TOPOTACTIC SOLID-STATE SYNTHESIS

METHODS: HOST-GUEST INCLUSION CHEMISTRY

• Ion-exchange, injection, intercalation type synthesis

• Ways of modifying existing solid state structures while maintaining the integrity of the overall structure

• Precursor structure

• Open structure or porous framework

• Ready diffusion of guest atoms, ions, organic molecules, polymers, organometallics, coordination compounds, nanoclusters, bio(macro)molecules into and out of the structure of nanoporous crystals

TOPOTAXY: HOST-GUEST INCLUSION

1D- Tunnel Structures

TiO2 hWO3 TiS3

2D- Layered Structures

Graphite

TiS2 TiO2(B) KxMnO2 FeOCl

HxMoO3

b aluminaLixCoO2

3D-Frameworks

zeolites

MOFs

LiMn2O4 cWO3

Pivotal topotactic materials and

their properties for functional

utility in Li solid state battery

electrodes, electrochromic

mirrors, windows and displays,

fuel and solar cell electrolytes and

electrodes, chemical sensors,

superconductors, gas storage

TOPOTACTIC SOLID-STATE SYNTHESIS

METHODS: HOST-GUEST INCLUSION CHEMISTRY

• Penetration into interlamellar spaces: 2-D intercalation

• Into 1-D channel voids: 1-D injection

• Into cavity spaces: 3-D injection

• Classic materials for this kind of topotactic chemistry

• Zeolites, TiO2, WO3: channels, cavities

• Graphite, TiS2, NbSe2, MoO3: interlayer spaces

• Beta alumina: interlayer spaces, conduction planes

• Polyacetylene, NbSe3: inter chain channel spaces

TOPOTACTIC SOLID-STATE SYNTHESIS

METHODS: HOST-GUEST INCLUSION CHEMISTRY

• Ion exchange, ion-electron injection, atom, molecule, coordination complex, cluster and polymer, intercalation and occlusion, achievable by non-aqueous and aqueous solution, gas phase and melt phase techniques

• Chemical and electrochemical synthesis methods

• This type of topotactic solid state chemistry creates new materials with novel properties, useful functions and wide ranging applications and myriad technologies

GRAPHITE

A

A

B

out of plane pp orbitals - p/p* delocalized bands

VDW gap 3.35Å

sp2 in plane s bonding

C-C 1.41Å, BO 1.33

ABAB stacked

hexagonal graphite

Pristine graphite - filled p band - empty

p* band - narrow gap - semimetal

GRAPHITE INTERCALATION COMPOUNDS

G (s) + K (melt or vapor) C8K (bronze)

C8K (vacuum, heat) C24K C36K C48K C60K

Staging, distinct phases, ordered guests, K G CT

AAAA sheet stacking sequence

K nesting between parallel eclipsed hexagons,

Typical of many graphite H-G inclusion compounds

4x1/4 K = 1

8x1 C = 8

C8K stoichiometry

GRAPHITE INTERCALATION

ELECTRON DONORS AND ACCEPTORS

SALCAOs of the pp –pp type create the p valence and p*

conduction bands of graphite, very small band gap, essentially

metallic conductivity, single crystal conductivity in-plane 104

times that of out-of plane - thermal, electrical properties tuned

by degree of CB band filling or VB emptying

s

p

p*

s

p

p*

E

N(E)

s

p

p*

C C8Br electron depletion from C2pp VB –

metallic oxidative intercalation

C8K electron transfer to C2pp CB – metallic

reductive intercalation

E(F)

E(F) Eg

CB

VB

INTERCALATION REACTIONS OF GRAPHITE

Always Ask: Oxidative, Reductive or Charge Neutral?

