Structural and magnetic properties of pyrochlore solid solutions (Y,Lu){sub 2}Ti{sub 2-x}(Nb,Ta){sub x}O{sub 7{+-}}{sub y}

Journal Article · Fri Aug 15 00:00:00 EDT 2008 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2008.03.030· OSTI ID:21128370

McQueen, T M ^[1]; Huang, Q ^[2]; Cava, R J ^[1]

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1. Department of Chemistry, Princeton University, NJ 08544 (United States)
2. NIST Center for Neutron Research, Gaithersburg, MD 20899 (United States)

The synthesis and characterization of the pyrochlore solid solutions, Y{sub 2}Ti{sub 2-x}Nb{sub x}O{sub 7-y}, Lu{sub 2}Ti{sub 2-x}Nb{sub x}O{sub 7-y}, Y{sub 2}Ti{sub 2-x}Ta{sub x}O{sub 7-y} and Lu{sub 2}TiTaO{sub 7-y} (-0.4<y<0.5), is described. Synthesis at 1600 deg. C, and 10{sup -5} Torr yields oxygen deficiency in all systems. All compounds are found to be paramagnetic and semiconducting, with the size of the local moments being less, in some cases substantially less, than the expected value for the number of nominally unpaired electrons present. Thermogravimetric analysis (TGA) shows that all compounds can be fully oxidized while retaining the pyrochlore structure, yielding oxygen rich pyrochlores as white powders. Powder neutron diffraction of Y{sub 2}TiNbO{sub 7}-based samples was done. Refinement of the data for oxygen deficient Y{sub 2}TiNbO{sub 6.76} indicates the presence of a distribution of oxygen over the 8b and 48f sites. Refinement of the data for oxygen rich Y{sub 2}TiNbO{sub 7.5} shows these sites to be completely filled, with an additional half filling of the 8a site. The magnetic and TGA data strongly suggest a preference for a Ti{sup 3+}/(Nb,Ta){sup 5+} combination, as opposed to Ti{sup 4+}/(Nb,Ta){sup 4+}, in this pyrochlore family. In addition, the evidence clearly points to Ti{sup 3+} as the source of the localized moments, with no evidence for localized Nb{sup 4+} moments. - Graphical abstract: Synthesis of pyrochlore solid solutions (Y,Lu){sub 2}Ti{sub 2-x}(Nb,Ta){sub x}O{sub 7{+-}}{sub y} under high vacuum at 1600 deg. C results in oxygen deficient, paramagnetic compounds with reduced B-site cations. Studies indicate Ti{sup 3+} as the source of the localized moments, with no evidence for localized Nb{sup 4+} moments. Annealing under O{sub 2} results in fully oxidized, oxygen excess pyrochlores as white powders. Powder neutron diffraction studies show the excess oxygen on the normally vacant 8a site.

• OSTI ID: 21128370
• Journal Information: Journal of Solid State Chemistry, Vol. 181, Issue 8; Other Information: DOI: 10.1016/j.jssc.2008.03.030; PII: S0022-4596(08)00158-8; Copyright (c) 2008 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ANNEALING
CATIONS
ELECTRONS
LUTETIUM COMPOUNDS
MAGNETIC PROPERTIES
NEUTRON DIFFRACTION
NIOBIUM COMPOUNDS
NIOBIUM IONS
OXIDES
PARAMAGNETISM
POWDERS
PYROCHLORE
SOLID SOLUTIONS
SYNTHESIS
TANTALUM COMPOUNDS
THERMAL GRAVIMETRIC ANALYSIS
TITANIUM COMPOUNDS
TITANIUM IONS
YTTRIUM COMPOUNDS