiated the hypothesis that the cause of the room temperature
pseudocubic structure was strain due to the presence of point defects from
protonic impurities in conjunction with the strain between the barium carbonate
contamination layer and the barium titanate core.
Description
Advisory committee members: Robert Condrate, Steven Pilgrim, Scott Misture. Dissertation completed in partial fulfillment of the requirements for the degree of Doctorate of Philosophy in Ceramics at the Kazuo Inamori School of Engineering, New York State College of Ceramics at Alfred University
Type
Thesis