Structural Transformations and Disordering in Zirconolite (CaZrTi₂O₇) at High Pressure

Abstract

Abstract:There is interest in identifying novel materials for use in radioactive waste applications and studying their behavior under high pressure conditions. The mineral zirconolite (CaZrTi 2 O 7 ) exists naturally in trace amounts in diamond-bearing deep-seated metamorphic/igneous environments, and it is also identified as a potential ceramic phase for radionuclide sequestration. However, it has been shown to undergo radiation-induced metamictization resulting in amorphous forms. In this study we probed the high pressure structural properties of this pyrochlore-like structure to study its phase transformations and possible amorphization behavior. Combined synchrotron X-ray diffraction and Raman spectroscopy studies reveal a series of high pressure phase transformations. Starting from the ambient pressure monoclinic structure an intermediate phase with P2 1 /m symmetry is produced above 15.6 GPa via a first order transformation resulting in a wide coexistence range. Upon compression to above 56 GPa a disordered metastable phase III with a cotunnite-related structure appears that is recoverable to ambient conditions. We examine the similarity between the zirconolite behavior and the structural evolution of analogous pyrochlore systems under pressure.

Pressure‐Tuneable Visible‐Range Band Gap in the Ionic Spinel Tin Nitride

“…However, while computation predicts and annealing demonstrates a discontinuous closure of the band gap across the first‐order transitions into the P 2 1 / c and the R c phases, pressure‐mediated band gap opening is present in each of the structures. As such, a likely reason for the turning point in the optical band gap above 100 GPa is not a crystalline phase change, but rather a pressure‐induced amorphisation owing to anisotropic strain, which is a consequence of the large energetic difference between Fd m and the ground state at these pressures, reinforcing the need for thermal annealing.…”

Investigation of CeTi2O6- and CaZrTi2O7-containing glass–ceramic composite materials

“…The zirconolite crystal structure forms a monoclinic system that is made up layers of TiO 6 and TiO 5 polyhedra with Ca 2+ (8 coordinate) and Zr 4+ (7 coordinate) ions located in the large interstitial sites between these layers (Figure 1b). 39 The objective of this study is to understand how ceramic crystallites behave within a glass matrix, and to investigate how the local structure of these composite materials change as a result of synthesis conditions. Borosilicate and Fe-Al-borosilicate glass-ceramic composites containing brannerite (CeTi 2 O 6 ) or zirconolite (CaZrTi 2 O 7 ) crystallites were synthesized at D r a f t different annealing temperatures to study the effect of composition and annealing temperature on the local and long-range structure of these materials.…”

Investigation of the stability of glass-ceramic composites containing CeTi2O6 and CaZrTi2O7 after ion implantation

“…The zirconolite crystal structure forms a monoclinic system that is made up layers of TiO6 and TiO5 polyhedra with Ca 2+ (8 coordinate) and Zr 4+ (7 coordinate) ions located in the large interstitial sites between these layers (Figure 1b). 39 The objective of this study is to understand how ceramic crystallites behave within a glass matrix, and to investigate how the local structure of these composite materials change as a result of synthesis conditions. Borosilicate and Fe-Al-borosilicate glass-ceramic composites containing brannerite (CeTi2O6) or zirconolite (CaZrTi2O7) crystallites were synthesized at different annealing temperatures to study the effect of composition and annealing temperature on the local and long-range structure of these materials.…”