1 Solid State Synthesis • Solid State Reactions • Film deposition • Sol-gel method • Crystal Growth 2 • Synthesis References • The material we discussed in class was drawn primarily from the following sources: • A.R. West "Solid State Chemistry and its Applications" Chapter 2 – Preparative Methods • "Solid-State Chemistry – Techniques" Chapter 1 – Synthesis of Solid-State Materials J.D. Corbett – book edited by A.K. Cheetham and P. Day More detailed treatment, including practical details such as what sort of containers to use, how to avoid introducing impurities, what reactants to choose, etc., than above references. Corbett’s treatment is less oriented toward oxides, and more focussed on materials such as chalcogenides, halides and metal rich compounds. No discussion of thin films or growth of large crystals. • "Preparation of Thin Films" Joy George This book has a nice succinct treatment of the various thin film deposition methods. • The following references discuss various aspects or methods in solid state synthesis in greater detail. I have listed them according to synthesis method. • Low Temperature & Precursor Techniques • "Crystallization of Solid State Materials via Decomplexation of Soluble Complexes" K.M. Doxsee, Chem. Mater. 10, 2610-2618 (1998). "Accelerating the kinetics of low-temperature inorganic syntheses" R.RoyJ. Solid State Chem. 111, 11-17 (1994). "Nonhydrolytic sol-gel routes to oxides" A. Vioux, Chem. Mater. 9, 2292-2299 (1997). • 3 • Molten Salt Fluxes & Hydrothermal Synthesis • "Turning down the heat: Design and mechanism in solid state synthesis" A. Stein, S. W. Keller, T.E. Mallouk, Science 259, 1558-1563 (1993). • "Synthesis and characterization of a series of quaternary chalcogenides BaLnMQ3 (Ln = rare earth, M = coinage metal, Q = Se or Te)" Y.T. Yang, J.A. Ibers, J. Solid State Chem. 147, 366-371 (1999). • "Hydrothermal Synthesis of Transition metal oxides under mild conditions" M.S. Whittingham, Current opinion in Solid State & Materials Science 1, 227-232 • Chimie Douce & Low Temperature Synthesis "Chimie Douce Approaches to the Synthesis of Metastable Oxide Materials" J. Gopalakrishnan, Chem. Mater. 7, 1265-1275 (1995). • • High Pressure Synthesis "High pressure synthesis of solids" P.F. McMillan, Current Opinion in Solid State & Materials Science 4, 171-178 (1999) "High-Pressure Synthesis of Homologous Series of High Cricitcal Temperature (Tc) Superconductors" E. Takayama-Muromachi, Chem. Mater. 10, 2686-2698 (1998). "Preparative Methods in Solid State Chemistry" J.B. Goodenough, J.A. Kafalas, J.M. Longo, (edited by P. Hagenmuller) Academic Press, New York (1972). 4 Classification of Solids There are several forms solid state materials can adapt Single Crystal Preferred for characterization of structure and properties. Polycrystalline Powder (Highly crystalline) Used for characterization when single crystal cannot be easily obtained, preferred for industrial production and certain applications. Polycrystalline Powder (Large Surface Area) Desirable for further reactivity and certain applications such as catalysis and electrode materials Amorphous (Glass) No long range translational order. Thin Film Widespread use in microelectronics, telecommunications, optical applications, coatings, etc. 5 (1) Area of contact between reacting solids - We want to use starting reagents with large surface area to maximize the contact between reactants Consider the numbers for a 1 cm 3 volume of a reactant • Edge Length = 1 cm # of Crystallites = 1 Surface Area = 6 cm 2 • Edge Length = 10 μm # of Crystallites = 10 9 Surface Area = 6 x 10 3 cm 2 • Edge Length = 100Å # of Crystallites = 10 18 Surface Area = 6 x 10 6 cm 2 - Pelletize to encourage intimate contact between crystallites. Solid State Reactions 6 Time (h) 7 Different parts of the crystal have different structure and different reactivities 8 (2) The rate of diffusion Two ways to increase the rate of diffusion are to • Increase temperature • Introduce defects by starting with reagents that decompose prior to or during reaction, such as carbonates or nitrates. 