Defects induced by electron irradiation in hollandite ceramics, specific radioactive cesium-host wasteforms: a 57Fe Mössbauer study

Abstract

Several single phase hollandite ceramics having Ba 2+ x Cs + y (C = Al,Fe) 3+ 2x+y Ti 4+ 8j2xjy O 16 composition have been synthesized and irradiated under external electron beams simulating the b-irradiation of radioactive cesium. These samples have been characterized by 57 Fe transmission Mö ssbauer spectroscopy. Mö ssbauer results show that the irradiation modifies the local arrangements of Ba cations around Fe 3+ ions by atomic displacement of Ba ions.

Synthesis and characterisation of the hollandite solid solution Ba1.2-xCsxFe2.4-xTi5.6+xO16 for partitioning and conditioning of radiocaesium

“…12,13 . However, our results are somewhat in contrast to those reported by Nguyen et al (2005) who found that Fe 3+ occupied two distinct sites in ferric Ba-Cs hollandite structures (Ba1Cs0.28Al1.46Fe0.82Ti5.72O16, the most analogous to the compositions studied in this investigation and nominally identical to that studied by Leinekugel-le-Cocq et al) and that irradiation led to the formation of a distinct third site 11 . As the tetragonal space group only has one crystallographic site for framework B cations, it is possible to speculate that the pristine samples studied by Nguyen et al were either not single phase or possibly contaminated with other Fe bearing secondary phases.…”

“…Previous work has synthesised hollandites containing iron and caesium however, the influence of varying Cs content on the local Fe structural environment has not been investigated 2,9,[11][12][13] . This study was devised to investigate the stability of the structure, in particular Fe charge compensation, with respect to Cs substitution.…”

Synthèse et stabilité sous irradiation électronique d'une céramique Ba1,16Al2,32Ti5,68O16 de structure hollandite envisagée pour le confinement de césium radioactif

“…´quent, cette e ´tude RMN montre que les irradiations e ´lectroniques induisent la formation de lacunes d'oxyge `ne autour des ions Al 3þ de la hollandite. Cela est par ailleurs en accord avec les re ´sultats que nous avons obtenus par spectroscopie Mo ¨ssbauer du fer pour une hollandite Ba 1,16 Fe 2,32 Ti 5,68 O 16 irradie ´e [10,29].…”

Effect of Synthetic Method and Annealing Temperature on the Structure of Hollandite-Type Oxides

“… − Hollandite can be found in SYNROC C (a mutli-phase ceramic nuclear waste form) and serves as a host phase for radioactive Cs . The ability of this phase to accommodate Ba 2+ , Cs + , Rb + , and Sr 2+ into the crystallographic sites in this structure makes it applicable for the immobilization of 137 Cs. − Barium titanate-type compounds that adopt the hollandite-type structure have also been proposed for use as oxidation catalysts, ion exchangers, solid ionic conductors, dielectric resonators, and battery materials. ,, …”