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pp.78-84
New pyrochlore-type phases(A2B2O7) were synthesized in the systems: CaO-CeO2-TiO2, CaO-UO2(ThO2)-ZrO2, CaO-UO2(ThO2)-Gd2O3-TiO2-ZrO2, 및 CaO-ThO2-SnO2. The starting materials were pressed with the pressure of 200~400 MPa and sintered at 1500~ 1550℃ for 4~8 hours in air and at 1300~ 1350℃ for 5 ~50 hours under oxygen atmosphere. The products were characterized using XRD, SEM/EDS and TEM. In the bulk compositions of CaCeTi2O7, CaThZr2O7,(Ca0.5 GdTh0.5)(ZrTi)O7) (Ca0.5GdTh0.5)(ZrTi)O7, (Ca0.5GdU0.5)(ZrTi)O7 and CaThSn2O7 , pyrochlore was the major phase, together with other oxide phase of2O7 fluorite structure. In the samples with target compositions CaUZr2O2및 Ca0.5 GdU0.5)Zr2TiO7 pyrochlore was not identified, but a fluorite-structured phase was detected. The formation factor as the stable phase depended on crystal chemical characteristics of the actinide and lanthanide elements of the system concerned.
