CHM 434F/1206F 2009

SOLID STATE MATERIALS CHEMISTRY

Geoffrey A. Ozin

Materials Chemistry and Nanochemistry 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@chem.utoronto.ca

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

Password: GoMaterials

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

THE “HEART” OF MATERIALSHOW DOES ONE THINK ABOUT THE CHEMICAL SYNTHESIS, MODE OF FORMATION AND

REACTIVITY OF NEW AND EXISITING MATERIALS WHICH TARGET SPECIFIC RELATIONS BETWEEN STRUCTURE, PROPERTY, FUNCTION AND UTILITY?

• BaY2Cu3O7-x - defect Perovskite - x control of Cu oxidation states (II,III) - superconductor, metal, semiconductor properties - high Tc superconductor - magnetic levitation trains – magnetic detector/SQUIDS

• SrxLa1-xMnO3 defect Perovskite - x control of Mn (III, IV) oxidation states electronic and oxide ion conductivity – cathode - solid oxide fuel cell

• LixCo1-y-zNiyMnzO2 – layered cobalt oxide – VDW gap – lithium intercalation electron injection – structure command of material volume swings on cycling, y, z control of electronic and lithium ion conductivity and x lithium capacity – cathode – lithium solid state battery

PHILOSOPHY OF SOLID STATE MATERIALS SYNTHESIS: CHOOSING A METHOD

• SOLID STATE MATERIALS SYNTHESIS METHODS ARE DISTINCT TO SOLUTION PHASE PREPARATIVE TECHNIQUES IN THE WAY THAT ONE DEVISES AN APPROACH TO A PARTICULAR PRODUCT AND THE WAY ONE CHOOSES PRECURSORS AND HOW THEY REACT IN THE SOLID STATE AND NUCLEATE AND GROW

• THE FORM , SIZE, SHAPE, ORIENTATION, ORGANIZATION AND DIMENSIONALITY AS WELL AS BULK AND SURFACE 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!!!

PIEZOELECTRIC QUARTZ CRYSTAL OSCILLATORS IN NANO MASS

BALANCES AND WATCHES

SIZE AND SHAPE AND SURFACE IS EVERYTHING IN THE SOLID STATE NANOMATERIALS WORLD

SMALL!!!SUPERPARAMAGNETIC

MnNi2O4 SPINEL CONTRAST AGENT IN MRI

SMALL!

SIZE AND SHAPE AND SURFACE IS EVERYTHING IN THE SOLID STATE NANOMATERIALS WORLD

MgB2 SUPERCONDUCTING HELICAL FLEXIBLE

NANOCABLES!

SOLID-STATE MATERIALS SYNTHESIS

• Factors influencing solid-state reactions

• Classes of solid-state synthesis methods

• Size, shape and surface control of solids

• Examples of solid state syntheses – choosing precursors – choosing a method - 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- transfere-

• Surface adsorption - wax top layer stops entire process!!!

• Electron transfer from K to * empty band of G

• Electron repulsion driven interlayer expansion of G layers

• Higher mobility of smaller K+ compared to K0

• Facilitates K+ ion injection into layer space

K+

GETTING BETWEEN THE SHEETS?

K+ migration - insertion

e- repulsion between sheets

COMPLICATIONS BETWEEN THE SHEETS?

• Mixed staging – may not be what you think!!!

• Defects and bending of G layers

• Elastic deformation around intralayer K+

• Quadrupolar interactions induce intralayer K+ ordering

SEEING THE MIXED STAGE C-FeCl2 BY TEM

SEEING ELASTICALLY DEFORMABLE

INTERCALATED GRAPHITE

LAYERS AND GRAPHITE

DEFECT LAYERS BY

TEM

INTERCALATION - CHEMISTRY BETWEEN THE SHEETS - A NICE EXAMPLE OF THE COMPLEXITY AND

ELEGANCE OF A SIMPLE SOLID-VAPOR REACTION

• Chemistry – electrochemistry – synthetic method

• Intercalation thermodynamics - energetics

• Intercalation kinetics – rate – chemical or diffusion control

• Mechanism of intercalation - entry, nucleation, growth

• Ion-electron transport mechanism - mobility

• Polytypism - layer registry

• Staging structural details - guest distribution

• Layer bending - elastic deformation – defects

• Extent of charge transfer from guest to host - electronics

• Metal-superconductor transition – temperature effect

HOW AND WHY DO SOLIDS REACT?

