TY - JOUR

T1 - Polysomatism and structural complexity

T2 - Structure model for Murataite-8C, a complex crystalline matrix for the immobilization of high-level radioactive waste

AU - Pakhomova, Anna S.

AU - Krivovichev, Sergey V.

AU - Yudintsev, Sergey V.

AU - Stefanovsky, Sergey V.

PY - 2016/4/1

Y1 - 2016/4/1

N2 - Murataite-8C, 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-43m, a = 39.105(12) Å, V = 59799(32) Å3, 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, Al25.44Ca55.96Ti282.20Mn53.72Fe17.24Zr15.00Ho36.64O823, is in good agreement with the empirical formula calculated from electronmicroprobe data, Al23.02Ca52.85Ti284.10Mn54.31Fe17.59Zr14.83Ho38.04O823. 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-3C 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.

AB - Murataite-8C, 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-43m, a = 39.105(12) Å, V = 59799(32) Å3, 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, Al25.44Ca55.96Ti282.20Mn53.72Fe17.24Zr15.00Ho36.64O823, is in good agreement with the empirical formula calculated from electronmicroprobe data, Al23.02Ca52.85Ti284.10Mn54.31Fe17.59Zr14.83Ho38.04O823. 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-3C 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.

KW - Crystal structure

KW - Murataite

KW - Polysomatic series

KW - Pyrochlore

KW - Radioactive waste immobilization

KW - Structural complexity

UR - http://www.scopus.com/inward/record.url?scp=84962909468&partnerID=8YFLogxK

U2 - 10.1127/ejm/2015/0027-2511

DO - 10.1127/ejm/2015/0027-2511

M3 - Article

AN - SCOPUS:84962909468

VL - 28

SP - 205

EP - 214

JO - European Journal of Mineralogy

JF - European Journal of Mineralogy

SN - 0935-1221

IS - 1

ER -