Transcript CHM 434F/1206F SOLID STATE MATERIALS CHEMISTRY

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
BIG!!!
SIZE AND SHAPE IS EVERYTHING IN THE SOLID
STATE MATERIALS WORLD
SMALL!!!
SIZE AND SHAPE IS EVERYTHING IN THE SOLID
STATE MATERIALS WORLD
SOLID-STATE MATERIALS CHEMISTRY SYNTHESIS
METHODS
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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, microspheres
• 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, exfoliationreassembly
• Single crystal growth - vapor, liquid, solid phase chemical and electrochemical
• High-pressure methods, hydrothermal and diamond
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!
Intercalation of potassium into graphite - graphite as an electron acceptor
CnK
K(g)
GRAPHITE
SEMIMETAL
FIRST STAGE SECOND STAGE THIRD STAGE
RT METALS AND LOW T SUPERCONDUCTORS
K(g)
K(ads)
GETTING BETWEEN THE SHEETS?
e-
e-
K+(ads)
K+
• Surface adsorption - wax layer stops entire process
• Electron transfer from K to p* empty band of G
• Interlayer expansion of G layers
• Ion - electron injection into layer space and band
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
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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,
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 - mechanismreactions 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
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
a = fraction of reaction completed, k = rate constant, t = incubation time for nucleation,
n = dimensionality dependent exponent
a = m(t)/m() = 1 - exp[k(t-t)]n
a = m(t)/m()
Depletion
Incubation t
Growth
t
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
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-diffusionreaction
REACTIVITY OF SOLIDS - SUPERFICIALLY
SIMPLE, INTRINSICALLY COMPLEX
• 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
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, nonstoichiometry - is the way to control the chemical
and physical properties, function and utility
• SC preferred for structure and properties
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-electronicmagnetic properties
• Nanocrystalline - dimensions where properties scale
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)
Mg2+
t=0
MgO
Thermodynamic and
kinetic factors at work
in formation of product
spinel from solid state
precursors
Single crystals of
MgO, Al2O3
Al2O3
Original interface
Al3+
MgAl2O4/Al2O3 new
reactant/product
interface
MgO
t=t
Al2O3
MgAl2O4/MgO new
reactant/product
interface
x/4
3x/4
MgAl2O4/MgO new
product layer
thickness x
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
ROCK SALT CRYSTAL STRUCTURE
M
O
y
x
Al3+ 2/3 Oh sites
hcp O2-
a-Al2O3
CORUNDUM
CRYSTAL
STRUCTURE
BLOCK
REPRESENTATION
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