1. CHM 434F/1206F SOLID STATE MATERIALS CHEMISTRY Geoffrey A. Ozin Materials Chemistry Research Group, Chemistry Department, 80 St. George Street, University of Toronto, Toronto, Ontario, Canada M5S 3H6 Tel: 416 978 2082, Fax: 416 971 2011, E-mail: gozin@alchemy.chem.utoronto.cagozin@alchemy.chem.utoronto.ca Group web-page: www.chem.toronto.edu/staff/GAO/group.htmlwww.chem.toronto.edu/staff/GAO/group.html

2. KEY DEVELOPMENTS IN SOLID STATE MATERIALS CHEMISTRY 1. SOLID STATE MATERIALS SYNTHESIS 2. X-RAY DIFFRACTION STRUCTURE OF SOLIDS 3. ELECTRONIC PROPERTIES OF SOLIDS 4. TYPE AND FUNCTION OF DEFECTS IN SOLIDS 5. ENABLED UTILITY OF SOLID STATE MATERIALS IN ADVANCED TECHNOLOGIES

3. PHILOSOPHY OF SOLID STATE MATERIALS SYNTHESIS: CHOOSING A METHOD SOLID STATE SYNTHESIS METHODS ARE DISTINCT TO SOLUTION PHASE PREPARATIVE TECHNIQUES IN THE WAY THAT ONE DEVISES AN APPROACH TO A PARTICULAR PRODUCT THE FORM, SIZE, SHAPE, ORIENTATION, ORGANIZATION AND DIMENSIONALITY AS WELL AS COMPOSITION AND STRUCTURE OF A MATERIAL ARE OFTEN OF PRIME IMPORTANCE ALSO THE STABILITY OF THE MATERIAL UNDER REACTION CONDITIONS (T, P, ATMOSPHERE) IS A KEY CONSIDERATION

4. SIZE AND SHAPE IS EVERYTHING IN THE SOLID STATE MATERIALS WORLD BIG!!!

5. SIZE AND SHAPE IS EVERYTHING IN THE SOLID STATE MATERIALS WORLD SMALL!!!

6. SOLID-STATE MATERIALS CHEMISTRY SYNTHESIS METHODS Direct reactions Precursor methods Crystallization techniques Vapor phase transport - synthesis, purification, crystal growth and doping Ion-exchange methods - solid, solution and melt approaches Injection and intercalation – chemical/electrochemical techniques Chimie Douce - soft-chemistry methods for synthesis of novel meta-stable materials

7. SOLID-STATE MATERIALS CHEMISTRY SYNTHESIS METHODS Sol-gel chemistry, aerogels, xerogels, composites, micro- spheres Nanomaterials synthesis of controlled size, shape, orientation, organization Templated synthesis - zeolites, mesoporous materials, colloidal crystals Electrochemical synthesis – oxidation, reduction and polymerization Thin films and superlattices, chemical, electrochemical, physical Self-assembling monolayers and multilayers, exfoliation- reassembly Single crystal growth - vapor, liquid, solid phase - chemical and electrochemical High-pressure methods, hydrothermal and diamond anvils

8. SOLID-STATE MATERIALS SYNTHESIS Factors influencing solid-state reactions Classes of solid-state synthesis methods Morphology and physical size control of solids Examples of solid state syntheses aimed at designing specific structure-property-function-utility relations into materials

9. SOLID STATE REACTIONS LOOK DECEPTIVELY SIMPLE - DO NOT BE FOOLED! GRAPHITE SEMIMETAL FIRST STAGE SECOND STAGE THIRD STAGE RT METALS AND LOW T SUPERCONDUCTORS CnKCnK K(g) Intercalation of potassium into graphite - graphite as an electron acceptor

10. K(g) K(ads) K + (ads) e-e- e-e- Surface adsorption - wax layer stops entire process Electron transfer from K to  * empty band of G Interlayer expansion of G layers Ion - electron injection into layer space and band K+K+ GETTING BETWEEN THE SHEETS?

11. COMPLICATIONS BETWEEN THE SHEETS? Mixed staging Elastic deformation around K + Quadrupolar interactions induce intralayer K + ordering Bending of G layers

12. SEEING THE MIXED STAGE C-FeCl 2 BY TEM

13. SEEING ELASTICALLY DEFORMABLE INTERCALATED GRAPHITE LAYERS BY TEM

14. INTERCALATION- CHEMISTRY BETWEEN THE SHEETS - A NICE EXAMPLE OF THE COMPLEXITY OF A SIMPLE SOLID-VAPOR REACTION Chemical, electrochemical syntheses Intercalation thermodynamics Intercalation kinetics Mechanism of intercalation - entry, nucleation, growth Ion-electron transport Polytypism - layer registry Staging structural details - guest distribution Layer bending - elastic deformation Extent of charge transfer from guest to host Metal-superconductor transition