• G (HF/F2/25oC) C3.3F to C40F (white)

• intercalation via HF2- not F- - relative size, charge, ion and dipole,

polarizability effects - less strongly interacting - more facile diffusion

• G (HF/F2/450oC) CF0.68 to CF (white)

• G (H2SO4 conc.) C24(HSO4).2H2SO4 + H2

• G (FeCl3 vapor) CnFeCl3

• G (Br2 vapor) C8Br

PROPERTIES OF INTERCALATED GRAPHITE

• Structural planarity of layers often unaffected by intercalation - bending of layers has been observed - intercalation often reversible

• Modification of thermal and electrical conductivity behavior by tuning degree of p*-CB filling or p-VB emptying

• Anisotropic properties of graphite intercalation systems usually observed

• Layer spacing varies with nature of the guest and loading

• CF: 6.6 Å, C4F: 5.5 Å, C8F: 5.4 Å

BUTTON CELLS

LITHIUM-GRAPHITE FLUORIDE CFx BATTERY

SS contact

Li anode

Li+/PEO

CFx/C/PVDF

cathode

Al contact

e

Li+

F-

LiF

Composite CFx cathode

with C black particles to

enhance electrical

conductivity and

poly(vinylidenedifluoride)

PVDF binder to provide

mechanical stability

BUTTON CELLS

LITHIUM-GRAPHITE FLUORIDE BATTERY

• Cell electrochemistry

• xLi + CFx xLiF + C

• xLi xLi+ + xe-

• Cx+xF- + xLi+ + xe- C + xLiF Nominal cell voltage 2.7 V

• CFx safe storage of fluorine, intercalation of graphite by fluorine

• Millions of batteries sold yearly, first commercial Li battery, Panasonic

• Lightweight high energy density battery - cell requires stainless steel electrode/lithium metal anode/Li+-PEO fast ion conductor/CFx intercalate - acetylene black electrical conductor – poly(vinylidenedifluoride) mechanical support cathode/aluminum charge collector electrode

SYNTHESIS OF BORON AND NITROGEN

GRAPHITES - INTRALAYER DOPING

• New ways of modifying the properties of graphite

• Instead of tuning the degree of CB/VB filling with electrons and holes using the traditional intercalation methods focus on intralayer doping

• Put B or N into the graphite layers, deficient and rich in carriers, enables intralayer doping with holes (VB) and electrons (CB) respectively

• Big question delocalized intraband or localized interband dopant states???

• Also provides access to a new intercalation chemistry

SYNTHESIS OF BC3

THEN PROVING IT IS SINGLE PHASE?

• Traditional heat and beat

• xB + yC (2350oC) BCx

• Maximum 2.35 at% B incorporation in C

• Poor quality not well-defined materials

• New approach, soft chemistry, lower T 800oC , flow reaction, quartz tube – lustrous film formed on glass walls

• 2BCl3 + C6H6 2BC3 + 6HCl

CHEMICAL AND PHYSICAL

CHARACTERIZATION OF BC3

• BC3 + 15/2F2 BF3 + 3CF4

• Fluorine burn technique

• BF3 : CF4 = 1 : 3

• Shows BC3 composition

• No evidence of precursors or intermediates

• Electron and Powder X-Ray Diffraction Analysis

• Shows graphite like interlayer reflections (00l)

CHEMICAL AND PHYSICAL

CHARACTERIZATION OF BC3

• 2BC3 (polycryst) + 3Cl2 (300oC) 6C (amorph) + 2BCl3

• C (cryst graphite) + Cl2 (300oC) C (cryst graphite)

• This neat experiment proves B is truly a "chemical"

constituent of the graphite sheet and not an amorphous

component of a "physical" mixture with graphite

• Synthesis, PXRD structural analysis, chemical and

physical properties all indicate a graphite like structure

for BC3 with an ordered B, C arrangement in the layers

STRUCTURE OF BORON GRAPHITE BC3

Rietfeld PXRD Structure Refinement

4Cx1/4 + 2Cx1/2 + 10Cx1 = 12C

6Bx1/2 + 1Bx1 = 4B

Probable layer atomic arrangement with stoichiometry BC3

CHEMICAL AND PHYSICAL

CHARACTERIZATION OF BC3

• BC3 interlayer spacing similar to graphite

• Also similar to graphite-like BN made from thermolysis of inorganic benzene - borazine B3N3H6 - thinking outside of the box - F doping by using fluorinated borazine!!!

