1
5 Some Important Crystal
Structures
Why we need to know some
important crystal
structures?
Three Ways to Describe Crystal Structures
Three Structural sketches of P4O10 molecules:
(a)Stick-ball model： showing that the P-O chemical bond is the
tetrahedral coordination and sp3 covalent bonds.
(b)ion-stacking model： showing O2- forms close packing and P5+
exists in tetrahedral interstitials.
(c)coordination polyhedron model: showing that the connection
of the tetrahedral coordination and tetrahedron, and the
octahedral interstitials is unoccupied.
I
Gemstone
Sapphire
GarnetTopaz
Synthetic ZrO2
Diamond
Three simple ways:
1.X-ray diffraction.
2.Density test.
3.Fog test:
Put the rock in front of your mouth and fog it like
you would try to fog a mirror. If it stays fogged for
2-4 seconds, it’s a fake. A real diamond disperses
the heat instantaneously ， so by the time you look
at it, it has already cleared up.
How Can I Tell If My Diamond Is the
Real Thing, Not Cubic ZrO2?
Physical Properties of Crystals
Crystal form & habit
Cleavage & fracture
Hardness
Specific gravity
Luster
Color
Streak
Taste
Reaction to Acid
Other…
Form & Habit
Form: directly reflects the underlying atomic
structure (bonding, symmetry, etc.). Constant
interfacial angles.
Habit: the characteristic way the mineral
grows. Does not always conform to the form e.g.
nice perfect crystals, and depends of where
grows and how made.
2
2D Similarity of NaCl(111) and Urea(111)
(3 Cl? constitute equilateral
triangle; 3 urea molecules constitute
triangle. Compare the two
triangles,the lateral length of the
latter is twice that of the former.
(octahedral NaCl crystal can be
crystallized from the supersaturated
solution of NaCl with urea.
Absorption of Urea (111) on the
NaCl (111) planes cause the growth
rate of NaCl (111) rather slower
than that of NaCl (100).
(The 2D similarity of crystal
structure cause such phenomena.
Epitaxy Growth of Crystal
When epitaxy growth, both gas and
liquid, the match of lattice parameter
should be considered.
For example, in preparation of
YBa2Cu3O7-δ superconducting thin
film, (a=3.88 ?, b=3.82 ?)， the
substrate can be the single crystal
slice: SrTiO3(100), a=3.91 ? 。
In hydrothermal deposition of TiO2 thin film on
Si(100), the lattice parameter of TiO2: (a=5.354 ?,
b=10.917 ?), d112=2asi,(a=5.43 ?, 2a=10.86 ?), so grow
TiO2 thin film with high 112 orientation.
Carbon shows both Layer and Cage Networks
Carbon Allotropes
Diamond
Graphite
Diamond sp
3 hybrid C
Td group
One of the
strongest/hardest material
known
High thermal conductivity
(unlike ceramics)
Transparent in the visible
and infrared, with high index
of refraction.
Semiconductor (can be
doped to make electronic
devices)
Metastable (transforms to
carbon when heated)
Sphalerite (ZnS) vs Diamond Structure
Ball and stick
shows us the 4-fold
coordination in both
structures
Looking at
tetrahedra in the
structure helps us
see the “diamond
shape”
3
Structures with the Diamond Framework
Diamond
The diamond network
with a single atom type
Zinc Blende (ZnS)
The diamond network
with alternate Zn & S
atoms
The phase diagram for
diamond and graphite
(from J. Geophys. Res.
1980, 85, B12, 6930.)
Reaction Energy vs Structure
(gray tin, diamond
structure, stable
below 13oC)
tetrahedral
white tin
Pressure vs Structure
pressure
+ P
? P
The transformation of
sodium chloride from
the rock salt to the
cesium chloride
structure can be
accomplished at 298 K
at high P (~105 atm).
pressure
Structures of Ionic Solids
Ionic structures are prototypes for a wide range
of solids:
Many of structures effectively described as close
packed anions (occasionally cations) with
interstitial holes filled by cations (occasionally
anions).
