Zirconolite, CaZr _x Ti_3−x O₇; structure refinements for near-end-member compositions with x = 0.85 and 1.30

Synthesis, Characterization, and Crystal Structure Refinement of Lanthanum and Yttrium Substituted Polycrystalline 2M Type Zirconolite Phases: Ca1-xMxZrTi2O7(M = Y, La andx= 0.2)

“…The M-O distances and O-M-O angles match with the earlier investigations on single crystal of zirconolite [26]. Figure 4 shows the PLATON projection of molecular structure depicting the interlinking of CaO 8 , ZrO 7 , and TiO 6 /TiO 5 polyhedra in the framework of zirconolite structure.…”

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

“…[3][4][5][6][7] Intergrowth defects are also commonly observed giving rise to variation in the stacking relationship between adjacent structural modules. The occurrence of polytypes and intergrowth defects thus depends sensitively on the chemical composition, and even a small concentration of dopant species (particularly rare earth cations) may be sufficient to result in complex intergrowth defects that are not readily detectable using X-ray powder diffraction techniques.…”

“…[3][4][5][6][7] Writing the general zirconolite structure as ABC 2 O 7 , the HTB layers comprise two octahedral sites (C1 and C3) forming six membered rings, within which are located five-coordinate (C2) sites that are 50% occupied; the A and B cation sites are 8-and 7-coordinate, respectively, and form an ordered array between the HTB layers. [3][4][5][6][7] Various zirconolite polytypes with complex superstructures have been described depending upon the cation site occupancy, vacancy distribution and relative displacement of HTB layers. [3][4][5][6][7] Figure 1.…”

“…[3][4][5][6][7] Various zirconolite polytypes with complex superstructures have been described depending upon the cation site occupancy, vacancy distribution and relative displacement of HTB layers. [3][4][5][6][7] Figure 1. Structural model of the starting ambient phase of CaZrTi 2 O 7 (C2/c).…”

“…1,2 The zirconolite structure can be considered as a derivative of the A 2 B 2 O 7 pyrochlore structure, where A and B represent large 8-coordinate and small 6-coordinate cations, respectively ( Figure 1). [3][4][5][6][7] The zirconolite and pyrochlore structures share a common hexagonal tungsten bronze (HTB) motif, forming (111) planes in the cubic (Fd-3m) pyrochlore structure. Compression along the [111] direction of the pyrochlore structure results in the monoclinic (C2/c) zirconolite-2M structure, in which the HTB layers lie perpendicular to the [001] direction.…”