Download important structure types

Important Structure Types
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L.Viciu| ACII| Imprtant structure types
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A. Structures derived from cubic close packed
1. NaCl- rock salt
2. CaF2 – fluorite/Na2O- antifluorite
3. diamond
4. ZnS- blende
B. Structures derived from hexagonal close packed
1. NiAs – nickel arsenide
2. ZnS – wurtzite
3. CdI2 – cadmium iodide
4. CdCl2 – cadmium chloride
C. Non close packed structures
1. CsCl – cesium chloride
2. MoS2 - molybdenite
D. Metal oxide structures
1. TiO2- rutile
2. ReO3 – rhenium trioxide
3. CaTiO3 – perovskite
4. MgAlO4 - Spinel
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Voids in f.c.c. structure
• O Oh sites in f.c.c. arrangement of
anions (fcc unit cell)
•4 Oh sites in total
• location:
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12  1( centre)  4
4 ( edge)
• T Td sites in the f.c.c . arrangement
of anions
•8 Td sites in total
•Location: on the body diagonals – two
on each body diagonal at ¼ of the
distance from each end.
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A-1. Rock salt: NaCl (halite), Sp. Group, Fm-3m
Ionic structure
rCl   1.81
rNa  0.95
rNa
rCl 
Cl-
Red balls are
Purple balls are Na+
Edge shared Oh
 0.52 
Na  Oh coordinate d
Cl- form the c.c.p. array
Na+ fills all the Oh holes while the Td holes are empty
Na+: 8x1/8+6x ½= 4
Cl-: 12x ¼ +1=4
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 4 NaCl per unit cell
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Compounds with NaCl-rock salt structure
• Halides: LiX, NaX, KX, RbX, AgX –except AgI
• Oxides: MgO, CaO, SrO, BaO, TiO, MnO, FeO, CoO
• Chalcogenides: MgS, CaS, MnS, MgSe, CaSe, CaTe,
At room temperature, they are electrical insulators and transparent in
the visible spectral region.
At elevated temperatures, they could become ionic conductors, with
the major contribution to charge transport from positive ion vacancy
motion.
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A-2. CaF2-fluorite/Na2O antiflorite (Fm-3m)
Ionic compound
I. Ca2+ ions form the c.c.p. array
F- fills all Td voids (Oh voids are empty)
Ca2+: 8 x 1/8 + 6 x ½ = 4
F-: 8 x 1=8
Edge shared FCa4 Td
II. F- ions form a simple cubic array
Ca2+ – in the ½ of the cubic sites
F-: 8 x 1/8 +12 x ¼ + 6x ½ +1= 8
Ca2+: 4 x 1 = 4
 4 CaF2 in the unit cell
 C.N.: Ca-8(cubic): F-4(Td)
Corner shared CaF8 cubes
In the Anti-Fluorite (Na2O) structure, Cation and Anion positions are reversed!
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Compounds with CaF2 (fluorite) and Na2O
(antifluorite) structure:
• Fluorite:
Halides: SrF2, SrCl2, BaF2, BaCl2, CdF2, HgF2
Oxides: PbO2, CeO2, PrO2,ThO2
• Antifluorite:
Oxides: Li2O, Na2O, K2O, Rb2O
Chalcogenides: Li2S, Li2Se, Na2S,
Na2Se, Na2Te, K2S, K2Se, K2Te
 Compounds with fluorite structure are ionic conductors: the charge is carried by
anions
 The fluorite structure favors anion motion because the anions have less charge
and are closer together than the cations
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Fluorite type compounds: Fast Ionic Conductors
ZrO2 stabilized with CaO or Y2O3: conduction through O2-
High mobility of anion vacancies gives rise to fast ionic (anionic)
conduction in fluorite type structure.
Batteries = energy conversion + energy
storage
Solid oxide fuel cells = energy
conversion
http://www.gepower.com/research/seca/sofc_research.htm
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A-3. Diamond Structure
Covalent structure: the directionality of the covalent bonds dictates
the crystal structure.