• Thinking about the reactivity of solids

• Fundamental aspect of solid state chemistry

• Chemical reactivity of solid state materials depends on form and physical dimensions as well as bulk and surface 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, bulk and surface composition and desired relation between structure, properties, function and utility, is distinct to liquid and gas phase homogeneous reactions

HOW AND WHY DO SOLIDS REACT?

• Think about conventional liquid and gas phase reactions • Driven by intrinsic reactivity (chemical potential,

activation energy), temperature and concentration of chemical species

• Contrast solid phase reactions• Controlled by arrangement of chemical constituents in

bulk and surface of crystal and crystal imperfections and surface and bulk diffusion rather than intrinsic reactivity of constituents

• Solid state reactivity• Also determined by particle size and shape, surface area,

grain packing, surface crystallographic plane, adsorption effects, temperature, pressure, atmosphere

CLASSIFYING SOLID STATE REACTIONS

• Solid Solid Product

• Decompositions, polymerizations (topochemical), phase transition - 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 of product, depletion of reactant

Unique 2-D layered structure of MoO3 with water hydrogen bonded to and located between the sheets

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 at high

energy defect sites with 1-D, 2-D or 3-D growth - reconstructive and displacive mechanisms

= fraction of reaction completed, k = rate constant for product formation, =

incubation time for nucleation, n = dimensionality dependent exponent

t

= m(t)/m()

Incubation Growth

Depletion

CLASSIFYING SOLID STATE REACTIONS

• Solid + Gas Solid Product

• Oxidation, reduction, nitridation, intercalation

• dx/dt = k/x parabolic growth kinetics of layer of product

• Rate limiting diffusion of reactants through product layer growing on solid reactant phase – inverse relation to the thickness of the product layer

Gas

Solid

CLASSIFYING SOLID STATE REACTIONS

• Surface + Gaseous Reactant Solid Product

• Tarnishing (Ag/H2SAg2S), passivation (Al/O2Al2O3), chemical vapor deposition (GaAs/Me3In/PH3GaAs-InP)

• Key surface species and surface reactivity: surface structure, surface composition, surface defects, adsorption-desorption-dissociation-diffusion processes - reaction

CLASSIFYING SOLID STATE REACTIONS

• Solid + Solid Solid Products

• Additions, metathesis/exchange, alloying are complex processes

• ZnO + Fe2O3 ZnFe2O4

• ZnS + CdO CdS + ZnO

• ZnSe + CdSe ZnxCd1-xSe

• Solid state interfacial reactions - depends on contact area, diffusive mass transport of reactants through product layer, nucleation and growth of product phase

• dx/dt = k/x parabolic growth kinetics

• CdS + ZnO CdO + ZnS

• Classical ion exchange or metathesis reactions

• Look very simple on paper but in practice actually extremely complicated

• Consider contact of zinc blende type reagents with dominant cation mobility (size, charge, Schottky/Frenkel substitutional/interstitial cation diffusion ideas)

REACTIVITY OF SOLIDS - SUPERFICIALLY SIMPLE, INTRINSICALLY COMPLEX

• CdS + ZnO CdO + ZnS

• Two products two limiting mechanisms

• Reactants and products both crystallographically related, zinc blende type lattice - fcc anions - cations in half Td sites

• Assume cation mobility dominates through product layers

• A) Cations diffuse through adjacent product coherent layer

• B) Cations diffuse through product mosaic layer - distribution of CdO/ZnS in product layer

REACTIVITY OF SOLIDS - SUPERFICIALLY SIMPLE, INTRINSICALLY COMPLEX

• Metal exchange reactions also very complicated

• Ion migration and electron interchange across product interface

• Cu + AgCl CuCl + Ag

• 2Cu + Ag2S Cu2S + 2Ag

• Cu/Ag ionic and electronic mobility in AgCl/CuCl required to enable reaction – coherent CuCl/Ag or distribution of CuCl/Ag in product layer

REACTIVITY OF SOLIDS - SUPERFICIALLY SIMPLE, INTRINSICALLY COMPLEX

CLASSIFYING SOLID STATE REACTIONS

• Solid + Liquid/Melt Solid Products

• Dissolution, corrosion, anodization, electrodeposition, intercalation, ion-exchange

• Classic case of Grignard formation

Mg(s) + RX(l) + Et2O(l) RMgX.2Et2O

oxidative addition of R-X across surface Mg(0) to give RMg(II)X with formation of Mg(II)-OEt2 coordinate bond

• Classic case of

LiAlO2 HAlO2

Li+ for H+ ion exchange between AlO2 layers of rock salt type structure

• Reactivity of exposed crystallographic planes

• Surface defects, adsorption, dissociation, de-sorption, diffusion, reaction

GRIGNARD FORMATION – SIMPLE ON PAPER COMPLEX IN PRACTICE!!!

