1 Goals : • decrease diffusion paths • shorten reaction times • decrease reaction temperatures Intimate mixing of components in solution, precipitation, filtration, washing, drying, calcination  High degree of homogenization  Large contact area  Reduction of diffusion distances  Faster reaction rates  Lower reaction temperatures  Metastable phases, smaller grain size, larger surface area  Shaping to fibers, films, nanoparticles Precursor Methods 2 Coprecipitation Method Coprecipitation applicable to nitrates, acetates, oxalates, hydroxides, alkoxides, beta-diketonates Requires: similar salt solubilities similar precipitation rates no supersaturation Washing: water, organic solvents Drying: evaporation azeotropic distillation freeze-drying Disadvantage: difficult to prepare high purity, accurate stoichiometric phases if solubilities do not match 3 Coprecipitation Method LDH = layered double hydroxides (hydrotalcites) Mg6Al2(OH)16CO3.4H2O Mg(NO3)2· 6H2O + Al(NO3)3 9H2O aqueous solutions low supersaturation addition of an NaOH solution pH during precipitation kept constant at 9.0 suspension aged at 373 K for 15 h w/stirring centrifugation, washing, drying 4 Coprecipitation Method 5 Coprecipitation Method 6 Coprecipitation Method Oxalate Coprecipitation 7 LiMPO4 (M = Mn, Fe, Co, or Ni) • olivine structure • new cathode materials for lithium rechargeable batteries • multicomponent olivine cathode materials LiMn1/3Fe1/3Co1/3PO4 Mn1/3Fe1/3Co1/3(C2O4) 3 2H2O stoichiometric, homogeneously mixed transition metal oxalate precursor the differences in chemical behavior of Fe, Co, and Mn ions • control of pH - different solubilities of MC2O4 2H2O • control of atmosphere - Fe2+ get easily oxidized to Fe3+ • control of temperature and aging time - FeC2O4·2H2O and CoC2O4·2H2O have temperature-dependent polymorphisms: monoclinic α (90 C) and orthorhombic β (25 C), MnC2O4·2H2O forms only monoclinic Solid state reaction of Mn1/3Fe1/3Co1/3(C2O4) 3 2H2O and LiH2PO4 8 Pechini and Citrate Gel Method Aqueous solution of metal ions Chelate formation with citric acid Polyesterification with polyfunctional alcohol on heating Further heating leads to resin, transparent glassy gel calcination provides oxide powder Control of stoichiometry by initial reagent ratio Complex compositions, mixture of metal ions Good homogeneity, mixing at the molecular level Low firing temperatures 9 Pechini and Citrate Gel Method HOCH2CH2OH Chelation Complexation-coordination polymers Polyesterification polycondensation 10 Pechini and Citrate Gel Method 11 Double salts of known and controlled stoichiometry such as: Ni3Fe6(CH3COO)17O3(OH).12Py Burn off organics 200-300 oC, then 1000 oC in air for 2-3 days Product highly crystalline phase pure NiFe2O4 spinel Good way to make chromite spinels, important tunable magnetic materials Juggling the electronic-magnetic properties of the Oh and Td ions in the spinel lattice Double Salt Precursors Double Salt Precursors 12 13 Single Source Precursors Known phases in Cr-P system: Cr3P, Cr2P, Cr2P7, CrP, CrP2, CrP4 • Compounds containing desired elements in a proper stoichiometric ratio • Easy chemical pathway for ligand removal CrP Thermolysis 180 °C for 1 h Hexadecylamine (HDA) Oleic acid (OlA) Mesitylene 14 Vegard law behavior: A linear relationship exists between the concentration of the substitute element and a property of a solid-solution, e.g. the size of the lattice parameters. Any property P of a solid-solution member is the atom fraction weighted average of the end-members The composition of the A1-xBx alloy can be calculated from Vegard’s law The lattice parameter of a solid solution alloy a will be given by a linear dependence of lattice parameter on composition: a(A1-xBx) = x a(B) + (1-x) a(A) Vegard’s Law 15 Vegard’s Law c(CdSe1-xSx) = x c(CdS) + (1-x) c(CdSe) Anion radius S2 1.84 Å Se2 1.98 Å a hexagonal wurzite structure a cubic zinc blende a high pressure form with the NaCl structure 16 La1-xCexCrO3 17 Flux Method Molten salts (inert or reactive), oxides, metals MNO3, MOH, (M = alkali metal) FLINAK: LiF-NaF-KF M2Qx (M = alkali metal, Q = S, Se, Te) • molten salts - ionic, low mp, eutectics, completely ionized • act as solvents or reactants, T = 250-550 C • enhanced diffusion, reduced reaction temperatures