C- hybridized sp3
½ of the C form the c.c.p. array
½ of C fills ½ of the Td voids (Oh voids
½
¾
are empty)
½
C: 8 x 1/8+6 x ½ = 4
¼
0,1
¼
0,1
¾
C: 4 x 1 = 4
C.N.: 4
The most stable covalent structure
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Properties of diamond
•High pressure allotrope of C (graphite  diamond @80kbars)
•Insulator (Eg = 5.4 eV) and transparent; color in diamonds originates
from impurities
i.e. colored diamond:
• good thermal conductivity
i.e. used in semiconductors industry to prevent them from
overheating (thermal sink)
• high refractive index and high optical dispersion(shine)
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Compounds with diamond like structure
Group 4 of elements: Si, Ge and -Sn
radius
Lattice
constant (Å)
Melting
Conductor?
Point (ºC)
Eg(eV)
Carbon diamond
3.56
3550
Insulator
5.4
Silicon
5.43
1410
Semiconductor
1.1
Germanium
5.66
940
Semiconductor
0.7
-Tin
6.49
230
Zero gap
semiconductor
0
All have the cubic structures (space group: Fd-3m)
Eg is inverse proportional with the bond lengths
Longer bonds are weaker and the electrons are easily liberated  small band gaps
-Tin is the largest in the group  weakest bonds (larger unit cell)
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Changing the motif in diamond structure
diamond
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Zinc Blende
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A-4. ZnS- Zinc Blende (Sphalerite)
Similar with diamond structure
A
Red spheres – S2Green spheres – Zn2+
•S2-
Corner shared ZnS4 Td
Layers of ZnS4 Td stacked
..ABCABC..
form the c.c.p. array
•Zn2+ fills ½ of the Td voids (Oh voids are empty)
•S: 8 x 1/8+6 x ½ = 4
•Zn: 4 x 1 = 4
•C.N.: 4
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The crystal may be thought of as two interpenetrating
fcc lattices, one for sulfur the other for zinc, with their
origins displaced by one quarter of a body diagonal.
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Compounds with Zinc Blende- type structure
•
•
•
•
CuF, CuCl, -CuBr, -CuI, -AgI This small cation structure is found for small
metallic elements, which tend to form
-MnS red, -MnSe, BeS, , ZnS, strong sp3 covalent bonds.
-SiC, BN, BP
III-V compounds: GaP, GaAs, GaSb, InP, InAs, InSb
Note: Crystals containing tetrahedral groups are often piezoelectric (a
Td symmetry doesn’t have an inversion center).
i.e. Zinc blende is piezoelectric
Unstressed ZnS4 Td
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Stressed ZnS4 Td
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 Most semiconductors of commercial importance are isomorphous
with diamond and zinc blende
 Structure – electronic properties relations important for evaluating:
Band gap
Mobility
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Band Gap (Eg)
 ~ e
 Eg / kT
-conductivity
-mobility
Eg-Band gap
T- temperature
K-Boltzman constant
Eg increases with increasing the
electronegativity difference between
constituent ions.
Generally, band gap and transparency are
interconnected
Band gap generally increases with ionicity
 Band gap increases with ionicity
 Covalent semiconductors have narrow Eg
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Mobility () for rock salt and zinc blende type materials
Electronegativity difference 
 ~ e
 Eg / kT
In materials free of defects, the mobility is
determined by the effective mass interaction
with lattice vibration
1.
Mobility  as the molecular weight 
(heavy mass gives low scattering)
Compounds with ionic bonding
have low electron mobility
2.