Mg Mg Mg(0) Mg Mg(II) Mg Mg Mg Mg Mg Mg Mg Mg Mg Mg Mg Mg Mg

R-Cl

R••Cl

Et2O

R Cl

R Cl

Mg

Et2O OEt2

RCl surface adsorption, RCl oxidative-addition, Mg-Mg bond breaking, Et2OMg coordination, Grignard surface desorption (Et2O)2RMgCl

WHEN THINKING ABOUT MATERIALS SYNTHESIS

• WHAT IS SOLID STATE MATERIALS CHEMISTRY?WHAT IS SOLID STATE MATERIALS CHEMISTRY? the synthesis, chemical and physical properties, function

and utility of solids with structures based upon infinite lattices or extended networks of interconnectedinterconnected atoms, ions, molecules, complexes or clusters in 1-D, 2-D or 3-D spatial dimensions

• NOT THE CHEMISTRY OF MOLECULES OR NOT THE CHEMISTRY OF MOLECULES OR MOLECULAR SOLIDSMOLECULAR SOLIDS

• Different techniques and concepts for synthesis, characterization and properties measurements of solid state materials from those conventionally applied to molecular solids, liquids, liquid crystals, solutions and gases

• VARIOUS CLASSES OF SOLID STATE SYNTHESESVARIOUS CLASSES OF SOLID STATE SYNTHESES

PORTFOLIO OF SOLID-STATE MATERIALS CHEMISTRY SYNTHESIS METHODS

• Direct reactions of solids • Precursor methods – single and multiple element source • Co-crystallization techniques • Vapor phase transport – synthesis as well as

purification, crystal growth and doping • Ion-exchange methods - solid, solution and melt

approaches• Injection and intercalation – chemical/electrochemical

techniques• Chimie Douce – bringing down the heat soft-chemistry

methods for synthesis of novel meta-stable materials

PORTFOLIO OF SOLID-STATE MATERIALS CHEMISTRY SYNTHESIS METHODS

• Sol-gel chemistry, aerogels, xerogels, organic-inorganic composites, microspheres, films

• Nanomaterials synthesis of controlled size, shape, orientation, surface and bulk structure and composition plus organization

• Templated synthesis - zeolites, mesoporous materials, colloidal crystals

• Electrochemical synthesis – oxidation, reduction and polymerization, anodic oxidation nanochannel membranes

• Thin films and superlattices, chemical, electrochemical, physical• Self-assembled monolayers and multilayers, exfoliation-

reassembly of layered solids • Single crystal growth - vapor, liquid, solid phase - chemical and

electrochemical• High-pressure synthesis - hydrothermal and diamond anvils

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 new product layer thickness x

x/4

3x/4

Thermodynamic and kinetic factors at work in formation of product Spinel from solid state precursors at T

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 crystal precursors, interfaces between reactants, reaction temperature T

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

• Free energy of Spinel formation negativenegative, favors reaction

• High Ea - extremely slow reaction at normal temperatures - complete reaction can take several days even at 1500oC

FACTORS INFLUENCING REACTIONS OF SOLIDS

• Reaction conditions - temperature, pressure, atmosphere

• Structural considerations – precursors and products

• 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, clusters in solids

• Epitactic surface and topotactic bulk reactions with lattice matching criteria to minimize elastic strain

• Surface structure and reactivity of different crystal planes

MO - ROCK SALT STRUCTURE – 2 INTERPENETRATING FCC LATTICES – FCC LATTICE OF O WITH M IN EVERY OCTAHEDRAL SITE - CUBIC ARRAY OF

CORNER AND EDGE SHARING OCTAHEDRAL BUILDING BLOCKS – BLOCK REPRESENATION - 6 COORDINATE M CATIONS AND O ANIONS

OO

MM

x

y

-Al2O3

CORUNDUM CRYSTAL

STRUCTURE

Oh BLOCK REPRESENTATION

ABAB…

hcp O2-

Al3+ 2/3 Oh sites

SPINEL CRYSTAL STRUCTURE – BLOCK REPRESENTATION

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

ARCHETYPE DIRECT SOLID STATE REACTION

• QUESTIONS TO ASK

• Interfacial linear 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

Why is nucleation, mass transport so difficult ???