Some Rules for Counting Atoms in a Unit Cell
1.Body: An ion in the body of a cell belongs
entirely to that cell and counts as one atom
2.Face: An ion on a face is shared by two cells and
contributes ? atom to the cell in question
3.Edge: An ion on an edge is shared by four cells
and contributes ? atom to the count
4.Corner: An ion on a corner is shared by eight
cells and contributes 1/8 atom to the count
Structures of Ionic Solids based on CCP
4
Polyhedral Representations
Defining the coordination environment of an ion as a
polyhedron
Structures of Ionic Solids
Polyhedral
representations
of structures by
linking
coordination
polyhedra together
Some variations achieved by different filling of
interstitial holes
Structures of Ionic Solids
Formula Type and fraction of sites
occupied
CCP HCP
All octahedral NaCl
Rock Salt
NiAs
Nickel Arsenide
AB
Half tetrahedral
(T+ or T-)
ZnS
Sphalerite
ZnS
Wurtzite
AB2 All tetrahedral Na 2O Anti- Fluorite
CaF2 Fluorite
n ot known
AB3 All octahedral
& tetrahedral
Li3Bi not known
Half octahedral (Alternate
layers full/empty)
CdCl2
CdI2
A2B
Half octahedral (Ordered
framework arrangement)
TiO 2 (Anatase) CaCl2
TiO2 (Rutile)
A3B Third octahedral
Alternate layers 2/3 full/empty
YCl3 BiI3
Locations of Octahedral Holes
in FCC Structure
The Rock Salt Structure
Rock Salt Structure
Interstitial Hole Filling
Structures of Ionic Solids based on CCP
FCC
Sodium Chloride Structure
NaF, NaBr, NaI, LiX, KX, RbX, AgF, AgCl, AgBr, MgO,
CaO, SrO, BaO, MnO, CoO, NiO, CdO, NaH, MgS, CaS,
SrS, BaS (X=halides)
Na+ = 6 x ?+ 8 x 1/8
= 4 ions in cell
Cl? = 1 + 12 x ?
= 4 ions in cell1 ?
?
?
?
?
?
1/8
1/8
1/8
1/8
1/8
1/8
1/8
1/8
?
?
?
?
?
?
?
?
?
??
?
Structures of Ionic Solids based on CCP
Counting Atoms
5
Nearest (N) and Next-Nearest (NN) Neighbors
C
N
N
NN
N
N
NN
NN
NN
NN
NN
NN
NN
NN
NN
NN
NN
NN
Structures of Ionic Solids based on CCP Rock Salt (NaCl) Structure
NaCl; CCP, O sites: 100%
?Motif: Cl at (0,0,0); Cs at (1/2,1/2,1/2)
?1CsCl in unit cell
?Coordination: 8:8 (cubic)
?Adoption by chlorides, bromides and
iodides of larger cations,
?e.g. Cs+, Tl+, NH4+
CsCl
The Rock Salt Structure
Coordination Numbers
CN of each type of
ion is 6
(6,6)
coordination
Cation CN Anion CN
Structures of Ionic Solids based on CCP
Rock Salt Structure ? Summary
CCP Cl- with Na+ in all Octahedral holes
Lattice: FCC
Motif: Clat (0,0,0); Na at (1/2,0,0)
4NaCl in unit cell
Coordination: 6:6 (octahedral)
Cation and anion sites are topologically
identical
Structures of Ionic Solids based on CCP
CCP Ca 2+ with F? in all Tetrahedral holes
Lattice: FCC
Motif: Ca2+ at (0,0,0); 2F- at (1/4,1/4,1/4) & (3/4,3/4,3/4)
4CaF2 in unit cell
Coordination: Ca 2+ 8 (cubic) : F? 4 (tetrahedral)
In the related Anti-Fluorite structure Cation and
Anion positions are reversed
Structures of Ionic Solids based on CCP
Fluorite structure CaF2 / {Na2O Anti-Fluorite}
6
Two Miscellaneous Structural Concepts
Isostructuralism
Minerals with the same structure, but different
compositions
CaF2 - BaCl2
Antistructuralism
Minerals with the same structure, but one has
cations where the other has anions and vice-versa
CaF2 - Na2O
The CaF2 (Fluorite) Structure
Can be thought of as a 3D
array of alternating empty
and occupied cubes
The CaF2 (Fluorite) Structure
ZnS Zinc Blende
(Sphalerite)
Structures of Ionic Solids Based on CCP
Locations of
Tetrahedral Holes
in FCC Structure
Cubic Zinc Sulfide
(Zincblende) Structure
(FCC S(0,0,0)，
Zn(?, ?, ?). Td group
(S atoms: cubic close packing，
Zn atoms fill in half of the
tetrahedral interstitials
Structures of Ionic Solids Based on CCP
ZnS Zinc Blende (Sphalerite)
CCP S2- with Zn2+ in half Tetrahedral holes (only
T+ {or T?} filled)
Lattice: FCC
4ZnS in unit cell
Motif: S at (0,0,0); Zn at (1/4,1/4,1/4)
Coordination: 4:4 (tetrahedral)
Cation and anion sites are topologically identical
7
Examples of Structure Adoption
NaCl (Halite)
Very common, Most alkali halides (CsCl, CsBr, CsI
