A LANTHANIDE LANTHOLOGY (.pdf) - Davidson Physics
A LANTHANIDE LANTHOLOGY (.pdf) - Davidson Physics A LANTHANIDE LANTHOLOGY (.pdf) - Davidson Physics
Compounds of the perovskite, ABO 3 , type, with tri-valent cations, A = Ln 3+ and B = Mn 3+ ,are recognized within the Ln-Mn-0 system for all members of the lanthanide series.Thermodynamic data have been reported[1]. These materials are ternary oxides and do not contain- as the labels, manganites and manganates, tend to imply - discrete manganese-containing anions.All the perovskite LnMnO 3 's crystallize in the orthorhombic [GdFeO 3 ] structure, the slightlydistorted version of the ideal ABO 3 structure; in addition, with Ln = Ho to Lu, a hexagonalvariation can be formed. (A ternary oxide, La 2 MnO 4 , of the K 2 NiF 4 type with La(III) and Mn(II)valencies, can also be made.)The ABO 3 compounds can be prepared by :• solid state reaction between oxide and carbonate at ≈1200 °C,• co-precipitation from aqueous solution followed by drying and calcination,• mixing appropriate solutions, formation of polymeric precursors, drying and thermaldecomposition.The "liquid-mix" solution processes[2], using nitrates or acetates, rely on polyfunctionalorganic additives, usually hydroxy-acids[3] and frequently citrates, i.e. the Pechini technique[4],but other complexing agents[5] are possible. These additives help create an amorphous organicprecursor that can then be thermally decomposed to a fine particle powder with the constituentsintimately dispersed at the atomic level. Spray drying and spray pyrolysis are often an integral partof the process.The compounds - particularly variations on the La derivative - are currently of technologicalinterest because they are :[1] Investigation of the La-Mn-O system, M.L.Borlera and F.Abbattista, J.Less Common-Met., 1983, 92(l), 55 :Chemical Potential Diagrams for Rare Earth-Transition Metal-Oxygen Systems: 1, Ln-V-O and Ln-Mn-OSystems, H.Yokokawa et al., J.Am. Ceram. Soc., 1990, 73(3), 649[2] Mixed-Cation Oxide Powders via Polymeric Precursors, P.A.Lessing, Am.Ceram.Soc.Bull., 1989,68(5),1002[3] Hydroxy Acid-aided Synthesis of Perovskite Oxides with Large Surface Areas, Y. Teraoka et al., J.AlloysComp., 1993, 193, 70[4] Method of Preparing Lead and Alkaline-Earth Titanates and Niobates, M.Pechini, U.S.Patent 3,330,697, 11July 1967[5] Synthesis of Oxide Ceramic Powders by the Glycine Nitrate-Process, L.A.Chick et al., Mater. Lett., 1990,10(1,2),61
MANGANITES• thermodynamically stable up to≈1200 °C,• chemically inert to the same temperature,• mechanically stable as well,• electrically conductive at low and high temperatures, showing• mixed electronic and ionic conductivity.The LnMnO 3 's are p-type conductors [6] with the inherent non-stoichiometric defects beingcation vacancies. The materials can show oxygen excess, stoichiometry or oxygen deficiencydepending on oxygen partial pressure as well as Ln non-stoichiometry. Furthermore the electricalconductivity - due to the B cations and strong overlap of bonds with the O atoms - can be enhancedby doping with a lower valent cation. Strontium-doped LaMnO 3 is a frequently chosen materialbecause of its high electronic conductivity in oxidizing atmospheres. This doping increases theconductivity by creating dual valency Mn ions by increasing the Mn 4+ content by :LaMnO 3 = > La 3+ 1-x Sr 2+ x Mn 3+ 1-x Mn 4+ xO 3Ceramic fuel cells, usually termed solid oxide fuel cells (SOFC's), generate electricitydirectly from the reaction of a fuel with an oxidant, and operate at 1000°C. Of theelectrochemically-active components compatible with those severe conditions, the preferredcathode material is Sr-doped LaMnO 3 [7]. Properties, e.g. thermal expansion, can be fine tuned byvarying the Ln, the divalent dopant and the transition metal.Variations on LnMnO 3 are also of interest for their catalytic potential[8]. (The initial claimthough that they performed similarly to Pt in emission control was found to be attributable to tracesof Pt in the samples.) There is of course an interplaybetween electrochemical and catalytic properties[9]. The newer preparation process producecatalytically-active materials with stable high surface areas[10] that have possibilities in exhaustemission control[11]. The combination of novel electrical and catalytic properties offers potentialalso for sensor compositions[12].[6] Review of p-type Doped Perovskite Materials for SOFC and other Applications, H.U.Anderson, Solid StateIonics, 1992, 52, 33[7] Ceramic Fuel Cells, N.Q.Minh, J.Amer.Ceram.Soc., 1993, 76(5), 563[8] see, for example, articles in, Catalysis Today, 1990, 8(2)[9] The Electrocatalysis of Oxygen Evolution on Perovskites, J.O'M.Bockris and T.Otawaga,J.Electrochem.Soc., 1984, 131, 290 ; Electrocatalytic Properties and Nonstoichiometry of the HighTemperature Air Electrode La l-xSr xMnO 3, A.Hammouche et al., J.Electrochem.Soc., 1991, 138(5), 1212[10] Preparation of Supported La 1-xSr xMnO 3 Catalysts by the Citrate Process,H.M.Zhang et al., Appl. Cat., 1988,41,137[11] Rare Earth containing Perovskites with Catalytic properties for the Cleaning ofAutomobile ExhaustGas, A.Maijanen et al., Eur.J.Solid State Inorg. Chem., 1991, 28, 437[12] Gas Sensors, T.Kudo, Catalysis Today, 1990, 8(2), 2632
