Highlights

Radiation Damage of Lanthanide Titanates – Ln₂TiO₅

Scientific Achievement

The lanthanide titanates offer many advantages to the study of the radiation tolerance of materials.  There is a large body of work available for comparison, but the main advantage is the ability to examine materials with differing Ln/Ti ratio’s.

La₂TiO₅, La_2/3TiO₃ and La₂Ti₂O₇ - these systems have different La/Ti ratio’s and adopt differing structures, La_2/3TiO₃ and La₂Ti₂O₇ are perovskite or perovskite related, with a range of La co-ordinations 7-12, and a Ti co-ordination of 5. La₂TiO₅, adopts a structure with atypical cation co-ordinations, in this case La=7, while Ti=5 (off centre square-based pyramid).  The radiation tolerances for these systems are markedly different, for La_2/3TiO₃ and La₂Ti₂O₇ the Tc (critical temperature for amorphisation, the temperature above the sample remains crystalline) are closely matched, 840 and 865K respectively.  However, for La₂TiO₅ the material is more prone to damage and has a higher significantly higher Tc, 1065K).  This work has been presented at the Scientific Basis for Nuclear Waste Management XXIII conference.

Y₂TiO₅, Y₂Ti₂O₇ and Yb₂TiO₅ - these systems are similar to the lanthanum titanate above, but they all adopt cubic structures based on Fd`3m symmetry, Y₂Ti₂O₇ is pyrochlore while Y₂TiO₅ and Yb₂TiO₅ are stuffed pyrochlores and can be represented as Y/Yb_2.667TI_1.333O_6.667.  In comparison with the lanthanum titanates there are similar changes, the Y₂Ti₂O₇ sample has a Tc of 664K while the Y₂TiO₅ has a Tc of 590 K.  In these systems Y₂Ti₂O₇ is more ordered that Y₂TiO₅, which has Y and Ti on the B-site (in Y₂Ti₂O₇ Y is on the A-site and Ti is on the B-site).  This would suggest that systems, which have increased disorder, recover from damage more quickly, with a lower Tc, than those that are ordered.

Significance

The results from this work have shown that a material with a high degree of structural disorder tolerates/recovers more easily than for example a material that is highly ordered e.g. La₂TiO₅. This work is being expanded to include materials which can be both ordered and disordered, e.g. partially ordered pyrochlores.

This work has been presented at the Scientific Basis for Nuclear Waste Management XXXI in Sheffield, 2007 and Structure/Property Relationships in Fluorite-Derived Compounds held at the MRS Fall Meeting in Boston 2008, and the paper was also submitted to the proceedings of that conference.

Performers

G. R. Lumpkin, K. L. Smith, M. G. Blackford, K. R. Whittle (Institute of Materials Engineering, ANTSO, Australia); N. J. Zaluzec (Argonne-MSD)