excepted)
Most oxides / chalcogenides of alkaline earths
Many nitrides, carbides, hydrides (e.g. ZrN, TiC, NaH)
CaF2 (Fluorite)
Fluorides of large divalent cations, chlorides of Sr, Ba
Oxides of large quadrivalent cations (Zr, Hf, Ce, Th, U)
Na2O (Anti-Fluorite)
Oxides /chalcogenides of alkali metals
ZnS (Zinc Blende/Sphalerite)
Formed from Polarizing Cations (Cu+, Ag+, Cd2+, Ga3+...) and
Polarizable Anions (I?, S2-, P3-, ...);
e.g. Cu(F,Cl,Br,I), AgI, Zn(S,Se,Te), Ga(P,As), Hg(S,Se,Te)
Structures of Ionic Solids Based on CCP
Complex-ion Variants
Structures of Ionic Solids Based on CCP
Hexagonal Zinc
Sulfide (Wurtzite)
Structure
HCP S2- with Zn2+ in half Tetrahedral
holes (only T+ {or T?} filled)
Lattice: Hexagonal
Motif: 2S at (0,0,0) & (2/3,1/3,1/2); 2Zn
at (2/3,1/3,1/8) & (0,0,5/8)
2ZnS in unit cell
Coordination: 4:4 (tetrahedral)
C6v group
Structures of Ionic Solids based on HCP
ZnS Wurtzite
Structures of Ionic Solids Based on HCP
ZnS Wurtzite
Comparison of Wurtzite
and Zinc Blende
8
Some Semiconductors Structure
III- V group II- VI group
Compound Crystal
Structure
Lattice
Constant（ ?）
Compound Crystal
Structure
Lattice
Constant（ ?）
BN zincblende zincblende a=5.406
AlP zincblende a=4.462
ZnS
wurtzite a=3.821,
c=6.257
AlAs zincblende a=5.662 ZnSe zincblende a= 5.667
AlSb zincblende a=6.136 zincblende a=6.101
zincblende a=4.100
ZnTe
wurtzite a=3.814,c=6.257 GaN
wurtzite a=3.18,c=5.17 zincblende a=5.818
GaP zincblende a=5.451
CdS
wurtzite a=4.136
c=6.713
GaAs zincblende a=5.653 CdSe wurtzite a=4.299,
c=7.010
GaSb zincblende a=6.095 CdTe zincblende a=6.471
InP zincblende a=5.869 HgTe zincblende a=6.420
InAs zincblende a=6.058
InSb zincblende a=6.479
Descriptions of Structures
With CCP anion array:
Rock salt, NaCl O occupied
Zinc Blende, ZnS T+ (or T?) occupied
Antifluorite, Na2O T+ and T? occupied
With HCP anion array:
Wurtzite, ZnS T+ (or T?) occupied
With CCP cation array:
Fluorite, ZrO2 T+ and T?occupied
Very long sequences (~several hundred layers, say 500 ?
in the repeat unit) have been observed in some polytypic
materials (causing by screw dislocations).
The simplest Polytypism is
… ABAB… and … ABCABC… two polytypes
B
A
C
B
A
HCP CCP
Structure of Multicomponent Compound
Derived from Zincblende and Wurtzite
Zincblende Wurtzite
CuFeS2 CuSbS 2
AgGeTe2 CuFe2S3
Ordered
superlattice
Cu2SnFeS4 Cu3AsS4
MgGeP2 a-AgInS2
ZnSnAs2
Cu2GeS3
Disordered
Superlattice
Cu2SnTe3
Cu3SbS3
b-Cu2HgI4
b-Ag2HgI4
Ordered
Defected
Superlattice
In2CdSe4
CuSiP3 Al2ZnS4
a-Ag2HgI 4
a-Cu2HgI4
Disordered
Defected
Superlattice
Ga2HgTe4
Structure of CuFeS2 and ZnSnAs2
vCuFeS2： tetragonal system,
lattice constant c ≈ 2a
vZnSnAs2 exist as ordered
CuFeS2 structure at room
temperature, when temperature
increased, Zn and Sn array
disorderly, which make its
structure identical to cubic ZnS
structure。
vThese structures are called ZnS
derivative. They are ordered
superlattices.
Structures of Ionic Solids Based on HCP
NiAs
Nickel Arsenide
Coordination
HCP As with Ni in all Octahedral holes
Lattice: Hexagonal - P
a = b, c =(8/3)a
Motif: 2Ni at (0,0,0) & (0,0,1/2), 2As at (2/3,1/3,1/4) & (1/3,2/3,3/4)
2NiAs in unit cell
Coordination: Ni 6 (octahedral) : As 6 (trigonalprismatic)
9
An alternative unit cell origin
is at As (rather than Ni)
NiAs (Nickel Arsenide)
HCP As with Ni in all Octahedral holes
Lattice: Hexagonal - P
a = b, c =8/3a
Motif: 2Ni at (0,0,0) & (0,0,1/2)
2As at (2/3,1/3,1/4) & (1/3,2/3,3/4)
2NiAs in unit cell
Coordination: Ni 6 (octahedral) : As 6 (trigonalprismatic)
vLattice Constant: a=3.602 ?, c=5.009 ?
vThe coordination of Ni and As is 6， but their structures
are different： Ni fill in the octahedronal coordination from
the hcp of As, and As exist in the trigonal prism of Ni.
vIn NiAs structure, the neighboring octahedra of Ni atoms
share face. The distance of Ni-Ni is only 2.50 ?， close to
that in metallic Ni, thus NiAs crystal shows obvious metallic.