Mobility  as the electronegativity difference btw ions (polarization effect
of mobile electrons or holes on the surrounding atoms)
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Typical Semiconductors
Silicon
GaAs
Diamond Cubic Structure
ZnS (Zinc Blende) Structure
4 atoms at (0,0,0)+ FCC translations
4 Ga atoms at (0,0,0)+ FCC translations
4 atoms at (¼,¼,¼)+FCC translations
4 As atoms at (¼,¼,¼)+FCC translations
Bonding: covalent
Bonding: covalent, partially ionic
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Properties
GaAs
Si
Crystal structure
zinc blende
diamond
Lattice constant
5.6532
5.43095
Band gap (eV) at 300 K
1.424 (direct)
1.12 (indirect)
Mobility (cm2/V.s)
8500
1500
Intrinsic carrier conc. (cm-3)
1.79x106
1.45x1010
Difficulty in growing stoichiometric GaAs crystals due to the loss of arsenic
evaporation (>600ᵒ); also the crystals are very brittle
crystal perfection and purity in silicon has reached levels never achieved with any
other synthetic materials.
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• Why semiconductors have diamond or ZnS –blende
structure?
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• Why semiconductors have diamond or ZnS –blende
structure?
Due to the covalent character of its bonding interaction
(the lattice is always composed of those elements with the
smallest difference in electronegativity).
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Structural Changing
pressure
Graphite 

 Diamond
pressure
Zinc blende  type : InAs , CdS , CdSe 

 NaCl  type
Graphite : C.N.= 3; dC-C = 1.415Å; =2.26g/cm3
Diamond: C.N. = 4 dC-C = 1.54Å;  = 3.51g/cm3
U. Müller-Inorganic Structural Chemistry
• Pressure –coordination rule: “with increasing pressure an increase of
the coordination number takes place”
• Pressure-distance paradox: “when the coordination number increases
according to the previous rule, the interatomic distances also
increases”
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Voids in f.c.c. structure
• O Oh sites in f.c.c. arrangement of
anions (fcc unit cell)
•4 Oh sites in total
• location:
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12  1( centre)  4
4 ( edge)
• T Td sites in the f.c.c . arrangement
of anions
•8 Td sites in total
•Location: on the body diagonals – two
on each body diagonal at ¼ of the
distance from each end.
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Filling voids in c.c.p. structures
CaF2
ZnS
all Td
½ Td
NaCl
Li3Bi
½ Td
c.c.p.
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all Oh
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all Td and all Oh
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Ulrich
Müller:
“Inorganic
structural
chemistry”
 all Td sites filled
 ½ of the Td sites filled
 ¼ of the Td sites filled
Fig. 128/pag203
“Relationships among the structures of CaF2, PbO, PtS, ZnS, HgI2, SiS2, and α-ZnCl2. In the top row all
tetrahedral interstices (= centers of the octants of the cube) are occupied. Every arrow designates a step in
which the number of =occupied tetrahedral interstices is halved; this includes a doubling of the unit cells in
the bottom row. Light hatching = metal atoms, dark hatching = non-metal atoms. The atoms given first in
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the formulas
form the cubic closest-packing”
A. Structures derived from cubic close packed
1.
2.
3.
4.
NaCl- rock salt
CaF2 – fluorite/Na2O- antifluorite
diamond
ZnS- blende
B. Structures derived from hexagonal close packed
1. ZnS – wurtzite
2. NiAs – nickel arsenide
3. CdI2 – cadmium iodide
C. Non close packed structures
1. CsCl – cesium chloride
2. MoS2 - molybdenite
D. Metal oxide structures
1. TiO2- rutile
2. ReO3 – rhenium trioxide
3. CaTiO3 – perovskite
4. MgAlO4 - Spinel
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Voids in h.c.p. structure
A
The spacing of the close packed
layers:
d = √8r/√3 = 1.633r
2 1 1
( , , )
3 3 2
B
c=2x1.633r=2x1.633xa/2=1.633a
c/a=1.633
A
The voids are identical to the ones found in FCC
(1/3, 2/3, 3/4)
(0,0,5/8), (⅔,⅓,7/8)
B
(0,0,3/8)
A
(1/
2
3, /3,
¼)
Oh void
(⅔, ⅓,1/8),
Td void
Octahedral voids occur in 1 orientation, tetrahedral voids occur in 2 orientations
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B-1. Wurtzite (ZnS) (P63mc)
A
B
A
S2--yellow spheres
Zn2+-green spheres
•S2- form the h.c.p. array (c/a=1.633)
•Layers of ZnS4 Td stacked ..ABAB…
•Alternate layers are rotated by 180ᵒ
about c axis relative to each other.
