{sup 17}O NMR studies of local structure and phase evolution for materials in the Y{sub 2}Ti{sub 2}O{sub 7}-ZrTiO{sub 4} binary system

Journal Article · Sun Jul 15 04:00:00 EDT 2007 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2007.04.027· OSTI ID:21015889

{sup 17}O MAS NMR and XRD studies of precursor-derived Y{sub 1.6}Zr{sub 0.4}Ti{sub 2}O{sub 7.2} and Y{sub 1.2}Zr{sub 0.8}Ti{sub 2}O{sub 7.4} have been performed to investigate the development of local and long-range order in these materials as they evolve from a metastable amorphous state upon heating. Zirconium titanate (ZrTiO{sub 4}) was also investigated to help interpret the {sup 17}O NMR spectra of the ternary compositions. Consistent with earlier studies, crystallization was observed at 800 deg. C to form a fluorite structure and a small amount of rutile; weak broad reflections were also observed which were ascribed to the presence of small pyrochlore-like ordered domains or particles within the fluorite phase. As the temperature was increased further, the sizes of these domains grew along with the concentration of rutile. At the highest temperature studied (1300 deg. C), the reflections of the thermodynamic phases, pyrochlore and zirconium titanate (ZrTiO{sub 4}), dominated the XRD pattern. The {sup 17}O NMR spectra revealed a series of different peaks that were assigned to different 3- and 4-coordinate O local environments. The data were consistent with the formation of a metastable phase Y{sub 2-} {sub x} Zr {sub x} Ti{sub 2-} {sub y} Zr {sub y} O{sub 7+} {sub x} with pyrochlore-like ordering but with Zr substitution on both cation sites of the pyrochlore structure. At low temperatures, doping on the A (Y{sup 3+}) sites predominates (i.e., x>y), consistent with the fact that the pyrochlore develops out of a more disordered fluorite-like, phase. As the temperature is raised, the Zr doping on the A site decreases and the metastable phase at this temperature can now be written as Y{sub 2-} {sub x} {sub '}Zr {sub x} {sub '}Ti{sub 2-} {sub y} {sub '}Zr {sub y} {sub '}O{sub 7+} {sub x} {sub '} (i.e., x'<y'); TiO{sub 2} is also observed, consistent with this suggestion. At high temperatures, doping on the B site decreases and the resonances due to the stoichiometric pyrochlore yttrium titanate (Y{sub 2}Ti{sub 2}O{sub 7}) dominate the NMR spectra. Weaker {sup 17}O NMR resonances due zirconium titanate (ZrTiO{sub 4}) are also observed. - Graphical abstract: Schematic of the evolution of the crystalline phases in a material with stoichiometry Y{sub 1.6}Zr{sub 0.4}Ti{sub 2}O{sub 7.2} (10Zr), as a function of heat treatment at 800, 1000 and 1300 deg. C.

• OSTI ID: 21015889
• Journal Information: Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: 7 Vol. 180; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
AMORPHOUS STATE
CRYSTALLIZATION
HEAT TREATMENTS
METASTABLE STATES
NMR SPECTRA
NUCLEAR MAGNETIC RESONANCE
OXYGEN IONS
PYROCHLORE
RUTILE
TEMPERATURE RANGE 1000-4000 K
TITANATES
TITANIUM OXIDES
X-RAY DIFFRACTION
YTTRIUM COMPOUNDS
YTTRIUM IONS
ZIRCONATES