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New type of paramagnetic silver clusters in sodalite: Ag8n+

Jaroslaw Sadlo 1Jacek Michalik 1Hirohisa Yamada 2Yuichi Michiue 2

1. Institute of Nuclear Chemistry and Technology (IChTJ), Dorodna 16, Warszawa 03-195, Poland
2. National Institute of Material Science (NIMS), Tsukuba, Japan


Metal clusters exhibit novel electronic, optical and chemical properties owing to quantum size effect. Small cationic silver clusters have been efficiently stabilized in zeolites after hydrogen or gamma irradiation reduction. Depending on their framework structure, cation capacity and water presence zeolites offer possibility to stabilize silver clusters with different size and charge. They can be formed in two different agglomeration pathways. In the first one the agglomeration is radiation-induced process initiated by Ag0 atoms and following by the reactions of Ag+ cations with Ag0 and later with Ag2+ and Ag32+ clusters during gradual thermal annealing. Finally Ag43+ tetramers are formed and it was postulated that they are located in octagonal prisms of zeolite rho structure.
The second agglomeration pathway was observed in Ag-A zeolite. In the course of dehydration at 150oC Ag+ become mobile and they agglomerate filling some cages with six Ag+ cations. The assembly of six Ag+ by trapping radiation-produced electron forms Ag65+ cluster which is paramagnetic and can be observed by EPR.
In the present work we investigated ~100μm crystallites of silver sodalite with hydroxyl guest anion. The XRD analysis showed sodalite structure with unit cell dimension of 0.8784 nm. Chemical composition was checked using electron microprobe analyzer and ICP technique; in both cases silver loading was higher than 7.8 per unit cell. EPR spectra of sodalite, γ-irradiated at 77K and recorded just after irradiation, show 9-line, almost isotropic signal with giso=1.987 and hyperfine splitting of 8.3 mT due to Ag8n+ cluster. Its intensity decreases during thermal annealing and signal decays completely above 200K. We tentatively postulate that octamer consists of four Ag atoms located inside sodalite cages which interact with four Ag located in hexagonal windows of adjacent sodalite cages.


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Presentation: poster at E-MRS Fall Meeting 2003, Symposium F, by Jaroslaw Sadlo
See On-line Journal of E-MRS Fall Meeting 2003

Submitted: 2003-05-27 13:35
Revised:   2009-06-08 12:55