•Zn2+ fills ½ of Td voids (T+ or T-)
•S: at (0,0,0) and (2/3, 1/3, ½)
•Zn-: at (2/3, 1/3, 1/8) and (0,0, 5/8)
•c/a = 1.636 (the ideal c/a=1.633)
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Zn neighbors in Wurtzite structure
1
S2--yellow spheres
Zn2+-green spheres
nearest neighbors: 4 S ions
Next nearest neighbors: 12 Zn ions
(ex: the ion 1 has 6 Zn ions at distance a in the same plane with it and three Zn in the
plane below and then three in the plane above it –the next cell)
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Two unit cells of the Wurtzite structure
(0,0,0)
(1/3, 2/3, 3/8)
(0,0, 5/8)
(1/3, 2/3 ,0)
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Different view of the Wurtzite structure
•Zn-: 2 x ½ + 1=2 per cell at (1/3, 2/3 ,0) + h.c.p translation (2/3, 1/3, ½)
•S: 2 x 1 = 2 per unit cell at (1/3, 2/3, 3/8) + h.c.p translation (2/3, 1/3, 7/8)
•2 ZnS per unit cell
•C.N.: 4:4 (Td)
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Compounds with wurtzite type structure
•
•
•
•
•
•
ZnO, ZnS, ZnSe, ZnTe
BeO
CdS, CdSe, MnS, MnSe
AgI
AlN, GaN, InN, TlN,
SiC
The highlighted blue compounds are piezoelectrics
The symmetry of the wurtzite type structure allows for a distortion
along the c axis  distorted Td
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Zinc Blende
vs.
Wurtzite
•Different electrostatic interaction between an atom and its third neighbors
(…ABCABC… VS …ABAB…);
•Covalent compounds with tendency towards lattice instability as ionicity increases
A
B
A
Zn is Td coordinated  corner
shared Td
Zn is Td coordinated corner shared Td but the
layers are rotated by 180ᵒ relative to each other
…ABCABC…
…ABAB…
 = 4.11g/cm3
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 = 3.98g/cm3
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Zn next nearest neighbors in zinc
blende structure
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Zinc Blende vs. Wurtzite
Covalent compounds with tendency towards lattice instability as ionicity increases
Wurtzite structure is more open
Wurtzite is more ionic than Zinc Blende: the lattice energy of wurtzite is larger than
that of zinc blende
i.e.
Awurtzite = 1.641
Azinc blende = 1.638
 m.p.
Eg
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(A = constant in the lattice energy formula which
depends on the crystal geometry. It is the sum of a
series of numbers representing the number of
nearest neighbors and their relative distance from a
given ion)
zinc blende
sublimes at t=1185C
3.68eV
wurtzite
1850C
3.911eV
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B2. NiAs- Nickel Arsenide(P63/mmc)
5, 7 and 8 are arsenic ions common to two Oh; •NiAs6 Oh share opposite faces 
chains of face sharing Oh along c
3 and 7 are arsenic ions common to two Oh
•Chains of edge shared Oh in the ab plane
• As form the h.c.p. array (c/a=1.391)
• Ni fills all Oh voids (all Td voids empty)
•2As at (0,0,0) and (1/3,2/3,1/2
•2Ni at (2/3,1/3,1/4) and (2/3,1/3,3/4)
•C.N.: Ni 6 (octahedral) : As 6 (trigonal prismatic)
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•Edge sharing AsNi6 trigonal prisms
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NiAs – alternative views
I.
