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/crystals

TOPOTAXY: HOST-GUEST INCLUSION

1D- Tunnel Structures

-TiO2

-hWO3

-TiS3

2D- Layered Structures

-Graphite-TiS2

-TiO2(B)-KxMnO2

-FeOCl-HxMoO3

-alumina-LixCoO2

3D-Frameworks

-zeolites-LiMn2O4

-cWO3

Pivotal topotactic materials properties for functional utility in Li solid state battery electodes, electrochromic mirrors and windows, fuel and solar cell electrolytes and electrodes, chemical sensors, superconductors

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 intercalation and occlusion, achievable by non-aqueous, aqueous, gas phase, melt techniques

• Chemical, 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 p orbitals - * delocalized bands

VDW gap 3.35Å

sp2 in plane bonding

C-C 1.41Å, BO 1.33

ABAB stacked hexagonal graphite

Pristine graphite - filled band - empty * band - narrow gap - semimetal

GRAPHITE INTERCALATION COMPOUNDS

G (s) + K (melt or vapor) C8K (bronze) C8K (vacuum, heat) C24K C36K C48K C60KStaging, distinct phases, ordered guests, K G CTAAAA 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 -pi-type create the valence and * conduction bands of graphite, very small band gap, essentially

metallic conductivity, single crystal properties in-plane 104 times that of out-of plane conductivity - thermal, electrical

properties tuned by degree of CB band filling or VB emptying

E

N(E)

C C8Br electron depletion

from C2p VB – metallic oxidative intercalation

C8K electron transfer to

C2p CB – metallic reductive intercalation

E(F)

E(F)Eg

CB

VB

INTERCALATION REACTIONS OF GRAPHITE

Oxidative, Reductive or Charge Neutral?Oxidative, Reductive or Charge Neutral?

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

• intercalation via HF2- not F- - relative size, charge, ion, 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 *-CB filling or 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 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 CELLSLITHIUM-GRAPHITE FLUORIDE BATTERY

• Cell electrochemistryCell electrochemistry

• xLi + CFx xLiF + C• xLi xLi+ + e-

• 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

C60-G INTERCALATING BUCKBALL INTO GRAPHITE

NEW HYDROGEN STORAGE MATERIAL

• Thermally induced 600oC intercalation of C60 into G

• Hexagonal close packed C60 between graphene sheets

• Sieves H2 from larger N2

• Physisorbed H2 in intralayer void spaces

• Rapid adsorption-desorption

• Dead capacity because of volume occupied by C60

• Capacity possibly enhanced by reducing filling fraction of C60

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 methods focus on interlayer doping

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

• Also provides a new intercalation chemistry

SYNTHESIS OF AND 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, low T, flow reaction, quartz tube

• 2BCl3 + C6H6 (800oC) 2BC3 (lustrous film on walls) + 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, analysis, structural findings 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 RefinementRietfeld 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

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

• Implies B effect is not the unfilling of VB to give a metal but Implies B effect is not the unfilling of VB to give a metal but rather the creation of localized states in electronic band gap rather the creation of localized states in electronic band gap making boron graphite behave like a substitutionlly doped making boron graphite behave like a substitutionlly doped graphite maybe with a larger band gap – recall BN is a wide graphite maybe with a larger band gap – recall BN is a wide band gap insulator!!!band gap insulator!!!

4-PROBE CONDUCTIVITY MEASUREMENTS4-PROBE CONDUCTIVITY MEASUREMENTS

I = V1/R1

Rsample = V2/I

Rsample = (V2R1)/V1

= Rsample (A/L)

= 1

LA

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)

ATTEMPT TO INCORPORATE NITROGEN INTO THE GRAPHITE SHEETS, EVIDENCE FOR C5N

• Pyridine + Cl2 (800oC, flow, quartz tube) silvery deposit (PXRD Ic ~ 3.42 Å)

• Fluorine burning of silver deposit CF4/NF3/N2

• No signs of HF, ClF1,3,5 in F2 burning reaction

• Superior conductivity wrt graphite?

