Phase Relations and Elemental Distributions in the Ceramics of the Pseudo-Binary Systems CaZrTi2O7 - LnAlO3 (Ln = Eu, Gd)

Zirconolite and perovskite were found to be major and minor phases respectively in the ceramics of the series (1-х) CaZrTi2O7 – x EuAlO3 and (1-х) CaZrTi2O7 – x GdAlO3 (х = 0.25; 0.5; 0.75) produced by cold pressing and sintering at 1400, 1450 and 1500 0 С. Zirconolite and cubic fianite-type oxide (in the Eu-bearing ceramics) were extra phases. At х = 0.25 major host phase for Eu and Gd is zirconolite accumulating of up to 90% of total Eu and Gd. With increase x value to 0.5 zirconolite remains major host phase for both Eu and Gd and accommodates almost 70% of total Eu2O3 and about 60% of total Gd2O3. Perovskite becomes major phase for both Eu2O3 and Gd2O3 at х = 0.75 accumulating of about 66% of total Gd2O3. As follows from SEM/EDS data Eu and Gd contents in the zirconolite may exceed ~1 formula units, therefore, zirconolite ceramics may be effective matrices for actinide fraction of HLW where Am and Cm are dominant because their crystal chemical behavior is similar to behavior of Gd.