Nickel Arsenide (NiAs) Structure
In the c-direction, the Ni-Ni
distance is rather short. Overlap of
3d orbital gives rise to metallic
bonding.
The NiAs structure is a common
structure in metallic compounds
made from (a) transition metals with
(b) heavy p-block elements such as
As, Sb, Bi, S, Se.
Coordination of As
is also 6 but as a
trigonal prism:
CdI2
Cadmium
Iodide
Structures of Ionic Solids Based on HCP
HCP I with Cd in Octahedral holes of alternate layers
Lattice: Hexagonal - P
Motif: Cd at (0,0,0);
2I at (2/3,1/3,1/4) & (1/3,2/3,3/4)
1CdI2 in unit cell
Coordination: Cd - 6 (Octahedral) :
I - 3 (base pyramid)
CdI2
Cadmium
Iodide
Structures of Ionic Solids Based on HCP
HCP I with Cd in Octahedral holes of alternate layers
A c B A c B……
Polyhedral representation is most useful using CdI6
octahedra (compare with NiAs)
CdI2 Cadmium Iodide
Structures of Ionic Solids Based on HCP
CdI2 structure: CaI2,Ca(OH)2, MgBr2,MgI2, Mg(OH)2,
Cd(OH)2, MnI2, Mn(OH)2, Fe(OH)2, CoBr2,TiS2, ZrS2, SnS2,
TiTe2, Ni(OH)2
10
Structures of Ionic Solids Based on HCP
Rutile Structure
HCP anion lattice ? ?
Octahedral holes occupied
Arises from the preference of
Ti for octahedral coordination
(6,3) Coordination
TiO6 –octahedra
OTi3 –trigonalplanar
Rutile: ceramic pigment (white color)
Rutile (TiO2) Structure
O2- ions are in HCP.
TiO6 are in corner-sharing along a and b
directions; in edge-sharing along c direction
Crystal system:tetragonal
Unit cell dimensions: a=4.5937 ?; c=2.9587 ?
Rutile Crystal Structure
Ti4+： 000， ? ? ?
O2-: uu0, (1-u)(1-u)0, (?+u)(?-u)
?, (?-u)(?+u) ?, u=0.31
Compounds with the same
structures: GeO2、 SnO2、 PbO2、
MnO2、 MoO2、 NbO2、 WO2、
CoO2、 MnF2 and MgF2 etc．
Anatase (TiO2) Structure
O2- ions are in CCP.
TiO6 are all in edge-
sharing .
Crystal system:
tetragonal
Unit cell dimensions
a = 3.7845 ?
c = 9.5143 ?
Structures of Ionic Solids
Some other ionic solid structures
Spinel –? named for the mineral MgAl2O4 –? general
formula AB2O4
FCC array of O2- ions
?A cations occupy 1/8 of T holes
?B cations occupy ? of O holes
?Sometimes denoted A[B2]O4
?Square brackets indicate
species occupying O holes
?Characteristic of some d-block
oxides
?Fe3O4, Co3O4, Mn3O4
Spinel Structure
11
fcc array of O2- ions, Mg2+
occupies 1/8 of the tetrahedral
and Al3+ occupies 1/2 of the
octahedral holes
→ normal spinel:
AB2O4
→ inverse spinel:
B[AB]O4 (Fe3O4):
Fe3+[Fe2+Fe3+]O4
The Spinel structure: MgAl2O4 Spinel and Inverse Spinel
AB2X4 – after MgAl2O4
X most commonly O
A2+, B3+
CCP array of O2- with
1/8 of tetrahedral holes
occupied by A2+ and
half of the octahedral
holes occupied by B3+
Unit cell contains
eight formula units
In inverse spinel half of
the B3+ ions occupy 1/8
tetrahedral holes and ?
of octahedral holes sites
are occupied by A2+ ions,
another ? of octahedral
holes sites are occupied
by the other half of B3+
ions
At least one of the
metals is d-block
CoFe2O4 has inverse
spinel structure
Some Non-close Packed Ionic Solid Structures
Cesium Chloride
CsCl, CsBr, CsI, NH4Cl
Cubic unit cell
§Anions at vertices
§Can model as vice-versa
§CN=8 for cation and anion
§(8,8) packing
CsCl Crystal Structures
Cl?:Primitive Cubic lattice
Cs+ fill in the cubic interstitials
The coordination number of both
the anion and cation are 8
Structures of Ionic Solids
Some non-close packed ionic solid structures
MoS2 Molybdenite
Unit cellBa B Ab A… ..
