1. The Ideal

2. Square packing:
Not most space efficient
Hexagonal packing:
Most space efficient

3. Unit Cells: the simplest repeating motif
Can be different shapes and sizes
The
Rhomb
Is the
Unit cell
Shape Of
Hexagonal
lattices

4. Packing: layers build up 3D solid

5. Packing: layers build up 3D solid

6. ABABABAB . . . . Stacked up towards you
Packing direction
ABABABAB Stacked up towards you

7. hcp A B Hexagonal Packing direction Closest Packing: A B A B …

9. ccp A C B Cubic Closest Packing direction Packing: A B C A B C …

10. A C B CCP viewed as packing layers
CCP viewed as extended fcc unit cell
View ccp/fcc copper

11. a more realistic view of how to build up structure
Packing layers
a more realistic view of how to build up structure
sometimes not at all related to unit cell
Unit Cells:
a conceptual way to build up structure
sometimes resemble macroscopic crystalline solid
assigned symmetry types, like P21/c or P4mm called space groups
used in X-ray crystallography

12. ccp
hcp
bcc

14. More on Metals
Cubic closest packing makes metals malleable: easily bendable Cu and Ag
Work- hardening: creation of defects, loss of ccp lattice
Work hardening, strain hardening, or cold work is the strengthening of a material by increasing the material's dislocation density. Wikipedia
Alloys
Sterling Silver = Ag (92.5%) + Cu (7.5%), a substitutional alloy
Brass = Cu + Zn, a new structure, an intermetallic alloy
Steel = Fe + C (~1%), carbide steel, an interstitial alloy
Chrome = steel + Cr = Fe + C(~1%) + Cr(10%)
Stainless steel = chrome steel, both interstitial and substitutional alloy
“18/10” stainless is 18% Cr and 10% Ni
Galvanized Steel = steel with Zn layer
Molybdenum steel = Fe + C(<1%) + Cr(14%) + Ni(<2%) + Mo(1 %),
“martensitic” steel: very strong and hard

15. creates useful materials
Defects:
creates useful materials

16. Defects in
metal
structure

17. Smaller atom like C in iron
Larger atom
like P
in iron
Effect of added
atoms and
grains on
metal structure.
Defects and grain boundaries “pin” structure.
All these inhibit sliding planes and harden the metal.
Second crystal
phases
precipitated

18. Now consider red and blue balls the larger metal atoms;
Where are the interstitial sites?
Small alloy atoms, e.g. C,
Other metal atoms,
e.g. Cr or W,
replace metal atoms
Small alloy atoms fit into
Td sites and Oh sites

19. The Ideal

20. Ionic Solids as “Ideal structures”
Build up Ionic Solids conceptually like this:
assume Anions are larger than Cations, r- > r+
pack the Anions into a lattice: ccp, hcp or bcc
add Cations to the interstitial spaces
r- + r+
Diagonal=
2r- + 2r+
2 x r-
2 x r-

21. Consider red and blue balls the larger anions of A B packed layers;
Where do the cations go?
larger
anions
Larger cations,
r+/r- > 0.41
Smaller cations,
r+/r- < 0.41

22. Td cation holes are smaller than Oh holes
2x as many Td holes as Oh holes

23. Wurzite = Hexagonal ZnS
hcp S2- dianions (A B A packed) with Zn2+ cations in 1/2 Td holes.
Build it! See it! (as Chem3D)

25. Sphalerite or Zinc Blende = Cubic ZnS
ccp S2- dianions (A B C packed) with Zn2+ cations in 1/2 Td holes.
Build it! See it! (as Chem3D movie)

27. Fluorite = Cubic CaF2
ccp Ca2+ cations (A B C packed) with F2- anions in all Td holes.
Build it! See it! (as Chem3D movie)

29. Halite = NaCl
ccp Cl anions (A B C packed) with Na cations in all Oh holes.
Build it! See it in 3D!

31. These are the prototype structures:
CsCl - simple cubic, cation and anion CN 8, a 1:1 ionic solid
NaCl (Halite) - ccp anions & Oh cations; a 1:1 ionic solid
CaF2 (Fluorite) - ccp cations & Td anions; a 1:2 ionic solid
Cubic ZnS (sphalerite) - ccp anions & 1/2 Td cations; a 1:1 ionic solid
Hexagonal ZnS (wurzite) - hcp anions & 1/2 Td cations; a 1:1 ionic solid

32. Prototype Lattices 1:1 Ionic Solids 2:1 Ionic Solids
NaCl (halite) packing type: ccp packing, all Oh sites filled
cubic ion sites: both anion and cation six coordinate, Oh
ZnS (sphalerite) packing type: ccp packing, half Td sites filled
cubic ion sites: both anion and cation four coordinate, Td
ZnS (wurzite) packing type: hcp packing, half Td sites filled
hexagonal ion sites: both anion and cation four coordinate, Td
CsCl packing type: bcc packing
cubic ion sites: both anion and cation eoght coordinate, Oh
2:1 Ionic Solids
CaF2 (fluorite) packing type: ccp packing, all Td sites filled
cubic ion sites: anion four coordinate, Td
and cation eight coordinate, Oh

