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Synchrotron x‐ray spectroscopy investigation of the Ca 1− x Ln x ZrTi 2− x (Al, Fe) x O 7 zirconolite ceramics (Ln = La, Nd, Gd, Ho, Yb)
Author(s) -
Ji Shiyin,
Su Minhua,
Liao Changzhong,
Ma Shengshou,
Wang Zhiguang,
Shih Kaimin,
Chang ChungKai,
Lee JyhFu,
Chan TingShan,
Li Yuhong
Publication year - 2020
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.16832
Subject(s) - zirconolite , ionic radius , materials science , dopant , solubility , spectroscopy , xanes , actinide , ion , x ray spectroscopy , perovskite (structure) , analytical chemistry (journal) , phase (matter) , crystallography , doping , nuclear chemistry , chemistry , pyrochlore , physics , optoelectronics , organic chemistry , quantum mechanics , chromatography
When incorporating actinides into zirconolite for high‐level radioactive waste immobilization, Al 3+ and Fe 3+ ions generally act as charge compensators. In this study, we rationally designed a series ofCa 1 - xLn x ZrTi 2 - xAl , Fe x O 7(Ln = La, Nd, Gd, Ho, Yb) to unravel the dopant solubility and evolutions of the crystalline phase and local environment of cations through synchrotron X‐ray methods. It was found that single zirconolite phase is difficult to obtain and the fraction of perovskite have an increase with x from 0.1 to 0.9 inCa 1 - xLa x ZrTi 2 - xAl , Fe x O 7 . Formation of both zirconolite‐2M and zirconolite‐3O phases was observed inCa 1 - xNd x ZrTi 2 - xAl , Fe x O 7andCa 1 - xGd x ZrTi 2 - xAl , Fe x O 7 . Phase transformation from zirconolite‐2M to 3O occurs at x = 0.7 forCa 1 - xNd x ZrTi 2 - xAl , Fe x O 7while x = 0.9 forCa 1 - xGd x ZrTi 2 - xAl , Fe x O 7 . The solubility ofCa 1 - xHo x ZrTi 2 - xAl , Fe x O 7andCa 1 - xYb x ZrTi 2 - xAl , Fe x O 7to form single zirconolite‐2M can reach to 0.9 f.u. and 0.7 f.u., respectively. The evolution of lattice parameters of zirconolite inCa 1 - xLn x ZrTi 2 - xAl , Fe x O 7is greatly related to the ionic radii of cations and substitution mechanism among the cations. X‐ray absorption near edge spectroscopy revealed that Fe 3+ ions replace both five‐ and six‐coordinated Ti sites and the ratio of TiO 5 to TiO 6 decreases when increasing dopant concentration in theCa 1 - xHo x ZrTi 2 - xAl , Fe x O 7 . For the local environment of Zr 4+ , the major form is ZrO 7 with a trace of ZrO 8 .