MoS2 Molybdenite
Hexagonal layers of S atoms are NOT Close-packed
in 3D
Lattice: Hexagonal - P
Motif: 2Mo at (2/3,1/3,3/4) & (1/3,2/3,1/4)
4S at (2/3,1/3,1/8), (2/3,1/3,3/8), (1/3,2/3,5/8) & (1/3,2/3,7/8)
2MoS2 in unit cell
Coordination: Mo 6 (Trigonal Prismatic)
S 3 (base pyramid)
12
Structures of Ionic Solids
MoS2 vs CdI2
both MoS2 and CdI2 are
LAYER structures
MoS2 layers are edge-
linked MoS6 trigonal
prisms
CdI2 layers are edge-
linked CdI6 octahedra
Lattice: Primitive Cubic
1ReO3 per unit cell
Motif: Re at(0,0,0);3O at (1/2,0,0), (0,1/2,0), (0,0,1/2)
Re: 6 (octahedral coordination)
O: 2 (linear coordination)
ReO6 octahedra share only vertices
Examples:
WO3 , AlF3 , ScF3 , FeF3 ,
CoF3 , Sc(OH)3 (distorted)
Perovskite Structure (CaTiO3)
BaTiO3, SrFeO3, NaNbO3, KMgF 3, KZnF3
Perovskite Structure
ABO3 e.g. KNbO3,, SrTiO3, LaMnO3
SrTiO3 cubic, a=3.91 ?
In SrTiO3, Ti-O=a/2=1.955 ?
Sr-O=a√2/2=2.765 ?
CN of A=12, CN of B=6
OR
13
Perovskite Structure
Many ABX3 materials
adopt
perovskite structure
?Piezoelectrics
?Ferroelectrics
Cubic structure
?A = 12 coordinate in X
?B = 6 Coordinate in X
Perovskite ?? an Inorganic Chameleon
ABX3 - three compositional variables, A, B and X
CaTiO3 ?dielectric
BaTiO3 ? ferroelectric
Pb(Mg1/3Nb2/3)O3 ?
ferroelectric
Pb(Zr1-xTix)O3 ?
piezoelectric
(Ba1-xLax)TiO3 ?
semiconductor
(Y1/3Ba2/3)CuO3-x ?
superconductor
NaxWO3 ? mixed
conductor;
electrochromic
SrCeO3 ? H - protonic
conductor
RECoO3-x ? mixed
conductor
(Li0.5-3xLa0.5+x)TiO3 ?
lithium ion conductor
LaMnO3-x ? Giant
magneto- resistance
TiO6 –octahedra
CaO12 –cuboctahedra
(Ca2+ and O2- form a cubic
close packing)
→ preferred basis structure of
piezoelectric, ferroelectric and
superconducting materials
The Perovskite Structure CaTiO3 Lattice: Primitive Cubic (idealized structure)
1CaTiO3 per unit cell
A-Cell Motif: Ti at (0, 0, 0); Ca at (1/2, 1/2, 1/2); 3O at (1/2, 0,
0), (0, 1/2, 0), (0, 0, 1/2)
Ca 12-coordinate by O (cuboctahedral)
Ti 6-coordinate by O (octahedral)
O distorted octahedral (4xCa + 2xTi)
TiO6 octahedra share only vertices
CaO12 cuboctahedra share faces
Examples: NaNbO3 , BaTiO3 , CaZrO3 , YAlO3 , KMgF3
Many undergo small distortions: e.g. BaTiO3 is
ferroelectric
The Perovskite Structure, ABO3
14
The Atom Positions in
Perovskite Structures
If cation and anion keep contact, then
But in fact, only need to satisfy：
t is called tolerance coefficient.
Ideal perovskite is cubic system, but
many perovskites have been distorted
to tetragonal, orthorhombic and
monoclinic systems.
)RR(2)RR( XBXA +=+
1t7.0
),RR(2t)RR( XBXA
<<
+=+
Connected Polyhedra (for larger structural units)
common vertex
Corner-sharing edge-sharing
A dimeric unit of vertex-shared tetrahedra
bitetrahedra common edge
bioctahedra
face-sharing
Polyhedral Linking
The stability of structures with different types of
polyhedral linking is vertex-sharing > edge-sharing >
face-sharing
effect is largest for cations with high charge and
low coordination number
especially large when r+/r- approaches the lower
limit of the polyhedral stability
Rhenium Trioxide (ReO3)
and Tungsten Bronzes
ReO3: corner-sharing ReO6 octahedra
Empty body center (No Sr)
UO3, MoF3
3D network of open channels
NaxWVxWVI 1-xO3
Some body centers occupied by Na (0 ≤ x
≤ 1)
Low x: pale yellow, semiconducting
High x: metallic (“bronzes”)
The Wide World of WO3
Unit cell contents:
W6+: 8×(1/8) = 1
O2-: 12×(1/4) = 3
WO3, tunable properties and adaptive structure
Void space for injection of H+ or Li+ or Na+ + e-→
Hx1+WxVW1-xVIO3 “Tungsten Bronzes”
Electrochromic properties: pH-electrodes, displays,
ion-selective electrodes, batteries, sensors
Electrochemical or chemical synthesis of MxWO3
WVI, Oh O2- Another Way to View WO3
O2- on face centers
W6+ in body center
15
Polymorphs of WO3??Hexagonal
Tungsten Bronzes (HTB)
AxWO3, A=K, Rb , Tl, Cs, In
Still chains of corner-sharing WO6
Oh along c-axis
Larger channels to accommodate
larger A
A cations reside in hexagonal