in comparison with powder method • products finely divided solids, high surface area (SA) • slow cooling to grow crystals • separation of water insoluble product from a water soluble flux • incorporation of the molten salt ions in product prevented by using salts with ions of much different sizes than the ones in the product (PbZrO3 in a B2O3 flux) 18 FLINAK: LiF-NaF-KF 19 Flux Method 20 Flux Method 21 Flux Method Electrolysis in molten salts Reduction of TiO2 pellets to Ti sponge in a CaCl2 melt at 950 C O2- dissolves in CaCl2, diffuses to the graphite anode insulating TiO2  TiO2-x conductive graphite anode anodic oxidation 2 O2-  O2 + 4 ecathode TiO2 pellet cathodic reduction Ti4+ + 4 e-  Ti 22 Ionic Liquids 23 Ionic Liquids 24 Ionic Liquids 25 Synthesis of Ionic Liquids NR3 + RCl  [NR4]+ Cl Aluminates [NR4]+ Cl + AlCl3  [NR4]+ [AlCl4] Metal halide elimination [NR4]+ Cl + MA  MCl + [NR4]+ A Reaction with an acid [NR4]+ Cl + HA  HCl + [NR4]+ A Ion exchange [NR4]+ Cl + Ion exchanger A  [NR4]+ A 26 Halogenoaluminate(III) Ionic Liquids The most widely studied class of IL High sensitivity to moisture – handling under vacuum or inert atmosphere in glass/teflon RCl + AlCl3  R+ [AlCl4] 2 [AlCl4]  [Al2Cl7] + Cl autosolvolysis Keq = 1016 to 1017 at 40 ºC 2 [Al2Cl7]  [Al3Cl10] + [AlCl4] Acidic: excess of AlCl3 as [Al2Cl7] x(AlCl3) > 0.5 Basic: excess of Cl x(AlCl3) < 0.5 Neutral: [AlCl4] x(AlCl3) = 0.5 27 Equilibria in Halogenoaluminate(III) IL Equilibria in IL X1 = Cl X4 = [AlCl4] X7 = [Al2Cl7] X10 = [Al3Cl10] X13 = [Al4Cl13] X6 = Al2Cl6 28 Halogenoaluminate(III) Ionic Liquids 2 [AlCl4]  [Al2Cl7] + Cl autosolvolysis Keq = 1016 to 1017 at 40 ºC Acidic IL with an excess of AlCl3 HCl + [Al2Cl7]  H+ + 2 [AlCl4] Proton extremely poorly solvated = high reactivity Superacid [EMIM]Cl/AlCl3/HCl H0 = -19 (HSO3F: H0 = -15) Latent acidity MCl + [Al2Cl7]  M+ + 2 [AlCl4] buffered IL B + M+ + [AlCl4]  MCl + B-AlCl3 29 Superacidity 30 Superacidic [EMIM]Cl/AlCl3/HCl log Kb in HF I = not protonated II = slightly protonated III and IV = 10-20 % V = 75-90% VI-VIII = nearly completely IX and X = completely 31 Compound mp (K) Compound mp (K) Na13[La(TiW11O39)2] 253.0 Na13[Tm(TiW11O39)2] 260.2 Na13[Ce(TiW11O39)2] 263.0 Na13[Yb(TiW11O39)2] 267.2 Na13[Pr(TiW11O39)2] 253.0 Na5[CrTiW11O39] 261.5 Na13[Sm(TiW11O39)2] 256.0 Na5[MnTiW11O39] 253.0 Na13[Gd(TiW11O39)2] 265.1 Na5[FeTiW11O39] 257.6 Na13[Dy(TiW11O39)2] 265.2 Na6[ZnTiW11O39] 257.4 Na13[Er(TiW11O39)2] 261.0 Completely inorganic ionic liquids Ionic Liquids 32 Melting Point of Ionic Liquids Phase diagram of [EMIM]Cl/AlCl3 Melting point is influenced by: Cation – low symmetry, weak imtermolecular interactions, good distribution of charge Anion – increasing size leads to lower mp Composition – Phase diagram 33 Melting Point of Ionic Liquids 34 Density of Ionic Liquids The density of IL decreases as the bulkiness of the organic cation increases: 35 Viscosity of Ionic Liquids The viscosity of IL depends on: van der Waals interactions H-bonding 36 Solubility in/of Ionic Liquids Variation of the alkyl group Increasing nonpolar character of the cation increases solubility of nonpolar solutes. Water solubility depends on the anion water-soluble [BMIM] Br, CF3COO, CF3SO3 Water-immiscilble [BMIM] PF6 (CF3SO2)2N IL miscible with organic solvent IF their dielectric constant is above a certain limit given by the cation/anion combination Polarity by E(T)(30) scale [EtNH3][NO3] 0.95 between CF3CH2OH and water [BMIM] PF6 as methanol 37 Solubility in/of Ionic Liquids 38 Applications of Ionic Liquids Electrodeposition of metals and alloys (also nanoscopic) Al, CoAlx, CuAlx, FeAlx, AlTix Semiconductors Si, Ge, GaAs, InSb, CdTe Electrodeposition of a Bi-Sr-Ca-Cu alloy (precursor to SC oxides) Melt of MeEtImCl at 120 ºC BiCl3, SrCl2, CaCl2, CuCl2 dissolve well Constituent BiCl3 SrCl2 CaCl2 CuCl2 Concentration 0.068 0.50 0.18 0.050 (mol kg1 MeEtImCl) Substrate Al 1.72 V vs the Ag/Ag+ reference electrode 39 Applications of Ionic Liquids 40 Applications of Ionic Liquids Olefin polymerization Ethene + TiCl4 + AlEtCl2 in acidic IL Ethene + Cp2TiCl2 + Al2Me3Cl3 in acidic IL Cp2TiCl2 + [cation]+[Al2Cl7]  [Cp2TiCl] + + [cation]+ + 2 [AlCl4] Olefin hydrogenation Cyclohexene + H2 + [RhCl(PPh3)3] (Wilkinson’s catalyst)