• 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 small, highly charged, highly polarizing Mg(2+) and Al(3+) cations through polarizable lattice of larger O(2-) and across growing interface, usually RDS

• Requires ionic conductivity - substitutional (S) or interstitial (F) hopping of cations from site to site - controls mass transport

• High T/Ea process as diffusion constants D(Mg2+) and D(Al3+) are small for small, highly charged, highly polarizing cations

KINETICS OF DIRECT SOLID STATE REACTION

• Nucleation of product Spinel at interface, ions diffuse across thickening Spinel 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

KINETICS OF DIRECT SOLID STATE REACTION

• Easily monitored with differently colored product at interface

• Watch colored boundary move as a function of T and t

• NiO + Al2O3 NiAl2O4

• Linear x2 vs t plots observed provides rate constant k

• 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

CHARGE BALANCE IN SOLID STATE INTERFACIAL REACTIONS

• 3Mg(2+) diffuse in opposite way to 2Al(3+)

• MgO/MgAlMgO/MgAl22OO44 Interface LHS Interface LHS

• 2Al(3+) - 3Mg(2+) + 4MgO 1MgAl2O4 LHS

• MgAlMgAl22OO44/Al/Al22OO3 3 Interface RHSInterface RHS

• 3Mg(2+) - 2Al(3+) + 4Al2O3 3MgAl2O4 RHS

• Overall Reaction

• 4MgO + 4Al2O3 4MgAl2O4

• RHS/LHS growth rate of interface = 3/1 Kirkendall Effect

KIRKENDALL EFFECT

OTHER SOLID STATE REACTIONS

• MgO + Fe2O3 MgFe2O4

• Different color interfaces

• Easily monitored rates

• Other examples - calculate the Kirkendall ratio:

• SrO + TiO2 SrTiO3 Perovskite, AMO3 (type ReO3)

• 2KF + NiF2 K2NiF4 Corner Sharing Oh NiF6(2-) Sheets, Inter-sheet K(+)

• 2SiO2 + Li2O Li2Si2O5

ROCK SALT CRYSTAL STRUCTURE

OO

MM

x

y

RUTILE CRYSTAL STRUCTURE

x

y

z

PEROVSKITE CRYSTAL STRUCTURE

AA

OO

MM

PEROVSKITE CAMELEON

DEFECTS AND NON-STOICHIOMETRY CONTROL STRUCTURE-PROPERTY-FUNCTION-UTILITY RELATIONS

• LiNbO3 non-linear optical ferroelectric - E-field RI control - electrooptical switch

• SrTiO3 dye sensitized semiconductor liquid junction photocathode - solar cell

• HxWO3 proton conductor - hydrogen/oxygen fuel cell electrolyte

• BaY2Cu3O7 high Tc superconductor - magnetic levitation trains - detector/SQUIDS

• BaTiO3 ferroelectric high dielectric capacitor, photorefractive – holography

• CaxLa1-xMnO3 x control F-metal to P-semiconductor – spin control of resistance - GMR - data storage

• SrxLa1-xMnO3 x control e-/oxide ion conductor - solid oxide fuel cell cathode

• PbZrxTi1-xO3 piezoelectric - oscillator, nano-positioning

K2NiF4 Corner Sharing Oh NiF6(2-) Sheets, Inter-sheet K(+)

NiF2

KF

KF

NiF2

KF

KF

NiF2

SHAPE, SIZE AND DEFECTS ARE EVERYTHING!

• Form, habit, morphology and physical size of product controls synthesis method of choice, rate and extent of reaction and reactivity

• 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 - controls chemical and physical properties, function, utility

• SC preferred over microcrystalline powders for structure and properties characterization and nanocrystals have distinct properties

SHAPE IS EVERYTHING!• Microcrystalline powder Used for characterization when single crystal can not be

easily obtained, preferred for industrial production and certain applications, where large surface area useful like control of reactivity, catalytic chemistry, separation materials, energy materials

• Polycrystalline shapes like pellet, tube, rod, wire Super-conducting ceramic wires, ceramic engines, aeronautical parts, magnets

• Single crystal or polycrystalline film Widespread use in microelectronics, optical telecommunications, photonic applications, coatings – protective, antireflection, self-cleaning

• Epitaxial film – multilayer superlattice films - lattice matching, tolerance factor, elastic strain, defects important for fabrication of electronic, magnetic, optical planarized devices

• Non-crystalline, amorphous, glassy - fibers, films, tubes, plates No long range translational order – just short range local order - control mechanical, optical-electrical-magnetic properties like fiber optic cables, fiber lasers, optical components

• Nanocrystalline – below a certain dimensions properties scale with size Quantum size effect materials – electronic, optical, magnetic devices - discrete electronic energy levels rather than continuous electronic bands – also useful in nanomedicine like drug delivery, imaging contrast agents, cancer therapy, and fuel, battery, solar cell materials