II.
As
Ni
1/
As
3/
4
Ni
4
0, 1/2
1/
1/ 3/
4, 4
2
0,1
As
Ni
I.
Ni at the corners of the hexagonal cell.
One As is in the center of a hexagonal prism
formed by six Ni atoms.
The result is doubling of the repeat unit in
the c- direction. 2NiAs per unit cell (Z=2)
II. As’s form the hexagonal close packed sublattice, which is interpenetrated by a primitive
hexagonal sublattice of the metal (Ni) atoms.
Hexagonal layers of nickel alternating with hexagonal layers of arsenic.
Note: this is not a layered structure ; it is a tightly connected three
dimensional array!
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Compounds with NiAs type structure
The NiAs structure is a common structure in metallic compounds of
(a) transition metals with (b) heavy p-block elements (As, Sb, Bi, S, Se).
•Intermetallic compounds: NiSb, NiSn, FeSb, PtSn, MnAs, MnBi, PtBi
•Transition metals chalcogenides: NiS, NiSe, NiTe, FeS, FeSe, FeTe, CoS,
CoSe, CoTe, CrSe, CrTe, MnTe
Overlap of 3d orbitals gives rise to metallic bonding.
c/a < 1.633 due to metallic bonding on c direction
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Most NiAs type materials are metallic.
 Bond distance, dNi-Ni, in NiAs is 2.55Å
 Typical dNi-Ni is the the range 2.7-2.9 Å
Change at the Fermi surface with change in the bond distance  change in c/a ratio
as changing the electron count.
A.West: page 249
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NiAs
vs.
NaCl
B
A
A
C
B
B
A
A
Both structures have all the octahedral voids filled
AB compounds: appreciable metallic bond adopt NiAs structure type
appreciable ionic bond adopt NaCl structure type
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B3: CdI2: Cadmium Iodide (P-3m1)
B
A
B
A
• I form the h.c.p. array
• one Cd at (0,0,0);
• Cd2+ fills ½ of Oh voids
• Two I:
• Hexagonal lattice
Cd2+
I-
(2/3,1/3,1/4); (1/3,2/3,3/4)
•1CdI2 in the unit cell
C.N.: Cd - 6 (Octahedral) : I - 3 (base pyramid)
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Alternative views
¾
¼
0,1
C.N.:
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Cd  6 (Octahedral)
 6:3
I  3 (base pyramid)
Cd ion in the highlighted
sulfur unit cell
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Compounds with CdI2 structure
van der Waals attraction between neighboring iodine layers
The structure is stabilized by highly covalent interactions and large, polarizable
anions
•Iodides of moderately polarizing cations; bromides and chlorides of
strongly polarizing cations;
e.g. PbI2, FeBr2, VCl2
•Hydroxides of many divalent cations
e.g. (Mg,Ni)(OH)2
•Di-chalcogenides of many quadrivalent cations
e.g. TiS2, ZrSe2, CoTe2
Anisotropic properties due to the layered structure
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NiAs
Ni
Ni
Ni
Ni
Ni
As
Ni
Ni
As
Ni
Ni
¾
vs.
Ni
NiAs view on c
axis (top view)
CdI2
Cd
Cd
Cd
Cd
I
Ni
Ni
Cd
I
Cd
Cd
Cd
0, 1
0, ½ , 1
¾
¼
¼
CdI2 view on the c
axis (top view)
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CdI2
B
A
vs.
CdCl2 (R-3m)
B
A
C
B
B
A
A
B
C
A
B
A
hexagonal close packed anions
Cubic close packed anions
•2D hexagonal structures with different stacking in the 3rd direction
•Layers made of CdX6 octahedra
•Between layers only van der Waals interactions L.Viciu| ACII| Imprtant structure types
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Compounds with CdCl2 structure
Hexagonal structure with c.c.p. anion arrangement therefore not
h.c.p. derived!
