Papers by Author: Clive A. Randall

Abstract: Re-oxidation is an important thermal process to minimize oxygen vacancies and produce high reliable Ni-MLCCs. The re-oxidation of these devices is then investigated with a series of “in-situ” impedance measurements between 400 and 500 °C in air. From the relative impedance change, chemical diffusion coefficients, associated activation energy and effective equivalent circuit model are determined. Those values were found to be reasonable compared with previous researchers’ data. Moreover, the proposed effective equivalent circuit model successfully represents the real Ni-MLCC morphology. From transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS), it is found that the electrical properties and reliabilities of the Ni-MLCCs re-oxidized under different conditions are identical.

Abstract: The microstructure and interface quality of chemical solution deposited barium titanate thin films on Ni foil were studied. Cross-sectional transmission electron microscopy shows that a ~200 nm thick barium titanate film annealed in a controlled oxygen partial pressure consists of equiaxed grains with grain size range of 24-75 nm (~ 42 nm average). NiO was detected after re-oxidation by X-ray diffraction, but not by transmission electron microscopy, suggesting that the oxide is not a continuous barrier layer, but is spatially distributed in the films. Oxygen non-stoichiometry and the existence of C in barium titanate films were observed by electron energy loss spectrometry. In addition, it was found that there is a 5-8 nm thick Ni-Ba alloy developed at the interface between the barium titanate film and Ni foil.

Abstract: There is no single mechanism of electrophoretic deposition (EPD). Just as there are several mechanisms for creating a stable colloidal suspension, there are several mechanisms by which particles can be destabilized to form an adherent deposit at an electrode surface. The goal of this paper is to provide a listing of the mechanisms by which electrophoretic deposition can occur. Several of these mechanisms have already been demonstrated, while others remain speculative. The first step in this process is to provide a clear definition of what exactly EPD is, and, equally important, to clearly distinguish EPD from three other very similar processes: electrostatic coating, electrodeposition, and electrocasting. From this definition a series of logical steps leads to a list of mechanisms by which a stable colloid can be converted to a stable particle compact.