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Ion-Irradiation Study of the “Exotic” Mineral Neptunite: LiNa2K(Fe,Mg,Mn)2Ti2Si8O24

Published online by Cambridge University Press:  26 February 2011

Ray K. Eby ,
L. M. Wang ,
G. W. Arnold  and
R. C. Ewing
Ray K. Eby
Affiliation:
Department of Geology, University of New Mexico, Albuquerque, NM 87131
L. M. Wang
Affiliation:
Department of Geology, University of New Mexico, Albuquerque, NM 87131
G. W. Arnold
Affiliation:
Sandia National Laboratories, Albuquerque, NM 87185
R. C. Ewing
Affiliation:
Department of Geology, University of New Mexico, Albuquerque, NM 87131
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Abstract

Single crystals of the silicate neptunite were irradiated with 600 keV Ar2+ and 1.5 MeV Kr+ and analysed by transmission electron microscopy. Amorphization was observed in a surface layer several hundred angstroms thick following Ar2+ irradiations up to 5.0×l013 Ar/cm2, yet the Ar2+ ions travelled an average of 1/2 μm in depth. The microstructure of the amorphous surface layer depends on the ion fluence, but the amorphous layer thickness remained constant. At the highest fluence, a narrow region below the amorphous layer shows a brittle-to-ductile strain transition, due to tensional volume-expansion of the adjacent ductile amorphous layer. With 1.5 MeV Kr1+, amorphization of the electron transparent region was completed after a fluence of 1.7×l014 Kr+/cm2, and no further damage was observed up to 5.1×1015 Kr+/cm2. However, following a low fluence of 2.0×1011 Kr+/cm2, a single crystal of neptunite became a polycrystalline aggregate (grain size 10 nm) within 7 days of room temperature aging.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 201: Symposium A – Surface Chemistry and Beam-Solid Interactions , 1990 , 283
Copyright
Copyright © Materials Research Society 1991

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