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The effect of Na-K ion exchange on the formation of Co nanoparticles in sodium silicate glasses doped with CoO

Lidia D. Bogomolova ,  Nina A. Krasilnikova 

M.V. Lomonosov Moscow State University, Vorobyevy gory, Moscow 119992, Russian Federation
Institute of Nuclear Physics, Moscow 119992, Russian Federation

Abstract

The aim of the present report is the study of states of Co in Co-containing sodium-silicate glasses after Na+-K+ ion exchange. The base binary 20Na2O-80SiO2 (in mol.%) glasses containing 0.5 wt.% CoO were studied. Polished plates approximately 0.4 mm thickness were prepared. The plates were immersed in a molten salt KNO3 for periods of time (Tp) varying from 5min to 7h at 450 K. Some samples were annealed after ion exchange at 600 0C for 24h in the H2 atmosphere. The asymmetric EPR line with crossing-base g=4.4 ±0.1 and DHpp~100 mT was observed at 4.2 K for the samples before an ion exchange and was attributed to Co2+ ions in distorted octahedal environment. The intensity of EPR line decreases with increasing Tp. New EPR line with g=2.31±0.02 is observed along with the g=4.4 line at 4.2K. Its width (DHpp~10-25 mT) depends on Tp. The g=2.31 line is not observed above 77 K. According to literature data we attribute the g=2.31 signal to Co1+ ions. The small width of this line is associated with exchange interactions between ions Co1+ which form clusters . We assume the existence of Co2+®Co1+ transition during the Na+® K+ ion exchange process. Starting from Tp=1 h and Tht>5h the single line with g~2.22 and DHpp~30-40 mT was observed at room temperature. The dependence of the width and intensity of this line on measurement temperature indicates its superparamagnetic origin. An additional shoulder at 265 mT which appears at 4.2K for the samples with Tp>1 h and Tht~15h indicates the formation of ferromagnetic particles of metallic Co . Optical absorption spectra and TEM of the samples confirm the formation of nano-particles of metallic Co in ion-exchange layers of heat-treated sodium- silicate glasses doped with CoO.

 

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Presentation: Oral at E-MRS Fall Meeting 2007, Symposium F, by Lidia D. Bogomolova
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-13 21:11
Revised:   2009-06-07 00:44