Phase composition of ceramics in systems with oxides of rare-earth elements, manganese, and titanium

Ceramics based on systems with oxides of rare-earth elements (REE: Y 2O3, Sm2O3, Gd2O 3), manganese, and titanium, considered as hosts for immobilization of REE- and actinide-containing radioactive wastes (RAW), were prepared by cold pressing and sintering at 1300-1400°C, and also by plasma treatment. Phases of the pyrochlore-murataite series are prevalent in the ceramics, and perovskite-pyrophanite-type phases are impurity phases, as well as the hibonite-loveringite- and garnet-type phases revealed in the ceramics prepared with addition of iron and aluminum oxides. The formation of murataite or, more precisely, of structures consisting of murataite and pyrochlore modules is more typical of the yttrium-containing systems. With an increase in the radius of the REE ion, the tendency toward formation of pyrochlore-type phases is enhanced, and the presence of large REE cations (La) stimulates formation of a perovskite-type phase. © 2007 Pleiades Publishing, Inc.