CHM 434F/1206F SOLID STATE MATERIALS CHEMISTRY Geoffrey A. Ozin Materials Chemistry Research Group, Chemistry Department, 80 St. George Street, University.

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: [email protected]

Group web-page: www.chem.toronto.edu/staff/GAO/group.html

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

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

SIZE AND SHAPE IS EVERYTHING IN THE SOLID STATE MATERIALS WORLD

BIG!!!

SIZE AND SHAPE IS EVERYTHING IN THE SOLID STATE MATERIALS WORLD

SMALL!!!

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

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

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

SOLID STATE REACTIONS LOOK DECEPTIVELY SIMPLE - DO NOT BE FOOLED!

GRAPHITE SEMIMETAL

FIRST STAGE SECOND STAGE THIRD STAGERT METALS AND LOW T SUPERCONDUCTORS

CnK

K(g)

Intercalation of potassium into graphite - graphite as an electron acceptor

K(g)

K(ads) K+(ads)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+

GETTING BETWEEN THE SHEETS?

COMPLICATIONS BETWEEN THE SHEETS?

• Mixed staging

• Elastic deformation around K+

• Quadrupolar interactions induce intralayer K+ ordering

• Bending of G layers

SEEING THE MIXED STAGE C-FeCl2 BY TEM

SEEING ELASTICALLY DEFORMABLE

INTERCALATED GRAPHITE

LAYERS BY TEM

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

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

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

CLASSIFYING SOLID STATE REACTIONS

• Solid products

• Decompositions, polymerizations (topochemical), phase change - growth of product within reactant

• MoO3.2H2O MoO3.H2O MoO3 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

Unique 2-D layered structure of MoO3

Chains of corner sharing octahedral building blocks sharing edges with two similar chains,

Creates corrugated MoO3 layers, stacked to create interlayer VDW space,

Three crystallographically distinct oxygen sites, sheet stoichiometry 3x1/3 ( ) +2x1/2 ( )+1 ( ) = 3O

= 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

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

CLASSIFYING SOLID STATE REACTIONS

• Solid + solid products

• Additions, metathesis/exchange, complex processes

• ZnO + Fe2O3 ZnFe2O4

• 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

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) + Et2O(l) RMgX.2Et2O

• Classic case of LiAlO2 HAlO2 exchange of Li+ for H+ in between AlO2 layers of a NaCl rock salt type structure

• Reactivity of exposed crystallographic planes, surface defects and adsorption

CLASSIFYING SOLID STATE REACTIONS

• Surface + reactant product

• Tarnishing (Ag/H2S), passivation (Al/O2), heterogeneous catalysis (Pt/H2/C6H6)

• Key surface species and reactivity, surface structure and composition, adsorption-dissociation-diffusion- reaction

• 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

• 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

• Metal exchange reactions also very complicated

• Ion and electron migration across product interface

• Cu + AgCl CuCl + Ag

• 2Cu + Ag2S Cu2S + 2Ag

• Ionic and electronic mobility required

REACTIVITY OF SOLIDS - SUPERFICIALLY SIMPLE, INTRINSICALLY COMPLEX

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

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

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

FACTORS INFLUENCING REACTIONS OF SOLIDS

• Reaction conditions - temperature, pressure, atmosphere

• Structural considerations

• Reaction mechanism

• Surface area of precursors

• Defect concentration and defect type

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

ARCHETYPE DIRECT SOLID STATE REACTION

Model reaction MgO + Al2O3 MgAl2O4 (Spinel ccp O2-, Mg2+ 1/8 Td, Al3+ 1/2 Oh)

MgO Al2O3

MgO Al2O3

Mg2+

Al3+

Single crystals of MgO, Al2O3

Original interface

MgAl2O4/Al2O3 new reactant/product interface

MgAl2O4/MgO new reactant/product interface

MgAl2O4/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

ARCHETYPE DIRECT SOLID STATE REACTION

• Thermodynamic and kinetic factors need to be understood

• Model reaction MgO Rock Salt + Al2O3 Corundum MgAl2O4 Spinel (ccp O2-, Mg2+ 1/8 Td, Al3+ 1/2 Oh)

• Single crystals of precursors, interfaces between reactants, temperature T

• On reaction, new reactant-product MgO/MgAl2O4 and Al2O3/MgAl2O4 interfaces form

• Free energy of spinel formation negative, favors reaction

• Extremely slow at normal temperatures - complete reaction can take several days at 1500oC

ROCK SALT CRYSTAL STRUCTURE

OO

MM

x

y

-Al2O3

CORUNDUM CRYSTAL

STRUCTURE

BLOCK REPRESENTATION

hcp O2-

Al3+ 2/3 Oh sites

SPINEL CRYSTAL STRUCTURE ccp O2-, Mg2+ 1/8 Td, Al3+ 1/2 Oh

ARCHETYPE DIRECT SOLID STATE REACTION

• Interfacial growth rates 3 : 1

• Linear dependence of interface thickness x2 versus t

• Why is nucleation, mass transport so difficult?

• MgO ccp O2-, Mg2+ in Oh sites Rock Salt

• Al2O3 hcp O2-, Al3+ in 2/3 Oh sites Corundum

• MgAl2O4 ccp O2-, Mg2+ 1/8 Td, Al3+ 1/2 Oh Spinel

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

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

• x2 = kt

ARCHETYPE DIRECT SOLID STATE REACTION

• Easily monitored with colored product at interface, T and t

• NiO + Al2O3 NiAl2O4

• Linear x2 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