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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

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topotactic solid state synthesis methods host guest inclusion chemistry
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
TOPOTAXY: HOST-GUEST INCLUSION

1D- Tunnel Structures

2D- Layered Structures

-TiO2

-hWO3

-TiS3

3D-Frameworks

-Graphite

-TiS2

-TiO2(B)

-KxMnO2

-FeOCl

-HxMoO3

-b alumina

-LixCoO2

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

-zeolites

-LiMn2O4

-cWO3

topotactic solid state synthesis methods host guest inclusion chemistry3
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 chemistry4
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

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

sp2 in plane s bonding

A

VDW gap 3.35Å

B

C-C 1.41Å, BO 1.33

A

ABAB stacked hexagonal graphite

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

GRAPHITE
graphite intercalation compounds
GRAPHITE INTERCALATION COMPOUNDS

4x1/4 K = 1

8x1 C = 8

C8K stoichiometry

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

graphite intercalation electron donors and acceptors

E

C

C8K electron transfer to C2pp CB – metallic reductive intercalation

C8Br electron depletion from C2pp VB – metallic oxidative intercalation

p*

p*

CB

p*

E(F)

Eg

E(F)

p

p

VB

p

N(E)

GRAPHITE INTERCALATION ELECTRON DONORS AND ACCEPTORS

SALCAOs of the p-pi-type create the p valence and p* 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

intercalation reactions of graphite oxidative reductive or charge neutral
INTERCALATION REACTIONS OF GRAPHITEOxidative, 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
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 battery

Composite CFx cathode with C black particles to enhance electrical conductivity and poly(vinylidenedifluoride) PVDF binder to provide mechanical stability

e

F-

LiF

Al contact

SS contact

Li+

Li anode

CFx/C/PVDF cathode

Li+/PEO

BUTTON CELLS LITHIUM-GRAPHITE FLUORIDE BATTERY
button cells lithium graphite fluoride battery11
BUTTON CELLSLITHIUM-GRAPHITE FLUORIDE BATTERY
  • Cell electrochemistry
  • xLi + CFx xLiF + C
  • xLi  xLi+ + e-
  • Cx+xF- + xLi+ + xe- C + xLiFNominal 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
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
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 bc 3 then proving it is single phase
SYNTHESIS OF AND BC3THEN 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 bc 3
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 bc 317
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 bc 3 rietfeld pxrd structure refinement
STRUCTURE OF BORON GRAPHITE BC3Rietfeld 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 bc 319
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 unfilling of VB to give a metal but rather the creation of localized states in electronic band gap making boron graphite behave like a substitutionlly doped graphite maybe with a larger band gap – recall BN is a wide band gap insulator!!!
4 probe conductivity measurements

L

A

I = V1/R1

Rsample = V2/I

Rsample = (V2R1)/V1

r= Rsample (A/L)

s = 1/r

I

V1

V2

Constant current source

R1

Ohmeter

4-PROBE CONDUCTIVITY MEASUREMENTS
representative bc 3 intercalation chemistry
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 c 5 n
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 sheets intercalation facilitated exfoliation
Soft Synthesis of Single-Crystal Silicon Monolayer SheetsIntercalation Facilitated Exfoliation

Structural model of CaSi2

synthesis of silicon nanosheets
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 nanosheets25
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
optical properties of silicon nanosheets
OPTICAL PROPERTIES OF SILICON NANOSHEETS
  • RT optical properties of Si nanosheets
  • UV/Vis spectra of suspensions of Si Nanosheets at various concentrations. Inset: the absorbance at 268 nm is plotted against concentration of sheets.
  • 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
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 dichalcogenides29
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) electronic bonding models???
  • VDW gap prized apart by 10%
seeing intercalation direct visualization optical microscopy
SEEING INTERCALATION - DIRECT VISUALIZATION OPTICAL MICROSCOPY

Intercalating lithium - see the layers spread apart

electrochemical synthesis of li x tis 2 tis 2 xli xe li x tis 2 an attractive energy storage system

e-

Li+

ELECTROCHEMICAL SYNTHESIS OF LixTiS2TiS2 + xLi+ + xe- LixTiS2AN 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

Controlled potential coulometry, voltage controlled Li+ intercalation where x is number of equivalents of charge passed