•Chlorides of moderately polarizing cations
e.g. MgCl2, MnCl2
•Di-sulfides of quadrivalent cations
e.g. TaS2, NbS2
•Cs2O has the anti-cadmium chloride structure
Anisotropic properties due to the layered structure
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Filling voids in h.c.p. structures
½ Oh filled
½ Td filled
h.c.p. array
CdI2
ZnS
all Oh filled
all Td filled?

NiAs
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No!
48
A. Structures derived from cubic close packed:
1.
2.
3.
4.
NaCl- rock salt
CaF2 – fluorite/Na2O- antifluorite
diamond
ZnS- blende
B. Structures derived from hexagonal close packed
1. NiAs – nickel arsenide
2. ZnS – wurtzite
3. CdI2 – cadmium iodide
C. Non close packed structures
1. CsCl – cesium chloride
2. MoS2 - molybdenite
D. Metal oxide structures
1. TiO2- rutile
2. ReO3 – rhenium trioxide
3. CaTiO3 – perovskite
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MgAlO4 - Spinel
49
C1: CsCl- Cesium Chloride (Pm-3m)
½
•Cl- ions form a primitive array  Cubic lattice
•C.N.: Cs - 8 (cubic) : Cl - 8 (cubic)
• One Cl atom at (0,0,0);
•One Cs at (1/2,1/2,1/2)
•1CsCl unit in the cell
Adopted by chlorides, bromides and iodides of large cations: Cs+, Tl+, NH4+
Adopted by intermetallic compounds: CuZn, CuPd, TiX with X=Fe, Co, Ni;
etc.
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C2: MoS2 – Molybdenite (P63/mmc)
¼ , 5/8, 7/8
1/
8,
3/
8,
Layers of edge shared MoS6 trigonal prisms
¾
Hexagonal layers of S are not close-packed in 3D Hexagonal lattice
•2Mo at (2/3,1/3,3/4) and (1/3,2/3,1/4)
• 4I 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
•C.N.: Mo - 6 (Trigonal Prismatic) : S 3 (base pyramid)
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MoS2
vs.
CdI2
B
A
A
A
B
B
B
A
A
B
A
A
MoS2
CdI2
Staggered stacks of prisms
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Eclipsed stacks of octahedra
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Compounds with MoS2 structure
Compounds of type: TX2
where T = transition metal of group IVB, VB or VIB
X= S, Se, Te
Anisotropic electronic properties due to the layered structure
Ion intercalation gives mixed valence materials with interesting physics
MoS2, ZrS2, and HfS2 when intercalated with alkali metals become superconducting
Li-intercalation in MoS2 changes the coordination of Mo from trigonal prismatic to Oh
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A. Structures derived from cubic close packed
1.
2.
3.
4.
NaCl- rock salt
CaF2 – fluorite/Na2O- antifluorite
diamond
ZnS- blende
B. Structures derived from hexagonal close packed
1. NiAs – nickel arsenide
2. ZnS – wurtzite
3. CdI2 – cadmium iodide
C. Non close packed structures
1. CsCl – cesium chloride
2. MoS2 - molybdenite
D. Metal oxide structures
1. TiO2- rutile
2. ReO3 – rhenium trioxide
3. CaTiO3 – perovskite
4.5/23/2013
MgAlO4 - Spinel
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D1: Rutile, TiO2(P42/mnm)
Chains of edge
shared TiO6 Oh on
c direction
Edge-shared
chains are
linked by
corners
Blue spheres Ti4+
Red spheres O2-
•O2- ions form a distorted h.c.p. array or a
tetragonal structure
Two unit cells on top of each
other are shown
C.N.: Ti - 6 (Oh) : O - 3 (trigonal planar)
•Ti4+ fills ½ of the Oh voids
½
• two Ti4+ ions at (0, 0, 0) and (1/2, 1 / 2, 1 /2)
• four O2- at ±(0.3, 0.3, 0) and (0.8, 0.2, 1 /2)
0, 1
0,1
½
0,1
½
• 2TiO2 per unit cell (Ti2O4)
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TiO2 (Rutil): tetragonal structure resulted from h.c.p.
distortion
TiO2 – is a 3 D structure!!!