• Four probe basal plane resistivity on BC3 flakes

s(BC3)AB ~ 1.1 s(G)AB, (greater than 2 x 104 ohm-1cm-1)

• Implies B effect is not the un-filling of VB to give a metal but rather the creation of localized states in electronic band gap making boron graphite behave like a substitution site doped

graphite maybe with a larger band gap

• Recall heteronuclear BN is a wide band gap insulator!!!

BOTTOM LINE - ELECTRONIC BAND

DESCRIPTION OF BC3

s

p

p*

s

p

p*

E

N(E)

s

p

p*

C BC3 delocalized states in C2pp VB

E(F) E(F)

Eg

CB

VB

BC3 localized states near C2pp VB

4-PROBE CONDUCTIVITY MEASUREMENTS

I = V1/R1

Rsample = V2/I

Rsample = (V2R1)/V1

r = Rsample (A/L)

s = 1/r

L A

I

V2

V1

R1

Constant

current

source

Ohmeter

REPRESENTATIVE BC3 INTERCALATION CHEMISTRY

• BC3 + S2O6F2 (BC3)2SO3F Oxidative Intercalation

• Note: O2FSO--OSO2F, peroxydisulfuryl fluoride strong oxidizing agent, weak

peroxy-linkage easily reductively cleaved to stable fluorosulfonate anion 2SO3F-

• (BC3)2SO3F Ic = 8.1 Å, (C7)SO3F Ic = 7.73 Å, (BN)3SO3F Ic = 8.06 Å

• BC3 Ic = 3-4 Å , C Ic = 3.35 Å, BN Ic = 3.33 Å

• More Juicy Redox Intercalation Chemistry for BC3

• BC3 + Na+Naphthalide-/THF (BC3)xNa (bronze, first stage, Ic ~ 4.3 Å)

• BC3 + Br2(l) (BC3)15/4Br (deep blue)

INTERCALATION SYNTHESIS OF

TRANSITION METAL DICHALCOGENIDES

• Group IV, V, VI MS2 and MSe2 Compounds

• Layered structures

• Most studied is TiS2

• hcp S2-

• Ti4+ in Oh sites

• Van der Waals gap

INTERCALATION SYNTHESIS OF TRANSITION

METAL DICHALCOGENIDES

• Li+ intercalated between the layers

• Li+ resides in well-defined Td S4 interlayer sites

• Electrons injected into Ti4+ t2g CB states or localized state in electronic bandgap

• LixTiS2 with tunable band filling and unfilling

• Localized xLi(I)xTi(III)(1-x)Ti(IV)S2 mixed valence vs delocalized xLiTi(IV-x)S2 electronic bonding models???

• Hopping semiconductor mixed valence description

xLi(I)xTi(III)(1-x)Ti(IV)S2

• VDW gap prized apart by 10%

ELECTRONIC DESCRIPTION OF LixTiS2

S(-II) 3pp VB

t2g Ti(III) localized

t2g Ti(IV) delocalized

N(E)

E E

• DOS electronic band description LixTix(III)Ti(1-x) (IV)S2 mixed valence localized t2g states (hopping semiconductor - Day and Robin Class II) or LixTi (IV-x)S2 delocalized partially filled t2g band (metal - Day and Robin Class III)

• Distinguished by s(T) temperature dependent electrical conductivity (semiconductor not metal), optical detection of Ti(III) Ti(IV) intervalence charge transfer IVCT blue color and electron paramagnetic resonance EPR detection of unpaired electron on Ti(III)

