Publication Date:
2016-03-15
Description:
Murataite-8 C , a prospective synthetic material for the long-term immobilization of high-level radioactive waste and a member of the pyrochlore–murataite polysomatic series, was investigated by means of single-crystal X-ray diffraction. The crystal structure (cubic, F -43 m , a = 39.105(12) Å, V = 59799(32) Å 3 , Z = 4) is of outstanding complexity and contains forty symmetrically independent cation sites. Its crystal-chemical formula determined on the basis of the crystal-structure refinement, Al 25.44 Ca 55.96 Ti 282.20 Mn 53.72 Fe 17.24 Zr 15.00 Ho 36.64 O 823 , is in good agreement with the empirical formula calculated from electron-microprobe data, Al 23.02 Ca 52.85 Ti 284.10 Mn 54.31 Fe 17.59 Zr 14.83 Ho 38.04 O 823 . The crystal structure is based upon a three-dimensional octahedral framework that can be described as an alternation of murataite and pyrochlore modules immersed into a transitional substructure that combine elements of the crystal structures of murataite-3 C and pyrochlore. The obtained structural model confirms the polysomatic nature of the pyrochlore–murataite series and illuminates the chemical and structural peculiarities of crystallization of the murataite-type titanate ceramic matrices. The high chemical and structural complexity of the members of the pyrochlore–murataite series is unparalleled in the world of crystalline materials proposed for the high-level radioactive waste immobilization, which makes it unique and promising for further technological and scientific exploration.
Print ISSN:
0935-1221
Electronic ISSN:
1617-4011
Topics:
Geosciences
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