channels
0.19 < x < 0.33
x < 0.19: Mix of WO3 and HTB,
regularly spaced
Hexagonal Tungsten Bronze
(HTB)
Hexagonal
Tunnel
Injection of
larger M+
than in cubic
WO3
Vertex-sharing
WO6
Polymorphs of WO3 ? Tetragonal
Tungsten Bronzes (TTB)
AxWO3, A = Na, K, In, Ba , Pb
Still chains of corner-sharing
WO6 Oh along c-axis
Perovskite-type square tunnels
Triangular tunnels, as in HTB
Pentagonal tunnels, mixture of
one 90°, four 120°
The Layered Structure of MoO3
=
Chains of
corner-sharing
ReO6 octahedra:
Each chains shares
square place edges
with two other chains
Interlamellar
space, van der
Waal gap
Topotactic Reaction of MoO3
Topotactic insertion: MoO3 remains intact
Hydrogen insertion
MoO3 HxMoO3
0 ≤ x ≤ 2
Four phases:
0.23 < x < 0.4 Blue Orthorhombic
0.85 < x < 1.04 Blue Monoclinic
1.55 < x < 1.72 Red Monoclinic
x = 2.00 Green Monoclinic
Powder XRD, ND: change of crystal class, but layer
integrity is maintained
?Protons are mobile
H+, e-
Aqueous
HxMoO3, A Proton Conductor
?1D proton conductivity, single protonation H0.3MoO3
?Then between layers for larger values of x
Mo MoMo
O O
H
Mo MoMo
O O
H H
Low H-Loadings: 1-D
proton conductor
along chains
High H-Loadings:
saturation and protons
jump to adjacent layer
Mo MoMo
O O
H H H1.7MoO3, double-
protonation
more mobile protons
Alternate Side-
View of One Layer
16
Electrochromic WO3 Thin
Films for Smart Windows
Electrochromic Film:
Multilayer stacks that behave
like batteries
Visible indication of their
electrical charge
Fully charged: opaque
Partially charged: partially
transparent
Fully discharged: transparent
Uses: mirrors, displays,
rechargeable solid state batteries,
pH-sensitive electrochemical
transistors or displays, chemical
sensors, solar cells, selective
oxidation catalyst, …
e- into
Conducting
Bond of WVIO3
M+ into hole
Chemical Vapor Deposition onto
substrate:
2WF6 + 3O2 → 2WO3 + 6F2
2W(CO)6 + 9O2 → 2WO3 + 12CO2
Electrochromic glass is an energy-saving component for buildings
that can change color on command. It works by passing low-voltage
electrical charges across a microscopically-thin coating on the glass
surface, activating aelectrochromic layer which changes color from
clear to dark. The electric current can be activated manually or by
sensors which react to light intensity. Glass darkening reduces
solar transmission into the building. When there is little sunlight,
the glass brightens, so that the need for the artificial light is
minimized.
Electrochromic Glass
OFF ON
Electrochemical Injection of M+, e-
M+ into hole
e- into Conducting
Bond of WVIO3
WO3: Transparent
Ax1+WxVW1-xVIO3: Color ∝ A, x
? A+ = H+, Li+ or Na+, 0 ≤ x ≤ 1
? Absorption of light ∝[A+]
Why the Color Change?
WO3
Wide band
gap insulator
MxWO3
Narrow band gap
semiconductor
x(M+ + e-) M
xWO3
Metallic
x(M+ + e-)
VB
[O2-(2ppi)]
CB
[W6+(d0)]
Localized VB
[W5+(d1)]
Delocalized
VB [W5+(d1)]
W5+ + W6+ fi W6+ + W5+
Layered Materials and
Intercalation Chemistry
Low-dimensionality materials: clusters, chains,
layers
Two-dimensionally extended, covalently bonded
layers
Layers interact non-covalently in the third
dimension (electrostatic, hydrogen-bonded and/or
van der Waals)
Directly or with interlayer species
Metal dichalcogenides, metal phosphonates, metal
oxides
Layered MoO3, a proton conductor
Transition Metal Dichalcogenides
Layered metal dichalcogenide
hcp layers of S2-
Ti4+ sandwiched between alternate S2- layers
Oh or D3h metal sites, depends on M
Strong intralayer MS2 covalent bonds
Weak interlayer vander Waals forces between TiS2 layers
hcp S2-
Ti4+ in D3h site
van der Waals gap
S
S
Ti
S
S
Ti
S
S
Ti
17
Transition Metal Dichalcogenides
Group IV,V,VI metals
Ti V Cr
Zr Nb Mo
Hf Ta W
Group VI chalcogens
S, Se, Te
(or mixed, eg S2-xSex)
Trigonal
Prismatic
Site
D3h
S
Ti
SS
S
SS
Intercalation of MS2
S
S
Ti
S
S
Ti
S
S
Ti
Li
Li
Intercalation: Inserting atoms, ions, clusters, etc. into an
interlamellar space, with minimal perturbation of host