IVCT

• xC4H9Li + TiS2 (hexane, N2/RT) LixTiS2 + x/2C8H18

• Filter, hexane wash

• 0 x 1

• DOS electronic band description LixTix(III)Ti(1-x)

(IV)S2 mixed valence localized t2g states (hopping semiconductor - Day and Robin Class II) or LixTi

(IV-x)S2 delocalized partially filled t2g band (metal - Day and Robin Class III)

CHEMICAL SYNTHESIS OF LixTiS2

S(-II) 3pp VB

t2g Ti(III) localized

t2g Ti(IV) delocalized

N(E)

E E

SEEING INTERCALATION - DIRECT

VISUALIZATION OPTICAL MICROSCOPY

Intercalating lithium - see the layers spread apart –

device challenge – mechanical stability

ELECTROCHEMICAL SYNTHESIS OF LixTiS2

TiS2 + xLi+ + xe- LixTiS2 AN ATTRACTIVE ENERGY STORAGE SYSTEM???

2.5V open circuit = (EF(Li)-EF(TiS2) - no

current drawn - energy density 4 x

Pb/H2SO4 battery of same weight

Li+

e-

Controlled potential coulometry, voltage

controlled Li+ intercalation where x is

number of equivalents of charge passed

PVDF(filler)/C(conductor)/TiS2/Pt(contact)

composite cathode – mechanical stability

challenge, electronic and ionic conductivity:

TiS2 + xLi+ +xe- LixTiS2

PEO/Li(CF3SO3) polymer-salt solid

electrolyte or propylene carbonate/LiClO4

non aqueous electrolyte

Li metal anode: Li Li+ +e-

LiCoO2

LiCoO2

LixC6

Li

ROCKING CHAIR LSSB

TO AVOID Li DENDRITES

Li/TiS2 AN ATTRACTIVE ENERGY SOURCE BUT

MANY TECHNICAL OBSTACLES TO OVERCOME

• Technical problems to overcome with both the Li anode, intercalation cathode and polymer-salt electrolyte

• Battery cycling causes Li dendritic growth at anode - need other Li-based anode materials, Li-C composites, Li-Sn, Li-Si alloys - also rocking chair LixMO2 configuration

• Mechanical deterioration at the cathode due to multiple intercalation-deintercalation lattice volume expansion-contraction cycles

• Cause lifetime, corrosion, reactivity, and kaboom safety hazards – challenge for large scale electric car LSSB

Fast ionic and electron

conducting materials playground

Nexeion

Unique

Silicon

Anode

Technology

for Next

Generation

Li Ion

Batteries

Why Si Anode ? Gravimetric Capacity and Voltage

Hello Si Goodbye C !

• In contrast to C, the Si anode has a much higher

capacity for lithium ~10x the gravimetric capacity per

gram (mAh/g).

• 6C + Li+ + e- LiC6 = 372 mAh/g

• 4Si + 15Li+ + 15e- Li15Si4 = 3580 mAh/g

• NW Si structures overcome problems of poor cycle life of

bulk Si by mitigating the volume expansion issue –

deliver extended cycle life without degradation of capacity

• Nexion LSSB accommodates the substantial 4x Si anode volume changes on Li insertion by fabricating the anode as an array of Si NWs

• Provide small Li+ diffusion lengths for rapid charge-discharge

• Nanowire conduits for efficient transport of charge to current collectors

• Sufficient space in between nanowires to contain their volume expansion and contraction recycling requirements.

Hello Si Goodbye C !

Synthesis of Si Nanowires

One-step chemical etching involves immersion of clean p-Si substrates in an etchant solution containing 0.01–0.04 M AgNO3 and 5M HF.