15. HOW AND WHY DO SOLIDS REACT? Reactivity of solids Fundamental aspect of solid state chemistry Chemical reactivity of solid state materials depends on form and physical dimensions as well as structure and imperfections of reactants and products Factors governing solid state reactivity underpin concepts and methods for the synthesis of new solid state materials Solid state synthesis, making materials with desired size and shape, structure and properties, function and utility, is distinct to liquid and gas phase homogeneous reactions

16. HOW AND WHY DO SOLIDS REACT? Liquid and gas phase reactions Driven by intrinsic reactivity (chemical potential, activation energy) and concentration of chemical species Contrast solid phase reactions Controlled by arrangement of chemical constituents in crystal and imperfections rather than intrinsic reactivity of constituents Solid state reactivity Also determined by particle size and shape, surface area, grain packing, crystallographic plane, adsorption effects, temperature, pressure, atmosphere

17. CLASSIFYING SOLID STATE REACTIONS Solid  products Decompositions, polymerizations (topochemical), phase change - growth of product within reactant MoO 3.2H 2 O  MoO 3.H 2 O  MoO 3 topotactic dehydration - water loss - layer structure maintained Avrami kinetics - sigmoid curves - mechanism- reactions involving a single solid phase - induction-nucleation, growth product, depletion of reactant

18. Unique 2-D layered structure of MoO 3 Chains of corner sharing octahedral building blocks sharing edges with two similar chains, Creates corrugated MoO 3 layers, stacked to create interlayer VDW space, Three crystallographically distinct oxygen sites, sheet stoichiometry 3x1/3 ( ) +2x1/2 ( )+1 ( ) = 3O

19.  = m(t)/m(  ) = 1 - exp[k(t-  )] n SOLID TO SOLID TRANSFORMATIONS Nucleation and growth of one solid phase within another described by Avrami type kinetics - random and isolated nucleation with 1-D, 2-D or 3-D growth - reconstructive and displacive mechanisms  = fraction of reaction completed, k = rate constant,  = incubation time for nucleation, n = dimensionality dependent exponent t  = m(t)/m(  ) Incubation  Growth Depletion

20. CLASSIFYING SOLID STATE REACTIONS Solid + gas  products Oxidation, reduction, nitridation, intercalation dx/dt = k/x parabolic growth kinetics Rate limiting diffusion of reactants through product layer growing on solid reactant phase

21. CLASSIFYING SOLID STATE REACTIONS Solid + solid  products Additions, metathesis/exchange, complex processes ZnO + Fe 2 O 3  ZnFe 2 O 4 ZnS + CdO  CdS + ZnO Solid state interface reactions - depends on contact area, mass transport of reactants through product layer, nucleation and growth of product phase dx/dt = k/x parabolic growth kinetics

22. CLASSIFYING SOLID STATE REACTIONS Solid + liquid/melt  products Dissolution, corrosion, electro-deposition, intercalation, ion-exchange, acid leaching Classic case of Grignard formation Mg(s) + RX(l) + Et 2 O(l)  RMgX.2Et 2 O Classic case of LiAlO 2  HAlO 2 exchange of Li + for H + in between AlO 2 layers of a NaCl rock salt type structure Reactivity of exposed crystallographic planes, surface defects and adsorption

23. CLASSIFYING SOLID STATE REACTIONS Surface + reactant  product Tarnishing (Ag/H 2 S), passivation (Al/O 2 ), heterogeneous catalysis (Pt/H 2 /C 6 H 6 ) Key surface species and reactivity, surface structure and composition, adsorption-dissociation-diffusion- reaction

24. Classical exchange or metathesis reactions Look very simple, in practice actually extremely complicated Consider zinc blende type reagents with dominant cation mobility CdS + ZnO  CdO + ZnS REACTIVITY OF SOLIDS - SUPERFICIALLY SIMPLE, INTRINSICALLY COMPLEX

25. Two limiting mechanisms Reactants and products both crystallographically related, zinc blende type lattice Assume cation mobility dominates through product layers A) Cations diffuse through adjacent product coherent layers B) Cations diffuse through product mosaic layers REACTIVITY OF SOLIDS - SUPERFICIALLY SIMPLE, INTRINSICALLY COMPLEX

26. Metal exchange reactions also very complicated Ion and electron migration across product interface Cu + AgCl  CuCl + Ag 2Cu + Ag 2 S  Cu 2 S + 2Ag Ionic and electronic mobility required REACTIVITY OF SOLIDS - SUPERFICIALLY SIMPLE, INTRINSICALLY COMPLEX

27. THINKING ABOUT MATERIALS SYNTHESIS Solid state materials chemistry concerns the chemical and physical properties of solids with structures based upon infinite lattices or extended networks of interconnected atoms, ions, molecules or complexes in 1-D, 2-D or 3-D NOT THE CHEMISTRY OF MOLECULAR SOLIDS Different techniques and concepts for synthesis and characterization of solid state materials from those conventionally applied to molecular solids, liquids, liquid crystals, solutions and gases VARIOUS CLASSES OF SOLID STATE SYNTHESIS

