Radiation stability of gadolinium zirconate: A waste form for plutonium disposition

Abstract

Zirconate and titanate pyrochlores were subjected to 1 MeV of Kr+ irradiation. Pyrochlores in the Gd2(ZrxTi1-x)2O7 system (x = 0, 0.25, 0.5, 0.75, 1) showed a systematic change in the susceptibility to radiation-induced amorphization with increasing Zr content. Gd2Ti2O7 amorphized at relatively low dose (0.2 displacement per atom at room temperature), and the critical temperature for amorphization was 1100 K. With increasing zirconium content, the pyrochlores became increasingly radiation resistant, as demonstrated by the increasing dose and decreasing critical temperature for amorphization. Pyrochlores highly-enriched in Zr (Gd2Zr2O7, Gd2Zr1.8Mg0.2O6.8, Gd1.9Sr0.1Zr1.9Mg0.1O6.85, and Gd1.9Sr0.1Zr1.8Mg0.2O6.75) could not be amorphized, even at temperature as low as 25 K.

Structural properties of the geometrically frustrated pyrochloreTb2Ti2OHan1, Gardner2, Booth3 2004Phys. Rev. B513320View full textAdd to dashboardCite

“…The possibility of antisite disorder (site interchange between Tb and Ti atoms) was also considered, such as could occur if the system had a propensity toward a fluorite-like structure. 26,27 We find no evidence for any such disorder, and place an upper limit of 2% on metal-site mixing. Similarly, we performed fits al- (2) 220(10) lowing the oxygen occupancy fractions to vary, including the possibility of oxygen on the nominally vacant 8a site.…”

The low-temperature heat capacity of some lanthanide zirconates

“…Recently, they have attracted attention in the scientific world as geometrically frustrated magnetic systems, exhibiting 'spin ice' behaviour [1][2][3]. During the last decades they have found many interesting industrial applications: they are studied for thermal barrier coating [4][5][6][7], sub-catalysts for automotive exhaust gases (Ce 2 Zr 2 O 7 þ y ) [8][9][10][11] as well as for nuclear applications [12][13][14][15][16][17][18][19][20][21]. For the latter, which is the topic of our research, it is important that the chemical configuration of the lanthanide zirconate pyrochlores enables incorporation of actinides in the crystal lattice.…”

Ion-Irradiation-Induced Amorphization Of Cadmium Niobate Pyrochlore

“…GdzTi207 has been the subject of considerable study since it is one of the three main actinide-bearing phases of SYNROC, -a polyphase ceramic waste form proposed for the disposition of high-level nuclear waste. Replacement of the Gd with other lanthanide elements or Ca has been found to have a relatively minor effect on the kinetics of irradiation-induced amorphization; however, the substitution of Ti with Zr in increasing concentrations sharply increases the resistance to amorphization even at cryogenic temperatures [3]. Pyrochlore containing a variety of Asite cations, including mixtures of Ca, U, [4,5] and various lanthanides [6] are easily amorphized at room temperature, and in fact, amorphization can be induced at temperatures as high as 1030 K.…”