Structural and crystal chemical properties of rare-earth titanate pyrochlores

Journal Article · Wed Jan 01 04:00:00 EST 2014 · Journal of Alloys and Compounds

DOI:https://doi.org/10.1016/j.jallcom.2014.03.153· OSTI ID:1131519

Farmer, James Matthew ^[1]; Boatner, Lynn A ^[1]; Chakoumakos, Bryan C ^[1]; Du, Mao-Hua ^[1]; Lance, Michael J ^[1]; Rawn, Claudia J. ^[2]; Bryan, Jeff C. ^[3]

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1. ORNL
2. Oak Ridge National Laboratory (ORNL)
3. University of Wisconsin

Rare-earth titanates, RE2Ti2O7 (where RE = a rare-earth) with the pyrochlore structure continue to be investigated for use as potential stable host materials for nuclear and actinide-rich wastes. Accordingly, the present work is directed towards the elucidation of the fundamental structural, physical, and thermochemical properties of this class of compounds. Single-crystals of the rare earth pyrochlores were synthesized using a high-temperature flux technique and were subsequently characterized using single-crystal X-ray diffraction. The cubic lattice parameters display an approximately linear correlation with the RE-site cation radius. Theoretical calculations of the lattice constants and bond lengths of the subject materials were carried out using density functional theory, and the results are compared to the experimental values. The Sm and Eu titanates exhibit a covalency increase between the REO8 and TiO6 polyhedra resulting in a deviation from the increasing linear lattice parameter through the transition series. Gd2Ti2O7 with the 4f7 half-filled f-orbital Gd3+ sub-shell exhibits the lowest 48f oxygen positional parameter. The coefficient of thermal expansion for the rare-earth titanate series is approximately linear, and it has a range of 10.1 11.2 x 10-6 C-1. Raman spectroscopy indicated that the ~530 cm-1 peak associated with the Ti-O stretching mode follows a general trend of decreasing frequency with increasing RE reduced mass.

• Research Organization: Oak Ridge National Laboratory (ORNL)
• Sponsoring Organization: SC USDOE - Office of Science (SC)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1131519
• Journal Information: Journal of Alloys and Compounds, Journal Name: Journal of Alloys and Compounds Journal Issue: n\a Vol. 605; ISSN 0925-8388
• Country of Publication: United States
• Language: English

Related Subjects

crystal growth
density functional theory
pyrochlores
rare earth compounds
single crystal X-ray diffraction
thermal expansion