- Page 2 and 3: ALANTHANIDELANTHOLOGYPart II, M - Z
- Page 8 and 9: METALSThe lanthanides, when prepare
- Page 10: METALSMetallo-thermic oxide-reducti
- Page 13 and 14: MONAZITEMonazite, a light-lanthanid
- Page 15 and 16: NEODYMIUMNeodymium is the third mos
- Page 18 and 19: [2] Preparation, Phase Equilibria,
- Page 20 and 21: NOMENCLATURE58 - 71; the term is in
- Page 22 and 23: OXALATESAddition of oxalic acid, or
- Page 24 and 25: OXIDESCalcination in air for the th
- Page 26 and 27: OXIDESFurthermore oxides with Ln IV
- Page 28 and 29: OXYCHLORIDESThermal decomposition o
- Page 30 and 31: OXYSULFIDESAll the elements of the
- Page 32 and 33: PEROVSKITESA very wide range of mat
- Page 34 and 35: PHOSPHATESThe LnPO 4 compounds can
- Page 36 and 37: PRASEODYMIUMtransport of Pr happens
- Page 38 and 39: RESOURCESFor significant resources
- Page 40 and 41: RESOURCESSignificant new resources
- Page 42 and 43: SAMARIUMSamarium metal is made dire
- Page 44 and 45: SILICATESWithin the binary Ln 2 O 3
- Page 46 and 47: SOLVENT EXTRACTIONSome text books s
- Page 48 and 49: SULFATESLanthanide sulfates can be
- Page 50 and 51: SULFIDESThe thermochernistry of CeS
- Page 52 and 53: THULIUMThulium, the rarest of the "
MANGANITES• thermodynamically stable up to≈1200 °C,• chemically inert to the same temperature,• mechanically stable as well,• electrically conductive at low and high temperatures, showing• mixed electronic and ionic conductivity.The LnMnO 3 's are p-type conductors [6] with the inherent non-stoichiometric defects beingcation vacancies. The materials can show oxygen excess, stoichiometry or oxygen deficiencydepending on oxygen partial pressure as well as Ln non-stoichiometry. Furthermore the electricalconductivity - due to the B cations and strong overlap of bonds with the O atoms - can be enhancedby doping with a lower valent cation. Strontium-doped LaMnO 3 is a frequently chosen materialbecause of its high electronic conductivity in oxidizing atmospheres. This doping increases theconductivity by creating dual valency Mn ions by increasing the Mn 4+ content by :LaMnO 3 = > La 3+ 1-x Sr 2+ x Mn 3+ 1-x Mn 4+ xO 3Ceramic fuel cells, usually termed solid oxide fuel cells (SOFC's), generate electricitydirectly from the reaction of a fuel with an oxidant, and operate at 1000°C. Of theelectrochemically-active components compatible with those severe conditions, the preferredcathode material is Sr-doped LaMnO 3 [7]. Properties, e.g. thermal expansion, can be fine tuned byvarying the Ln, the divalent dopant and the transition metal.Variations on LnMnO 3 are also of interest for their catalytic potential[8]. (The initial claimthough that they performed similarly to Pt in emission control was found to be attributable to tracesof Pt in the samples.) There is of course an interplaybetween electrochemical and catalytic properties[9]. The newer preparation process producecatalytically-active materials with stable high surface areas[10] that have possibilities in exhaustemission control[11]. The combination of novel electrical and catalytic properties offers potentialalso for sensor compositions[12].[6] Review of p-type Doped Perovskite Materials for SOFC and other Applications, H.U.Anderson, Solid StateIonics, 1992, 52, 33[7] Ceramic Fuel Cells, N.Q.Minh, J.Amer.Ceram.Soc., 1993, 76(5), 563[8] see, for example, articles in, Catalysis Today, 1990, 8(2)[9] The Electrocatalysis of Oxygen Evolution on Perovskites, J.O'M.Bockris and T.Otawaga,J.Electrochem.Soc., 1984, 131, 290 ; Electrocatalytic Properties and Nonstoichiometry of the HighTemperature Air Electrode La l-xSr xMnO 3, A.Hammouche et al., J.Electrochem.Soc., 1991, 138(5), 1212[10] Preparation of Supported La 1-xSr xMnO 3 Catalysts by the Citrate Process,H.M.Zhang et al., Appl. Cat., 1988,41,137[11] Rare Earth containing Perovskites with Catalytic properties for the Cleaning ofAutomobile ExhaustGas, A.Maijanen et al., Eur.J.Solid State Inorg. Chem., 1991, 28, 437[12] Gas Sensors, T.Kudo, Catalysis Today, 1990, 8(2), 2632
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