structure
Electrochemical intercalation
Chemical intercalation:
xC4H9Li + TiS2 LixTiS2 + (x/2)C8H18 (0 ≤ x ≤ 1)Hexane
N2, RT
Filter, hexane wash
Li+ intercalated in vander Waals
gap, with increase in layer
separation (~10%), e? injected into
Conducting Bond of TiS2
Molybdenum Sulfide (Molybdenite)
Mo is 6 coordinate
S is 3 coordinate
Two Dimensional Material (TDM)
Intercalation
Exfoliation
TDM
10 15 20 25 30 35 40 45 50 55 60 65 70 75
2 Theta
Intensity
TDM
Bulk MoS2
TDM XRD compared
to Bulk MoS2:
TDM Properties
Corrosion resistant
Barrier to impurities and moisture
Semi-conducting to semi-metallic
Self-assembling
Encapsulates many impurities
Catalytic for sulfur conversion
TDM Applications
Hydrogen Storage Materials
Metal Hydride Batteries
Desulfurization Catalysts
Water Treatment
Nanocomposite materials
Anode: xLi→ xLi+ + xe-
Cathode:TiS2+xLi++xe- → LixTiS2
Cell:Ti4+S2+xLi=Lix+Ti1-x4+Tix3+S2
?Open circuit voltage, 2.5V
?High Density Light Weight
Rechargeable Batteries
Electrochemical Intercalation of
TiS2 for Battery Applications
TiS2
Cathode Li(s)AnodeLi+
e -
Non Aqueous Solvent
(Dioxane) + LiClO4
or glassy
PEO8LiSO3CF3
18
Silicates
More than 90% of the minerals in Earth’s crust are
members of a mineral family called silicates.
These are compounds of elements silicon and oxygen,
plus one or more metallic element, such as
aluminum or iron.
The unit is held together by covalent bonds between
the silicon atom and oxygen atoms. If the imaginary
lines are drawn to connect the centers of the four
oxygen atoms, they make a geometric figure called a
tetrahedron. Because the silicon atom is in the
center, it’s known as the silica tetrahedron.
Anion in Borate Crystal Structures
vIsland complex anion：
(a) [BO3]3- triangle
(b) [B2O5]4- bi-triangle
(C) [BO4]5- tetrahedra
vRingy complex anion：
(d) [B3O6]3-
(e) [B3O3(OH)4]-
(f) [B3O3(OH)5]2-
(g) [B4O5(OH)4]2-
Composed mainly of silicon and oxygen, two
most abundant elements in earth ’s crust (rocks,
soils, clays, sand)
Basic building block: SiO44- tetrahedron
Si-O bonding is largely covalent, but overall
SiO4 block has charge of –4
Various silicate structures – different ways to
arrange SiO44- blocks
Silicate Ceramics 3-D Silicate (Quartz)
Why is it called SiO2?
OO
OO
Si
OO
O
Si
OO
O
Si
O
OO
Si
O
OO
Si
Oxygens are shared between adjacent tetrahedra
4 x 1/2 O = 2
A diamond network of Si
atoms with O inserted within
each network linkage
Every oxygen atom is shared by adjacent tetrahedra
Silica can be crystalline (e.g., quartz) or amorphous, as
in glass (fused or vitreous silica)
Silica = Silicon Dioxide = SiO2
3D network of SiO4 tetrahedra in cristobalite
High melting temperature of 1710°C
β-Cristobalite Structure (SiO2)
Silicate Properties
All silicates are made of the same general
elements: metallic ions bound to silicate
ions that are arranged in different
structures
The properties of the minerals are
controlled by the silicate structures.
19
Silicate Properties: “Island Silicates”
No shared oxygens; “independent”tetrahedra.
Example: olivine (Mg, Fe)2SiO4
No cleavage –same bond strength in all
directions.
Structures of Silicate Minerals
Island Structure
Silicate Properties: “Single-chain Silicates”
Some shared oxygens, creating a single chain.
Example: pyroxene (Mg,Fe)2Si2O6
Pyroxene is commonly black or dark green.
Single-chain silicates have cleavage parallel to the
chains:
Weak bonds between the chains.
à2 planes of cleavage at 90° to each other.
Structures of Silicate Minerals
Chain-like Structure
Silicate Properties: “Double-chain Silicates”
? More shared oxygens, creating a double chain.
? Example: amphibole (Ca, Fe, Mg, OH)-silicate.
? Amphibole is commonly black and is hydrous (hence
the OH).
? Double-chain silicates have cleavage parallel to the
chains:
?Double chains
?à2 planes of cleavage at 60° and 120°
Silicate Properties: “Sheet Silicates”
Even more shared oxygens, linked indefinitely in all
directions forming sheets.
