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Title Structures and stabilities of trivalent and tetravalent rare earth ions in sevenfold and eightfold coordination in fluorite-related complex oxides
Creator/Author Morss, L.R.
Publication Date1991 Dec 31
OSTI IdentifierOSTI ID: 10110589; Legacy ID: DE92005237
Report Number(s)ANL/CP--73404; CONF-911109--6
DOE Contract NumberW-31109-ENG-38
Other Number(s)Other: ON: DE92005237
Resource TypeConference
Specific TypeTechnical Report
Resource RelationConference: Fall meeting of the European Materials Research Society (EMRS),Strasbourg (France),5-8 Nov 1991; Other Information: PBD: [1991]
Research OrgArgonne National Lab., IL (United States)
Sponsoring OrgUSDOE, Washington, DC (United States)
Subject37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 36 MATERIALS SCIENCE; TRANSITION ELEMENT COMPOUNDS; REDOX REACTIONS; OXIDE MINERALS; THERMAL GRAVIMETRIC ANALYSIS; CERIUM OXIDES; PRASEODYMIUM OXIDES; TERBIUM OXIDES; X-RAY DIFFRACTION; LATTICE PARAMETERS
Description/Abstract This paper reports the preparation and characterization of a series of oxides containing 3+ or 4+ lanthanide (M = Ce, Pr, or Tb) ions, with different ionic sizes and varying M{sup 4+}/M{sup 3+} reduction potentials, in nearly cubic coordination. The objective of the study was to demonstrate how oxidation-reduction characteristics and ionic size trends explain the properties of these oxides and to compare the oxidation-reduction stability of M{sup 3+} and M{sup 4+} lanthanide ions in high (CN 7 or 8) coordination in fluorite-related oxides versus low (CN 6) coordination in perovskite oxides. Efficient preparative methods are reported, as well as powder diffraction and thermogravimetric measurements for oxides CaMTi{sub 2}O{sub 7-x} and CaMZr{sub 2}O{sub 7-x}. These oxides were characterized by X-ray powder diffraction and by thermogravimetric analysis. CaCeTi{sub 2}O{sub 7} is a pyrochlore, a = 10.142(4) {Angstrom}, with Ce{sup 4+} much more easily reducible than in the perovskite BaCeO{sub 3}. By contrast, a preparation with the stoichiometry ``CaPbTi{sub 2}O{sub 7-x}`` is a two-phase mixture-of perovskite CaTiCo{sub 3} and a presumably Pr{sup 3+}-rich pyrochlore Pr{sub 2}Ti{sub 2}O{sub 7}(?). CaTbTi{sub 2}O{sub 7-x} appears to be a Tb{sup 3+} pyrochlore, a = 10.149(2) {Angstrom}. CaCeZr{sub 2}O{sub 7} is a pyrochlore, a = 10.524(1) {Angstrom}. A preparation of ``CaPbZr{sub 2}O{sub 7-x}`` also appeared to yield a two-phase mixture, perovskite CaZrO{sub 3} and pyrochlore Pr{sub 2}Zr{sub 2}O{sub 7}. In this paper, the structures, f-element ion sites, and M(4)-M(3) stability trends in the CaMTi{sub 2}O{sub 7-x} and CaMZr{sub 2}O{sub 7-x} oxides are compared with the structural and stability trends in the perovskites BaMO{sub 3} which have M{sup 4+} ions in sixfold (tilted octahedra) coordination.
Country of PublicationUnited States
LanguageEnglish
FormatSize: 8 p.
AvailabilityOSTI; NTIS; GPO Dep.
System Entry Date2008 Jun 19

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