A LANTHANIDE LANTHOLOGY (.pdf) - Davidson Physics

TITANATES / TITANIUM DIOXIDEWithin the Ln 2 O 3 / TiO 2 systems, several compounds containing Ln 3+ , Ti 4+ and O 2- , havebeen recognized[1], the more important are listed in the box. The Pyrochlore structure, forLn 2 Ti 2 O 7 species, occurs only with the smaller Ln ions; the L 2 T 9 compound can approach an LT 4composition.Ln 2 O 3 : TiO 2 CompoundsFormulaOxide Ratio(Abbreviation)StructureTypeLn Rangefor StabilityLn 4Ti 9O 24 L 2T 9 (complex)Ln 2Ti 2O 7 LT 2 Pyrochlore Ln = Sm to Lu,YLn 2Ti 2O 7 LT 2 (several) Ln = La to NdLn 2TiO 5 LT (several)L = Ln 2O 3 ; T = TiO 2These compounds can be prepared by the high-temperature solid-state reaction of mixed oxides orcarbonates, or by firing of coprecipitated material obtained, for example, by the "Pechini"citrate-process. (The stability of tetravalent Cerium causes, on firing, a brannefite-type Ce 4+ Ti 2 O 6compound to form.[2]) Possible lattice vacancies plus the potential for variable valency withtitanium means that Ln-Ti-O systems will, in general, be structurallly complex.In the systems Ln 3+ -Ti 3+ -O, with trivalent titanium, an isostructural series of Compounds forLn = La to Tm, plus Y, with the perovskite, ABO 3 , structure is formed.[3] (The compoundEuTiO 3 , due to the stability of divalent Europium, is Eu(II)-Ti(IV)-O 3 .) These perovskites have arange of novel and complex magnetic and electrical properties. Metallic and semi-conductingbehavior are possible. Virtually every type of magnetic phenomena, e.g ferro-, ferri-, antiferro-, andpara-magnetism, can be found in the series.[3][1] Lanthanide Titanates, L.G.Shcherbakova et al., Russ.Chem.Rev. (Engi. ed.), 1979, 48(3), 423[2] Crystal Chemistry of Cerium Titanates, Tantalates and Niobates, R.S.Roth et al., Mat.Res.Bull., 1977,12,1173[3] The Rare-Earth Titanium(III) Perovskite Oxides - An Isostructural Series with a Remarkable Variation inPhysical Properties, J.E.Greedan, J.Less-Common Met., 1985, 111, 33548