Examples: micas
Biotite (dark) (K, Mg, Fe, Al, OH)-silicate
Muscovite (light) (K, Al, OH)-silicate
Perfect cleavage along planes (basal). You can peel these
minerals apart like pages.
20
Structures of Silicate Minerals
Layer Structure
Silicate Properties: “Framework Silicates”
All oxygens are shared, linked in an infinite 3D
network.
Example: quartz SiO2
Strong bonding in all directions àno cleavage.
Example: feldspar (Ca, Na, K)AlSi3O8
Most abundant minerals on earth.
White to pink to gray
Two good cleavages at 90° to each other.
Structures of Silicate Minerals
Framework Structure
Silicate Minerals
Silicate anion (SiO44-)
Other minerals containing silicate anion:
Zircon (ZrSiO4)
Garnets (M2+)3(M3+ )2(SiO4)3
M2+ = Ca2+, Mg2+, or Fe2+
M3+ = Al3+, Cr3+,or Fe3+
Topaz Al2SiO4(F,OH)2
Aluminosilicates
OO
O
Al
OO
OO
Si
OO
OO
Si
OO
OO
Si
OO -
OO
Si
M+
really covalent structures, but may be helpful to think of
O2-, Si4+ , and Al3+ ions
Replacement of some Si+4 with Al+3
Charge neutrality must be maintained by adding cations
3-D Aluminosilicates
(i.e. zeolites)
contain channels that can
trap molecules for
reactions or for separation
ZSM-5 Zeolite Catalyst:
Alkylation and
aromatization of
hydrocarbons
21
Zeolites
Open framework silicates or
aluminosilicateswith ion-exchange
properties
Mn+x/n[(AlO2)x(SiO2)y]x-?mH2O
Fraction (x/(x+y)) of Si sites substituted
for Al
Corner-sharing TO4 tetrahedra, T = Al
or Si
No adjacent Al tetrahedra ? Al:Si = 0
to 1 limit
Structures drawn with polyhedra or
lines connecting metal centers, ignoring
doubly-bridging oxygens
Zeolite Y: α-cage, connected by 12-ring
windows
Hydrothermal Synthesis of Zeolites
NaAl(OH)4(aq) + Na 2SiO3(aq) + NaOH(aq)
25°C, Condensation polymerization
Naa(AlO2)b(SiO2)c?H2O, Gel
25 to 250°C, Gel ordering,
Nucleation site formation and growth,
autogenous P
Nax(AlO2)x(SiO2)y?zH2O crystals
Open inorganic framework
One-, two - or three-dimensional networks of interconnected
channels
Channels connect through “windows”to define interior cavities
Window size determines maximum size of molecule that can enter
zeolite
Extraframework
cations
Charge balancing,
void-filling
(up to 50%),
structure-
stabilizing,
ion-exchangeable
Equal ratio to Al
AlIIIO4, Td
Each oxygen
shared with
another metal
center
(AlO2)-,
introduces
negative
charge
Si IVO4, Td
Each oxygen
shared with
another metal
center
(SiO2), neutral
Occluded
water
Easily removed
by heating
under vacuum,
25 to 500°C
What’s in a Name: Nax(AlO2)x(SiO2)y?zH2O Porous Materials
Name Pore Size Domain
Microporous 5 to 20 ?
Mesoporous 20 to 500 ?
Macroporous > 500 ?
?Crystalline or non-crystalline
?Metastable, require soft chemistry methods:
crystallization from gels most common
?Applications: size/shape discrimination for catalysis,
ion-exchange, separation, sensing, host-guest inclusion
chemistry, optical materials, magnetic materials
?Microporous, crystalline: molecular sieves
?Zeolites = aluminosilicate or silicate molecular sieves
Zeolites
§1756 - Boiling (zeo) stones (lithos)
§Crystalline aluminosilicates
containing well-defined channels
and cavities < 20 ?
§Enormous variety in chemical
composition and structure
§Tremendous Industrial Applications:
Ion Exchangers –Water Softeners
Molecular Sieves & Sorbents
Catalysts
Zeolite Structure
Primary building blocks are [SiO4]-4 and [AlO4]-5
tetrahedra linked by corner sharing oxygens
Approximately 40 naturally occurring zeolites have been
characterized and more than 130 zeolites have been
synthesized!!
SiAl
Al
O O
Si
Si
O
Si
O
Al
O
Si
O
Zeolite A
(LTA)
22
Zeolite Chemistry
General formula for the composition of a zeolite is
Mx/n[(AlO2)x(SiO2)y]? mH2O
where cations M of valence n neutralize the
negatively charged zeolite framework.
SiO2 tetrahedra are electrically neutral (e.g., quartz)
Substitution of Si(IV) by Al(III) creates an electrical
imbalance and neutrality is provided by an
exchangeable cation
Al
Si
Na + Na +
Acid Sites
Zeolite as
synthesized
Br?nsted acid form
Lewis acid form
Na+ Na+
H+ H+
+H2O -H2O (500°C)
+