33. Other Structures are Described Based on Prototypes
Example 1. Galena - PbS “has the NaCl lattice”.
Note crystal morphology
Example 2. pyrite - Fe(S2) “has the NaCl lattice”, where (S22-) occupies Cl- site
With more deviations:
Example 3. tenorite- CuO: pseudo cubic where (O2-) occupies ABC sites and
Cu2+ occupies 3/4 ‘squashed’ Td sites.
Example CdI2: Layered Structure: I- forms hcp (ABA) layers and
Cd2+ occupies all Oh sites between alternate hcp (A B) layers
Example MoS2 : Layered Structure: S22- forms (AA BB) layers and
Mo4+ occupies all D3h sites between AA layers
Note similarity to graphite.
Used as lubricant.

34. One Prototype Layered Structure: Cadmium Iodide A B Cd2+ I-
Layers of hcp w/ Cd2+ in Oh sites A B
Cd2+ I-

35. Molybdenite, MoS2 Mo

36. Solid Film Lubricants: A Practical Guide
Extreme conditions could include high and low shaft speeds, high and low temperatures, high pressures, concentrated atmospheric and process contaminants, and inaccessibility.
Mineral oil-based fluid lubricants (oil and grease materials) function properly where the designed surface areas and shaft speeds allow for the effective formation of an oil film, as long as the machine operating temperature envelope falls between -20°C and 100°C (-4°F to 212°F). The only absolute limits that apply for fluid lubricants, regardless of the base oil type, are conditions that cause a change in the state of the fluid that prohibits fluid film formation. Fortunately, that is not the end of the story.
Various materials that protect interacting surfaces after the fluid film is lost have been either discovered or created. These materials may be applied to a surface in the form of an additive to a fluid lubricant, or in a pure form, and may also be added or alloyed into the surface when the component is being manufactured. The more common types of materials include the following:
* Molybdenum disulfide (MoS2) – also known as moly
* Polytetrafluoroethylene (PTFE) – also known as Teflon®
* Graphite

37. Muscovite
NaAl2(OH)2Si3AlO10)

38. Muscovite: layered silicates

39. Defects

40. Types of Defects Schottky defect, a vacancy defect Cl-vacancy
Na+ vacancy

41. an interstitial defect (extra atom or ion)
Types of Defects
2. Frenkel defect,
an interstitial defect
(extra atom or ion)
Interstitial Ag+

42. Types of Defects 3. F- center, (F, farbe, Ger.) or a color center
Trapped electron
NaCl + hn  Na+ + Cl + e-

43. Fluorite,
calcium fluoride,
CaF2
ummm, not white????

44. Types of Defects 4. Atom interchange 5. Substitutional
Cu and Au swap positions in an alloy

45. Defects:
The Beauty of Imperfection

46. Corundum, Al2O3

47. Al2O3
Corundum
Al(3+): CN=6, Oh
O(2-): CN=4, Td

48. The funny thing about corundum is, when you have it in a clean single crystal, you get something much different.
Sapphire is Gem-quality corundum
with Ti(4+) & Fe(2+) replacing Al(3+) in octahedral sites

49. Ruby
Gem-quality corundum
with ~3% Cr(3+) replacing Al(3+)
in octahedral sites

50. Emerald is the mineral beryl with substitution defects of Cr(3+) or V(3+) replacing Al(3+).
Beryl has the chemical composition Be3Al2(SiO3)6 and is classified as a cyclosilicate. It is the principal ore for the element beryllium.

51. Tsavorite is a variety of the mineral garnet a calcium-aluminosilicate with the formula Ca3Al2Si3O12. Crystal form is cubic. Trace amounts of vanadium or chromium provide the green color.
It is often called the Rolls-Royce of greens at Cadillac prices. From a collectors perspective, tsavorite is 200 times more rare than emerald, it is cleaner, more brilliant and not oiled or treated in any way.

52. Peridot is the gem-quality form of the mineral Olivine
Peridot is the gem-quality form of the mineral Olivine. It has the chemical composition (Mg,Fe)2SiO4, with Mg in greater quantities than Fe. The depth of green depends on how much iron is contained in the crystal structure, and varies from yellow-green to olive to brownish green. Peridot is also often referred to as "poor man's emerald". Olivine is a very abundant mineral, but gem-quality peridot is rather rare.
Polarized micrograph

53. Fe (2+) in Td (SiO4) sites heat + Ti(3+)
Quartz - SiO2 -simplest silicate mineral, piezoelectric, chiral!
heat
+ Ti(3+)

54. creates useful materials
Defects:
creates useful materials

55. Replace:
-S with I
-Zn with Hg
(at vertices)
-Zn with Ag
(in middle)
Sphalerite lattice
Replace:
-S with I
-Zn with Hg
(at vertices)
-Zn with Cu
(in middle)

56. heat
heat