• Try to balance the fluorine burning reaction to give the nitrogen graphite stoichiometry of C5N - a challenge for your senses!!! 4C5N + 43F2 20CF4 + 2NF3 + N2

Soft Synthesis of Single-Crystal Silicon Monolayer SheetsIntercalation Facilitated Exfoliation

Structural model of CaSi2

SYNTHESIS OF SILICON NANOSHEETS

• Chemical exfoliation of calcium disilicide, CaSi2• CaSi2 synthesized from stoichiometric amounts

CaSi, Si, Mg, Cu crucible, RF heating, Ar atmosphere, cool to RT, product plate-like crystals

• Hexagonal layered structure (a) consisting of alternating Ca layers and corrugated Si (111) planes in which the Si6 rings are interconnected

• To exfoliate precursor-layered crystals into their elementary layers must adjust the charge on the Si layer.

• Because CaSi2 is ionic (i.e. Ca2+(Si)2) the electrostatic interaction between the Ca2+ and Si layers is strong so key is to reduce charge on the negatively charged silicon layers.

SYNTHESIS OF SILICON NANOSHEETS

• Mg-doped CaSi2 prepared CaSi1.85Mg0.15 in which Mg was doped by ion exchange into the CaSi2 or direct synthesis

• Si monolayer sheets (b, c) prepared through chemical exfoliation of CaSi1.85Mg0.15 by immersion in a solution of propylamine hydrochloride (PA·HCl),

• Ca(2+) ions are de-intercalated and converted into a dispersion of silicon sheets charge balanced by PAH(+)

• The composition of monolayer silicon sheets was determined by XPS to be Si:Mg:O=7.0:1.3:7.5, structure by XRD, ED, TEM, AFM

CHARACTERIZATION OF SILICON NANOSHEETS TEM, ED, XRD, AFM

OPTICAL PROPERTIES OF SILICON NANOSHEETS

RT optical properties of Si nanosheets

a) UV/Vis spectra of suspensions of Si Nanosheets at various concentrations. Inset: the absorbance at 268 nm is plotted against concentration of sheets.

b) PL spectra of Si Nanosheets dispersed in water with an excitation wavelength of 350 nm (indicated by an arrow).

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

• LixTiS2 with tunable band filling and unfilling

• Localized xTi(III)-(1-x) Ti(IV) vs delocalized Ti(IV-x) Localized xTi(III)-(1-x) Ti(IV) vs delocalized Ti(IV-x) electronic bonding models???electronic bonding models???

• VDW gap prized apart by 10%

SEEING INTERCALATION - DIRECT VISUALIZATION OPTICAL MICROSCOPY

Intercalating lithium - see the layers spread apart

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: TiS2 + xLi+ +xe- LixTiS2

PEO/Li(CF3SO3) polymer-salt electrolyte or propylene carbonate/LiClO4 non aqueous electrolyte

Li metal anode: Li Li+ +e-

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

• Filter, hexane wash

• 0 x 1

• Electronic 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) 3p VB

t2g Ti(III) localized

t2g Ti(IV) delocalized

N(E)

E E

Li/TiS2 AN ATTRACTIVE ENERGY SOURCE BUT MANY TECHNICAL OBSTACLES TO OVERCOME

• Technical problems need to be 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 expansion-contraction cycles

• Cause lifetime, corrosion, reactivity, and Cause lifetime, corrosion, reactivity, and kaboomkaboom safety safety hazardshazards

LiCoO2

LiCoO2

LixC6

Li

ROCKING CHAIR LSSB

OTHER INTERCALATION SYNTHESES WITH TiS2

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

• Cobaltacene Cp2Co(II) especially interesting 19e guest • [Cp2Co(III)]x

+Tix3+Ti1-x

4+S2 chemical-electronic description consistent with structure, hopping SC, spectroscopy

• Temperature dependent solid state NMR shows two forms of 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

Matching trigonal symmetry of hcp chalcogenide sheet

Third of interlayer space filled

Geometrical and steric requirements of packing transverse oriented metallocene in VDV gap

Inhibition of Energy Transfer between Conjugated Polymer Chains in Host-Guest Nanocomposites Generates White

Photo- and Electroluminescence

PXRD DIAGNOSTICS

• Chemical structures of blue-emitting PFO, green-emitting F8BT, and red-emitting MEH-PPV

• XRD patterns of a restacked SnS2 film (no polymer), and a blend-intercalated-SnS2 nanocomposite film.

WHITE LIGHT LED DIAGNOSTICS

• PL spectra of separate SnS2/conjugated-polymer-intercalated nanocomposites,

• Blend of only the three polymers (excitation 380 nm),

• PL (excitation 380 nm) and EL of a blend-intercalated/SnS2 nanocomposite film.