Growth Mechanism for Si NW Arrays

Using Electroless Metal Deposition

Self assembly nano-

electrochemistry process

1. Si wafer oxidative etching in

aqueous HF to [SiF6]2-and Ag+

reductive deposition on Si wafer

to ncAg take place simultaneously

2. Deposited Ag forms on the surface

of the substrate forming uniformly

distributed ncAg

3. ncAg and areas surrounding them

act as local cathodes and anodes.

4. Si anodes etched preferentially to

form Ag capped Si nanowires

5. Length of the wire depends on the

etching time.

Hello Si Goodbye C !

• Top - First generation commercially available nano Si is a low cost form capable of capacities of 1000mAh/g.

• Bottom - Second generation nano Si has a different morphology and has been optimized for 3600 mAh/g

• Used with conventional polymer binders PVDF and current collectors as part of the standard battery manufacturing process

OTHER INTERCALATION SYNTHESES WITH TiS2

• Cu+, Ag+, H+, NH3, RNH2, Cp2Co, chemical, electrochemical

• Cobaltacene Cp2Co(II) especially interesting 19e guest

• [Cp2Co(III)]x+Tix

3+Ti1-x4+S2 chemical-electronic description

consistent with structure, hopping SC, optical spectroscopy

• Cp2Co almost spherical, temperature dependent 1H and 13C solid state

NMR shows Cp ring wizzing (lower T) and molecule tumbling dynamics (higher T) with Cp2Co

+ molecular axis orthogonal and parallel to layers, dynamics yields activation energies for the different rotational processes

Co Co

Synthesis, Cp2Co-

CH3CN (solution)-

TiS2(s)

EXPLAINING THE MAXIMUM 3Ti: 1Co

STOICHIOMETRY IN (Cp2Co)0.3TiS2

Interleaved Cp2Co(+) cations

between TiS2 sheets

Matching trigonal symmetry

of hcp chalcogenide sheet

Maximum of third of

interlayer space filled

Geometrical and steric

requirements of close

packing transverse oriented

metallocene in VDV gap

3-D OPEN FRAMEWORK TUNGSTEN OXIDE AND

TUNGSTEN OXIDE BRONZES MxWO3

O

M

W

c-WO3 = c-ReO3 structure type with

injected cation xM(q+) center of

cube and charge balancing xqe-

MxWO3 Perovskite structure type

M(q+) O CN = 12, O(2-) W CN = 2,

W(VI) O CN = 6

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 ( )

xM(q+) intercalated between

sheets with charge balancing xqe MxMoO3

ELECTROCHEMICAL OR CHEMICAL

SYNTHESIS OF MxWO3

• xNa+ + xe- + WO3 NaxWx5+W1-x

6+O3

• xH+ + xe- + WO3 HxWx5+W1-x

6+O3

• Injection of alkali metal cations generates Perovskite

structure types

• M+ oxygen coordination number 12, resides at center of cube

• H+ protonates oxygen framework, exists as MOH groups

SYNTHESIS DETAILS FOR Mx’MO3 WHERE M = Mo, W AND M’ = INJECTED PROTON

OR ALKALI OR ALKALINE EARTH CATION

• n BuLi/hexane CHEMICAL

• LiI/CH3CN

• Zn/HCl/aqueous

• Na2S2O4 aqueous alkaline sodium dithionite

• S2O4(2-) + 4OH(-) 2SO3(2-) + 2H2O + 2e

• Pt/H2

• Topotactic ion-exchange of Mx’MO3 with M” cation

• Li/LiClO4/MO3 ELECTROCHEMICAL

• Cathodic reduction in aqueous acid electrolyte

• MO3 + H2SO4 (0.1M) HxMO3

VPT GROWTH OF LARGE SINGLE CRYSTALS OF

MOLYBDENUM AND TUNGSTEN TRIOXIDE AND

CVD GROWTH OF LARGE AREA THIN FILMS

• VPT CRYSTAL GROWTH

• MO3 + 2Cl2 (700°C) (800°C) MO2Cl2 + Cl2O

• CVD THIN FILM GROWTH

• M(CO)6 + 9/2O2 (500°C) MO3 + 6CO2

MANY APPLICATIONS OF THIS M’xMO3

CHEMISTRY AND MATERIALS

• Electrochemical devices like pH sensors, electrochromic displays, electrochromic energy saving windows, lithium solid state battery cathodes, proton conducting solid electrolytes in H2-O2 fuel cell