Strong M-O bonds
distortion
h.c.p.
tetragonal
network of corner sharing Oh in a h.c.p.
array made of O2- ions with Ti4+ filling ½ of
Oh sites in an alternant manner: one full
then one empty
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CdI2
vs.
TiO2
h.c.p. array of I- with Cd2+ in ½ Oh voids
h.c.p. array of O2- with Ti4+ in ½ Oh voids
The Oh voids in one layered empty
The Oh voids are alternating in a layer
 Layered structure
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
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3D structure
57
Examples of TiO2 –type structure adoption
Oxides: MO2 (e.g. Ti, Nb, Cr, Mo, Ge, Pb, Sn)
Fluorides: MF2 (e.g. Mn, Fe, Co, Ni, Cu, Zn, Pd)
Rutile-type oxides with one or more d electrons often display remarkable
electronic and magnetic properties.
TiO2
Ti4+ (d0)are equidistant
MoO2
Mo4+ (d2)
One type of M-M bonds (2.96Å)
(in Ti metal, Ti-Ti bond is 2.92Å)
Alternating short (2.51Å vs 2.725Å in Mo metal)
and long M-M bonds
TiO2-x  anisotropic conductor (extensive overlap of the d-orbitals along c axis and no
orbital overlap on the perpendicular direction  the conductivity in the ab plane is  3 order
of magnitude smaller than on the c axis)
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Structure -properties relationship in the rutile compounds
TiO2-rutile
Ti,
d0 ion
-insulator
VO2-rutile type
V, d1 ion -metal
VO2-monoclinic
V, d1 ion in a distorted
structure-insulator
2 Ti t2g orbitals overlap with O p orbitals  metal-oxygen π band
1 Ti t2g orbital (along the tetragonal c axis) forms nonbonding cation sublattice
band (the conduction band,  )
(a) empty
(b) partially filled by the 2 e- of V
(c) split into localized bonding and antibonding levels
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TiO2 polymorphs
Anatase
750 C

915 C

Tetragonal
*Eg=2.04eV
Brookite
Rutile
Tetragonal
*Eg = 1.78eV
Orthorhombic
*Eg = 2.20eV
* Calculated values
 High refractive index; Excellent optical transmittance in the VIS and NIR region; High
dielectric constant;
All have been studied for their photocatalytic and photoelectrochemical applications.
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D2: Rhenium Trioxide, ReO3 (bronzes)(Pm-3m)
Black spheres Re6+
Red spheres O2-
Corner shared ReO6 Oh
•Defective f.c.c. array : one oxygen site on the face
C.N.: Re - 6 (Oh) : O - 2 (linear)
missing; Cubic lattice
0, ½ , 0
0,1
• Re at (0, 0, 0);
0,1
•3O at (1/2, 0, 0), (0, 1/2, 0), (0, 0, 1/2)
•1ReO3 per unit cell
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Compounds with ReO3 structure
Oxides: WO3 , UO3,
Fluorides: AlF3, ScF3 , FeF3 , CoF3, MoF3
Others: Sc(OH)3, TaO2F, Cu3N,
ternary structures derived
from this 3D octahedral
network are among the most
important in oxide
chemistry
Re6+ is d1 system and metallic conductivity is expected
Ion intercalation/substitution led to mixed oxidation state magnetic and electronic
properties
Ex: WO3 is a band insulator with a band gap of 2.6 eV
WO3-xFx – superconducts at 0.4K (x up to 0.45
Li doped WO3 is metallic
Na doped WO3 shows superconductivity (NaxWO3 (0.2 < x < 0.4), 0.7 K < Tc < 3 K
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