Excess electron microprobe

The polycrystalline sample in which superconductivity at temperatures in excess of 9SK was first observed consisted of two major phases. Electron microprobe analyses indicated that a green transparent phase, which comprised the majority of the early samples, contained Ba, Cu and Y in the ratios 1 1 2. A single crystal diffraction study and structure solution by direct methods indicated that this green phase has an ideal composition Y2BaCuOs, and a structure similar to that reported on the basis of powder diffraction (3). Crystallographic data for this structure are reported in Table I. 

The hydrated electron represents a ubiquitous entity in irradiated aqueous solutions, and its experimental discovery by pulse radiolysis has raised considerable interest in investigations of electron-transfer reactions in chemistry and radiobiology (i, 47-49). The dynamical component of an excess electron in a polar solution is directly dependent on transient electron-solvent couplings. The excess electron is equivalent to a microprobe that can test the inhomogeneous structures of a reaction area. This elementary charge exhibits several delo-cahzed or localized states in the condensed phase 14, 16, 18, 29). 

The electron microprobe s detection limit for Pb can be a limitation in the precision of the chemical age results (e g., Olsen and Livi 1998) as can potentially the assumption that monazite is generally concordant (eg., Cocherie et al. 1998) and does not incorporate appreciable amounts of Pb° during growth (e g., Scherrer et al. 2000). Finger and Helmy (1998) suggest that monazite is resistant to post-crystallization disturbance and mostly free from inheritance. These assumptions are not always met as numerous studies indicate that the mineral can accumulate excess ° T b (Scharer 1984, Parrish 1990, Scharer et al. 1990, see also Fig. 2), Pb° (e g., Coleman 1998, Catlos et al. 

TEM observations document the presence of distinct areas of modulated microstructure in fossil and Recent brachiopod shells. This is the first record of modulated texture in extant skeletal carbonate. There are unresolved differences of opinion regarding the underlying mechanism of formation of modulated microstructures. Although, most modulated microstructure has been associated with diagenesis, the presence of the modulated structure in Recent brachiopods eliminates a diagenetic environment as a requirement for the formation of the texture in brachiopods. Furthermore, electron microprobe measurements indicate that the calcite studied is composed of low-magnesium calcite. Thus, no major cation substitutions, such as excess Mg+ in the lattice, are responsible for the modulated microstructures in brachiopod calcite. The two most likely explanations for modulated microstructure in brachiopod calcite... 

Eugster, Albee, Bence, Thompson and Waldbaum (1972). Electron microprobe data on the compositions of synthetic muscovite -paragonite pairs produced in hydrothermal experiments are fitted to a third-order Margiiles expression for the excess Gibbs free energy using the technique of Thompson and Waldbaum (1969b). 

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