28. SHAPE, SIZE AND DEFECTS ARE EVERYTHING! Form or morphology and physical size of product controls synthesis method of choice and potential utility Single crystal, phase pure, defect free solids - do not exist and if they did not likely of much interest! Single crystal (SC) that has been defect modified with dopants - intrinsic vs extrinsic, non- stoichiometry - is the way to control the chemical and physical properties, function and utility SC preferred for structure and properties characterization

29. SHAPE IS EVERYTHING! Microcrystalline powder Used for characterization when single crystal can not be easily obtained, preferred for industrial production and certain applications, useful for control of reactivity, catalytic chemistry, electrode materials Polycrystalline pellet, tube, rod, wire Super-conducting ceramic wires, magnets Single crystal or polycrystalline film Widespread use in microelectronics, telecommunications, optical applications, coatings, etc. Epitaxial film - superlattice films - lattice matching, tolerance factor, elastic strain, defects Important for electronic, optical, magnetic device construction Non-crystalline, amorphous, glassy - fibers, films, tubes, plates No long range translational order - control mechanical, optical-electronic- magnetic properties Nanocrystalline - dimensions where properties scale with size Quantum size effect materials and devices - discrete electronic rather than continuous electronic bands

30. FACTORS INFLUENCING REACTIONS OF SOLIDS Reaction conditions - temperature, pressure, atmosphere Structural considerations Reaction mechanism Surface area of precursors Defect concentration and defect type

31. FACTORS INFLUENCING REACTIONS OF SOLIDS Nucleation of one phase within another Diffusion rates of atoms, ions, molecules in solids Epitactic and topotactic reactions Surface structure and reactivity of different crystal planes

32. ARCHETYPE DIRECT SOLID STATE REACTION Model reaction MgO + Al 2 O 3  MgAl 2 O 4 (Spinel ccp O 2-, Mg 2+ 1/8 Td, Al 3+ 1/2 Oh) MgOAl 2 O 3 MgOAl 2 O 3 Mg 2+ Al 3+ Single crystals of MgO, Al 2 O 3 Original interface MgAl 2 O 4 /Al 2 O 3 new reactant/product interface MgAl 2 O 4 /MgO new reactant/product interface MgAl 2 O 4 /MgO new product layer thickness x x/4 3x/4 Thermodynamic and kinetic factors at work in formation of product spinel from solid state precursors t = 0 t = t

33. ARCHETYPE DIRECT SOLID STATE REACTION Thermodynamic and kinetic factors need to be understood Model reaction MgO Rock Salt + Al 2 O 3 Corundum  MgAl 2 O 4 Spinel (ccp O 2-, Mg 2+ 1/8 Td, Al 3+ 1/2 Oh) Single crystals of precursors, interfaces between reactants, temperature T On reaction, new reactant-product MgO/MgAl 2 O 4 and Al 2 O 3 /MgAl 2 O 4 interfaces form Free energy of spinel formation negative, favors reaction Extremely slow at normal temperatures - complete reaction can take several days at 1500 o C

34. ROCK SALT CRYSTAL STRUCTURE OM x y

35.  -Al 2 O 3 CORUNDUM CRYSTAL STRUCTURE BLOCK REPRESENTATION hcp O 2- Al 3+ 2/3 Oh sites

36. SPINEL CRYSTAL STRUCTURE ccp O 2-, Mg 2+ 1/8 Td, Al 3+ 1/2 Oh

37. ARCHETYPE DIRECT SOLID STATE REACTION Interfacial growth rates 3 : 1 Linear dependence of interface thickness x 2 versus t Why is nucleation, mass transport so difficult? MgO ccp O 2-, Mg 2+ in Oh sites Rock Salt Al 2 O 3 hcp O 2-, Al 3+ in 2/3 Oh sites Corundum MgAl 2 O 4 ccp O 2-, Mg 2+ 1/8 Td, Al 3+ 1/2 Oh Spinel

38. ARCHETYPE DIRECT SOLID STATE REACTION Structural differences between reactants and products Major structural reorganization in forming product spinel Making and breaking strong bonds (mainly ionic) Long range counter-diffusion of Mg(2+) and Al(3+) cations across interface, usually RDS Requires ionic conductivity - substitutional (S) or interstitial (F) hopping of cations from site to site - effects mass transport High temperature process as D(Mg2+) and D(Al3+) small for small highly charged cations

39. ARCHETYPE DIRECT SOLID STATE REACTION Nucleation of product spinel at interface, ions diffuse across thickening interface Oxide ion reorganization at nucleation site Decreasing rate as spinel product layer x thickens Planar Layer Model - Parabolic rate law: dx/dt = k/x x 2 = kt

40. ARCHETYPE DIRECT SOLID STATE REACTION Easily monitored with colored product at interface, T and t NiO + Al 2 O 3  NiAl 2 O 4 Linear x 2 vs t plots observed Arrhenius equation temperature dependence of the reaction rate constant k= Aexp(-Ea/RT) lnk vs 1/T experiments provides Arrhenius activation energy Ea for the solid state reaction