• Behave as low dopant mixed valance hopping semiconductors

• Behave as high dopant metals

• Electrical and optical properties best understood by reference to simple DOS picture of

M’xMx5+M1-x

6+O3

COLORING MOLYBDENUM TRIOXIDE WITH

PROTONS, MAKING IT ELECTRONICALLY, IONICALLY

CONDUCTIVE AND A SOLID BRNSTED ACID

Electronic band structure in HxMoO3 molybdenum oxide bronze, tuning color,

electronic conductivity, acidity with x

COLOR OF TUNGSTEN BRONZES, MxWO3

INTERVALENCE W(V) TO W(VI) CHARGE TRANSFER

IVCT

ELECTRONIC AND COLOR CHANGES BEST

UNDERSTOOD BY REFERENCE TO SIMPLE BAND

PICTURE OF NaxMox5+Mo1-x

6+O3

• SEMICONDUCTOR TO METAL TRANSITION ON DOPING MxMoO3

• MoO3: Band gap excitation from O2-

(2pp) VB to Mo6+ (5d) CB, LMCT in UV region, wide band gap insulator

• NaxMox5+Mo1-x

6+O3: Low doping level, narrow band gap hopping semiconductor, narrow localized Mo5+ (d1) VB, visible absorption, essentially IVCT Mo5+ to Mo6+ absorption, mixed valence hopping semiconductor

• NaxMox5+Mo1-x

6+O3: High doping level, partially filled valence band, narrow delocalized Mo5+ (d1) VB, visible absorption, IVCT Mo5+ to Mo6+ and shows metallic reflectivity (optical plasmon) and metallic conductivity

HxMoO3 TOPOTACTIC PROTON INSERTION

• Range of compositions: 0 < x < 2

• MoO3 structure largely unaltered by reaction - four phases

• 0.23 < x < 0.4 orthorhombic

• 0.85 < x < 1.04 monoclinic

• 1.55 < x < 1.72 monoclinic

• 2.00 = x monoclinic

• Similar lattice parameters by XRD, ND of HxMoO3 compared to parent MoO3

• MoO3 high resistivity semiconductor

• HxMoO3 insertion material SC to M transition

• HxMoO3 strong Brnsted acid: Mo-O(H)-Mo solid acid catalysts

• HxMoO3 fast proton conductor: Mo-O(H)-Mo-O proton oxygen site to site hopping – useful in solid electrolyte in H2-O2 fuel cells

• What happens when single crystal immersed in Zn/HCl/H2O H(+) + e(-)?

BASICS OF H2+O2 H2O FUEL CELL WITH PROTON CONDUCTING MEMBRANE

Proton conducting

membrane allows only the

protons to pass

Proton conducting

membrane

INTRALAYER PROTON DIFFUSION

1-D proton conduction along chains

Yellow transparent

Protons begin in basal plane

Moves from two edges along c-axis

INTERLAYER PROTON DIFFUSION

b-axis adjoining layers react Orange transparent (semiconducting)

PROTON FILLING

Eventually proton diffusion complete and

entire crystal transformed Blue bronze

Consistent with structural, electrical and

optical data (metallic)