• Inset: excitation spectra for emission at 580 nm of a blend of only the three polymers and the blend-intercalated/SnS2 nanocomposite.

INTERCALATION ZOO

• Channel, layer and framework materials

• 1-D chains: TiO2 channels, (TiS3 [Ti(IV)S(2-)S2(2-)], NbSe3 [Nb(IV)Se(2-)Se2(2-)]), contain disulfide and diselenide units in Oh building blocks to form chain

• 2-D layers: MS2, MSe2, NiPS3 [Ni2(P2S6), ABA CdI2 type packing, alternating layers of octahedral NiS6 and trigonal P2S6 groupings with S…S Van der Waals gap], FeOCl, V2O5.nH2O, MoO3, TiO2

(layered polymorph B – see Chimie Douce later)

• 3D framework: zeolites, WO3, Mo6S8, Mo6Se8 (Chevrel phases)

FACE BRIDGING OCTAHEDRAL TITANIUM TRISULFIDE AND NIOBIUM TRISELENIDE

BUILDING BLOCKS FORM 1-D CHAINS

Ti(IV) = S2(2-) = S(2-) = Li(+) =

TiS3 = Ti(IV)S(2-)S2(2-) intercalated cations like Li(+) in channels between chains to formLixTiS3

3-D OPEN FRAMEWORK TUNGSTEN OXIDE AND TUNGSTEN OXIDE BRONZES MxWO3

OO

M

WW

c-WO3 = c-ReO3 structure type with injected cation M(q+) center of cube and charge balancing qe- in CB, 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 ( )

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 CHEMICALCHEMICAL• LiI/CH3CN• Zn/HCl/aqueous• Na2S2O4 aqueous sodium dithionate• Pt/H2

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

• Li/LiClO4/MO3 ELECTROCHEMICALELECTROCHEMICAL• 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 GROWTHVPT CRYSTAL GROWTH

• MO3 + 2Cl2 (700°C) (800°C) MOMO22ClCl22 + Cl2O

• CVD THIN FILM GROWTHCVD THIN FILM GROWTH

• M(CO)6 + 9/2O2 (500°C) MO3 + 6CO2

MANY APPLICATIONS OF THIS M’xMO3 CHEMISTRY AND MATERIALS

• Electrochemical devices like chemical sensors, pH responsive microelectrochemical chips and electrochromic displays, smart windows, advanced batteries

• Behave as low dopant mixed valance hopping semiconductors

• Behave as high dopant metals

• Electrical and optical propertiesElectrical and optical properties best understood by reference to simple DOS picture of M’xMx

5+M1-x6+O3

COLORING MOLYBDENUM TRIOXIDE WITHPROTONS, 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-

(2p) 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 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 cf MoO3

• MoOMoO33 high resistivity semiconductor high resistivity semiconductor• HHxxMoOMoO33 insertion material SC to M transition insertion material SC to M transition• HHxxMoOMoO33 strong Br strong Brnsted acid – Mo-O(nsted acid – Mo-O(HH)-Mo)-Mo• HHxxMoOMoO33 fast proton conductor fast proton conductor

• See what happens when single crystal immersed in Zn/HCl/H2O

INTRALAYER PROTON DIFFUSION1-D proton conduction along chainsYellow transparentProtons begin in basal plane

Moves from two edges along c-axis

INTERLAYER PROTON DIFFUSION

b-axis adjoining layers reactOrange transparent

PROTON FILLINGEventually proton diffusion complete and entire crystal transformed Blue bronzeConsistent with structural, electrical and optical data

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

BETA ALUMINA

• High T synthesis of beta-alumina:

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

• Structural reminders:

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

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

• NaNa1+x1+xAlAl1111OO17+x/217+x/2 defect Spinel defect Spinel, O2- vacancies in conduction plane, controlled by x ~ 0.2, Spinel blocks 9Å, bridging oxygen columns, mobile Na+ cations in conduction plane, 2-D fast-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 spinel4 ccp layers have 1/2Oh, 1/8Td Al( 3+) cation sitesBlocks cemented by rigid Al-O-Al spacersNa(+) 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 exhigher valent 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

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• Site preferences• Binding energetics, lattice energies• Charge : radius ratios