9 10 (3) The rate of nucleation of the product phase • We can maximize the rate of nucleation by using reactants with crystal structures similar to that of the product (topotactic and epitactic reactions). a topotactic transformation is characterized by internal atomic displacements, which may include loss or gain of material so that the initial and final lattices are in coherence. epitaxy - The growth of the crystals of one mineral on the crystal face of another mineral, such that the crystalline substrates of both minerals have the same structural orientation. [...]... of ions Furthermore, accurate stoichiometric ratios may not always be maintained 18 Molten Salt Fluxes • Solubilize reactants → Enhance diffusion → Reduce reaction temperature • Synthesis in a solvent is the common approach to synthesis of organic and organometallic compounds This approach is not extensively used in solid state syntheses, because many inorganic solids are not soluble in water or organic... and separated from the excess flux by washing with water • Synthesis needs to be carried out at a temperature where the flux is a liquid Purity problems can arise, due to incorporation of the molten salt ions in product This can be overcome either by using a salt containing cations and/or anions which are also present in the desired product (i.e synthesis of Sr2AlTaO6 in a SrCl 2 flux) , or by using salts... SrCl 2 flux) , or by using salts where the ions are of a much different size than the ions in the desired product (i.e synthesis of PbZrO3 in a B2O3 flux) 19 Example 1 • 4SrCO3 + Al2O3 + Ta2O5 àSr2AlTaO6 (SrCl2 flux, 900° C) • Powder sample, wash away SrCl2 with weakly acidic H2O • Direct synthesis requires T > 1400° C and Sr2Ta2O7 impurities persist even at 1600° C 20 21 22 23 Solid State Metathesis Reactions... S The enthalpy of this reaction is ? H = -213 kcal/mol 24 Hydrothermal Synthesis • Reaction takes place in superheated water, in a closed reaction vessel called a hydrothermal bomb (150 < T < 500 ° 100 < P < 3000 kbar) C; • Seed crystals and a temperature gradient can be used for growing crystals • Particularly common approach to synthesis of zeolites • Example : 6CaO + 6SiO 2 à Ca6Si6O 17(OH)2 (150-350... Inert (N2, Ar, etc.) Sulfides – H2S Sealed tube reactions, Vacuum furnaces 7) Grind product and analyze (x-ray powder diffraction) 8) If reaction incomplete, return to step 4 and repeat 13 Example: the synthesis of Sr2CrTaO6 1) Possible starting reagents Sr Metal – Hard to handle, prone to oxidation SrO - Picks up CO 2 & water, mp = 2430 ° C Sr(NO3)2 – mp = 570 ° may pick up some water C, SrCO3 – decomposes... Heat the resulting gel or powder to induce reaction to the desired product The following case studies illustrate some examples of actual syntheses carried out using precursor routes 17 Coprecipitation Synthesis of ZnFe2O4 • Mix the oxalates of zinc and iron together in water in a 1:1 ratio Heat to evaporate off the water As the amount of H2O decreases, a mixed Zn/Fe oxalate (probably hydrated) precipitates... gaseous product (O2), the products are favored by entropy, and the entropy contribution to the free energy become increasingly important as the temperature increases 11 Steps in Conventional Solid State Synthesis 1) Select appropriate starting materials a) Fine grain powders to maximize surface area b) Reactive starting reagents are better than inert c) Well defined compositions 2) Weigh out starting . Hydrothermal Synthesis • "Turning down the heat: Design and mechanism in solid state synthesis& quot; A. Stein, S. W. Keller, T.E. Mallouk, Science 259, 1558-1563 (1993). • " ;Synthesis. Douce Approaches to the Synthesis of Metastable Oxide Materials" J. Gopalakrishnan, Chem. Mater. 7, 1265-1275 (1995). • • High Pressure Synthesis "High pressure synthesis of solids" P.F 1 Solid State Synthesis • Solid State Reactions • Film deposition • Sol-gel method • Crystal Growth 2 • Synthesis References • The material we discussed in