Li metal anode: Li  Li+ +e-

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

PVDF(filler)/C(conductor)/TiS2/Pt(contact) composite cathode:

TiS2 + xLi+ +xe- LixTiS2

chemical synthesis of li x tis 2

E

E

t2g Ti(IV) delocalized

t2g Ti(III) localized

S(-II) 3pp VB

N(E)

CHEMICAL SYNTHESIS OF LixTiS2
  • 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)
li tis 2 an attractive energy source but many technical obstacles to overcome
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 kaboom safety hazards
slide34

LiCoO2

LixC6

ROCKING CHAIR LSSB

Li

LiCoO2

other intercalation syntheses with tis 2

Co

Co

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-x4+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

Synthesis, Cp2Co-CH3CN (solution)-TiS2(s)

explaining the maximum 3ti 1co stoichiometry in cp 2 co 0 3 tis 2
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

slide37
Inhibition of Energy Transfer between Conjugated Polymer Chains in Host-Guest Nanocomposites Generates White Photo- and Electroluminescence
pxrd diagnostics
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
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
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)
slide41

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

LixTiS3

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

FACE BRIDGING OCTAHEDRAL TITANIUM TRISULFIDE AND NIOBIUM TRISELENIDE BUILDING BLOCKS FORM 1-D CHAINS
3 d open framework tungsten oxide and tungsten oxide bronzes m x wo 3

W

O

M

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

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

slide43

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 m x wo 3
ELECTROCHEMICAL OR CHEMICAL SYNTHESIS OF MxWO3
  • xNa+ + xe- + WO3 NaxWx5+W1-x6+O3
  • xH+ + xe- + WO3 HxWx5+W1-x6+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
slide45
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 sodium dithionate
  • Pt/H2
  • Topotactic ion-exchange of Mx’MO3 with M” cation
  • Li/LiClO4/MO3ELECTROCHEMICAL
  • Cathodic reduction in aqueous acid electrolyte
  • MO3 + H2SO4 (0.1M) Û HxMO3
slide46
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) Û(800°C) MO2Cl2 + Cl2O
  • CVD THIN FILM GROWTH
  • M(CO)6 + 9/2O2 (500°C)  MO3 + 6CO2
many applications of this m x mo 3 chemistry and materials
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 properties best understood by reference to simple DOS picture of M’xMx5+M1-x6+O3
slide48

COLORING MOLYBDENUM TRIOXIDE WITHPROTONS, MAKING IT ELECTRONICALLY, IONICALLY CONDUCTIVE AND A SOLID BRNSTED ACIDElectronic band structure in HxMoO3 molybdenum oxide bronze, tuning color, electronic conductivity, acidity with x

slide50
ELECTRONIC AND COLOR CHANGES BEST UNDERSTOOD BY REFERENCE TO SIMPLE BAND PICTURE OF NaxMox5+Mo1-x6+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-x6+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-x6+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
h x moo 3 topotactic proton insertion
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
  • MoO3 high resistivity semiconductor
  • HxMoO3 insertion material SC to M transition
  • HxMoO3 strong Brnsted acid – Mo-O(H)-Mo
  • HxMoO3 fast proton conductor
  • See what happens when single crystal immersed in Zn/HCl/H2O
slide52

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

PROTON FILLING

Eventually proton diffusion complete and entire crystal transformed Blue bronze

Consistent with structural, electrical and optical data

HxMoO3 TOPOTACTIC PROTON INSERTION

proton conduction pathway in h x moo 354
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) ~ 10-11vs 10-9 cm2s-1
  • Proton-proton repulsion
ion exchange solid state synthesis
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
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
  • Na1+xAl11O17+x/2 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
slide57

Rigid Al-O-Al column spacers

Na(+) conduction plane

0.9 nm Na1+xAl11O17+x/2 defect spinel blocks

3/4 O(2-) missing in 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)

slide58

0.9 nm Spinel block

Al-O-Al column spacers in conduction plane

Oxide wall of conduction plane

Mobile sodium cations

GETTING BETWEEN THE SHEETS OF THE BETA ALUMINA FAST SODIUM CATION FAST ION CONDUCTOR: LIVING IN THE FAST LANE
ion exchange in na 1 x al 11 o 17 x 2
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
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 crystals63
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 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