HxMoO3 TOPOTACTIC PROTON INSERTION

PROTON CONDUCTION PATHWAY IN HxMoO3

c-axis

PROTON CONDUCTION

PATHWAY IN HxMoO3

• Part of a HxMoO3 layer

• Showing initial 1-D proton conduction pathway

• Apical to triply bridging oxygen proton migration first

• 1H wide line NMR, PGSE NMR probes of structure and diffusion

• Doubly to triply bridging oxygen proton migration pathway

• Initial proton mobility along c-axis intralayer direction for x = 0.3

• Subsequently along b-axis interlayer direction

• Single protonation at x = 0.36, double protonation x = 1.7

• More mobile protons higher loading D(300K) ~ 10-11 vs 10-9 cm2s-1

• Proton-proton repulsion

ION EXCHANGE SOLID STATE SYNTHESIS

• Requirements: anionic open channel, layer or framework structure

• Replacement of some or all of charge balancing cations by protons or simple or complex cations

• Classic cation exchangers are zeolites, clays, beta-alumina, molybdenum and tungsten oxide bronzes, lithium intercalated metal dichalcogenides

BETA ALUMINA

• High T synthesis of beta-alumina:

• (1+x)/2Na2O + 5.5Al2O3 Na1+xAl11O17+x/2

• Structural reminders (x ~ 0.2):

• Na2O: Antifluorite ccp Na+, O2- in Td sites

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

• Na1+xAl11O17+x/2 defect Spinel, O2- vacancies in conduction

plane, controlled by x ~ 0.2, Spinel blocks 9Å thick, bridging oxygen columns, mobile Na+ cations in conduction plane

• 2-D fast sodium ion conductor

Rigid Al-O-Al

column spacers

3/4 O(2-) missing in

conduction plane

0.9 nm

Na1+xAl11O17+x/2 defect spinel

blocks

Na(+) conduction

plane

Spinel blocks, ccp layers of O(2-)

Every 5th. layer has 3/4 O(2-) vacant, defect spinel

4 ccp layers have 1/2Oh, 1/8Td Al( 3+) cation sites

Blocks cemented by rigid Al-O-Al spacers

Na(+) mobile in 5th open conduction plane

Centrosymmetric layer sequence in Na1+xAl11O17+x/2 (ABCA)B(ACBA)C(ABCA)B(ACBA)

GETTING BETWEEN THE SHEETS OF THE BETA

ALUMINA FAST SODIUM CATION FAST ION

CONDUCTOR: LIVING IN THE FAST LANE

Al-O-Al column

spacers in conduction

plane

Mobile sodium cations

Oxide wall of

conduction plane

0.9 nm Spinel block

ION EXCHANGE IN Na1+xAl11O17+x/2

Thermodynamic and

kinetic considerations

Mass, size and charge

considerations

Lattice energy controls

stability of ion-

exchanged materials

Cation diffusion,

polarizability effects

control rate of ion-

exchange

MELT ION-EXCHANGE OF CRYSTALS

• Equilibria between beta-alumina and MNO3 and MCl melts, 300-350oC

• Extent of exchange depends on time, T, melt composition

• Monovalents: Li+, K+, Rb+, Ag+, Cu+, Tl+, NH4+, In+, Ga+,

NO+, H3O+

• Higher valent cations: Ca2+, Eu3+, Pb2+

• Higher T melts required for exchange of higher valency cations, strong cation binding, slower cation diffusion, 600-800oC typical

MELT ION-EXCHANGE OF CRYSTALS

• Charge-balance requirements:

• 2Na+ for 1Ca2+, 3Na+ for 1La3+

• Controlled partial exchange by

control of melt composition:

• qNaNO3 : (1-q)AgNO3

• Na1+x-yAgyAl11O17+x/2

WHAT CONTROLS KINETICS AND

THERMODYNAMICS OF SOLID STATE ION

EXCHANGE

• Kinetics of Ion-Exchange

• Controlled by ionic mobility of the cation

• Mass, charge, radius, temperature, solvent, solid state structural properties

• Thermodynamics, Extent of Ion-Exchange

• Ion-exchange equilibrium for cations

• Binding activities between melt and crystal phases

• Crystal lattice site preferences

• Binding energetics, lattice energies

• Charge : radius ratios