the structures of simple solids - yazd chemistry... · 2016-01-04 · 1 [email protected]. 1 the...
TRANSCRIPT
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The structures of
simple solids
Alireza Gorji
Department of Chemistry, Yazd University
Solid State Chemistry
• Introduction
• Metals
• Alloys
• Ionic Solids
• Crystal Defects
• Band Theory
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The 14 possible BRAVAIS LATTICES {note that spheres in this picture represent lattice points, not atoms!}
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6
1926 Goldschmidt proposed atoms could be
considered as packing in solids as hard spheres
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Hexagonal
Close-Packing
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Features of Close-Packing
Coordination Number = 12
74% of space is occupied
Largest interstitial sites are: octahedral (O) ( r = 0.414) ~ 1 per sphere
tetrahedral (T±) (r = 0.225) ~ 2 per sphere
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A NON-CLOSE-PACKED structure adopted by some metals is:
68% of space is occupiedCoordination Number 8
8 Nearest Neighbors at 0.87a
6 Next-Nearest Neighbors at 1a
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bcc
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Some of these intermetallic compounds contain a very electropositive metal
(for example, K or Ba) in combination with a less electropositive metal or
metalloid (for example, Ge or Zn), and in a Ketelaar triangle lie above the true
alloys. Such combinations are called Zintl phases.
Molecular
Solids
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CCP Cl- with Na+ in all Octahedral holes
Lattice: fcc
4NaCl in unit cell
Coordination: 6:6 (octahedral)
Cation and anion sites are topologically identical
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CaF2 Fluorite / {Na2O Anti-Fluorite}
CCP Ca2+ with F- in all Tetrahedral holes
Lattice: fcc
4CaF2 in unit cell
Coordination: Ca2+ 8 (cubic) : F- 4 (tetrahedral)
In the related Anti-Fluorite structure Cation and Anion positions are reversed
CaF2 Fluorite / {Na2O Anti-Fluorite}
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ZnS Zinc Blende (Sphalerite)
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ZnS Zinc Blende (Sphalerite)
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CCP S2- with Zn2+ in half Tetrahedral holes (only
T+ {or T-} filled)
Lattice: fcc
4ZnS in unit cell
Coordination: 4:4 (tetrahedral)
Cation and anion sites are topologically identical
ZnS Zinc Blende (Sphalerite)
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NaCl (Halite)
Very common (inc. 'ionics', 'covalents' & 'intermetallics' )
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)
Examples of Structure Adoption
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COMPLEX-ION VARIANTS
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NiAs Nickel Arsenide
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HCP As with Ni in all Octahedral holes
Lattice: Hexagonal - P
a = b, c (8/3)a
2NiAs in unit cell
Coordination: Ni 6 (octahedral): As 6
(trigonal prismatic)
NiAs Nickel Arsenide
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ZnS WurtziteHCP S2- with Zn2+ in half Tetrahedral holes
(only T+ {or T-} filled)
Lattice: Hexagonal - P
a = b, c (8/3)a
2ZnS in unit cell
Coordination: 4:4 (tetrahedral)
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Comparison of Wurtzite and Zinc Blende
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Comparison of Wurtzite and Zinc Blende
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NON CLOSE-PACKED STRUCTURES
CsCl Cesium Chloride
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CsCl Cesium Chloride
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Lattice: Cubic - P (N.B. Primitive!)
1CsCl in unit cell
Coordination: 8:8 (cubic)
Adoption by chlorides, bromides and iodides of
larger cations, e.g. Cs+, Tl+, NH4+
CsCl Cesium Chloride
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The Spinel structure AB2O4
Normal Spinel
O2- fcc
AII (1/8)hT
BIII (1/2)hO
MgAl2O4
The rationalization of structures
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The energetics of ionic bonding
Lattice enthalpy and the Born–Haber cycle
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The electronic structures of solids
The conductivities of inorganic solids
Band formation by orbital overlap
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Extrinsic semiconductors
Intrinsic
semiconductors
Ge/As Ge/Ga