This document discusses different types of solids and their structures. It describes two main types of solids - crystalline and amorphous. Crystalline solids have long-range order while amorphous solids have short-range order. Crystalline solids are further divided into molecular, ionic, covalent and metallic solids based on the type of bonding between particles. The document also discusses crystal structures, unit cells, Bravais lattices and close packing of spheres. It covers defects in solids and electrical, magnetic and optical properties of materials.

1. THE SOLID STATE
Dr. K.S. VIKAS 1

2. CONTENTS
 Types of solids
 Types of structures adopted by solids
Imperfections in solids
Dr. K.S. VIKAS 2

3. SOLIDS can be divided into two categories.
 Crystalline
 Amorphous
Crystalline has long range order
Amorphous materials have short range order
Dr. K.S. VIKAS 3

4. Dr. K.S. VIKAS
• Crystalline solid: well-ordered, definite arrangements of
molecules, atoms or ions.
• Crystals have an ordered, repeated structure.
• sharp melting point
• Anisotropy
• True solids
• Amorphous solid: no definite arrangement of molecules,
atoms, or ions (i.e., lack well-defined structures or
shapes).
• Amorphous solids vary in their melting points.
• Isotropy
• Pseudo solids (super cooled liquids)
Types of Solids
4

5. Dr. K.S. VIKAS 5

6. Molecular Solids Covalent Solids Ionic solids
Metallic solids
Na+
Cl-
STRUCTURE AND TYPES OF
CRYSTALLINE SOLIDS
Dr. K.S. VIKAS 6

7. Types of Crystalline Solids
1. Molecular Solids
• Lattice points occupied by molecules
• Held together by intermolecular forces like
London forces, dipole-dipole force or hydrogen
bonding
• Soft, low melting point
• Poor conductor of heat and electricity
Dr. K.S. VIKAS 7

8. Types of Crystalline Solids
2. Ionic Solids
• Lattice points occupied by cations and anions
• Held together by electrostatic attraction
• Hard, brittle, high melting point
• Poor conductor of heat and electricity
CsCl ZnS CaF2
Dr. K.S. VIKAS 8

9. Types of Crystalline Solids
3. Covalent Solids
• Lattice points occupied by atoms
• Held together by covalent bonds
• Hard, high melting point
• Poor conductor of heat and electricity
diamond graphite
carbon
atoms
Dr. K.S. VIKAS 9

10. Types of Crystalline Solids
4. Metallic Solids
• Lattice points occupied by positive metal ions
• Held together by metallic bonds
• Soft to hard, low to high melting point
• Good conductors of heat and electricity
Cross Section of a Metallic Crystal
nucleus &
inner shell e-
mobile “sea”
of e-
Dr. K.S. VIKAS 10

11. Crystal
Type
Particles Interparticle
Forces
Physical Behaviour Examples
Molecular
Ionic
Covalent
or Network
Metallic
Molecules
Positive
and
negative
ions
Atoms
Positive
metal ions
Dispersion
Dipole-
dipole
H-bonds
Electrostatic
attraction
Covalent
Metallic
bond
 Fairly soft
 Low to moderate mp
 Poor thermal and electrical
conductors
Hard and brittle
 High mp
 Good thermal and electrical
conductors in molten
condition
• Very hard
• Very high mp
• Poor thermal and electrical
conductors
 Soft to hard
 Low to very high mp
 Mellable and ductile
 Excellent thermal and
electrical conductors
O2, P4, H2O,
Sucrose
NaCl, CaF2,
MgO
SiO2(Quartz)
C (Diamond)
Na, Cu, Fe
TYPES OF CRYSTALLINE SOLIDS
Dr. K.S. VIKAS 11

12. CRYSTAL STRUCTURE
Cristal Lattice: Crystal Lattice is the arrangement of points in
three dimensional space, representing constituent particles in a
crystal.
Space Lattice  Arrangements of atoms
= Lattice of points onto which the atoms are hung.
Elemental solids (Argon): Basis = single atom.
Polyatomic Elements: Basis = two or four atoms.
Complex organic compounds: Basis = thousands of atoms.
+
Space Lattice + Basis = Crystal Structure
=
• • •
• • •
• • •
Dr. K.S. VIKAS 12

13. Definitions
1. The unit cell
“The smallest repeat unit of a crystal structure,
which when repeats in all the three dimensions to
form the crystal”
The unit cell is a box with:
• 3 sides - a, b, c
• 3 angles - , , 
Dr. K.S. VIKAS 13

14. Dr. K.S. VIKAS
Unit Cells
The smallest repeating unit that shows
the symmetry of the pattern is called the
unit cell.
Structures of Solids
14

15. TWO DIMENTIONAL UNIT CELL POSSIBILITIES OF NaCl
Na+
Cl-
Dr. K.S. VIKAS 15

16. Primitive ( P ) Body Centered ( I )
Face Centered ( F ) End-Centered (C )
LATTICE TYPES
Dr. K.S. VIKAS 16

17. Lattices
 In 1848, Auguste Bravais demonstrated
that in a 3-dimensional system there are
fourteen possible lattices
 A Bravais lattice is an infinite array of
discrete points with identical environment
 seven crystal systems + four lattice
centering types = 14 Bravais lattices
Auguste Bravais
(1811-1863)
Dr. K.S. VIKAS 17

18. BRAVAIS LATTICES
7 UNIT CELL TYPES + 4
LATTICE TYPES = 14
BRAVAIS LATTICES
Dr. K.S. VIKAS 18

19. Dr. K.S. VIKAS
• Three common types of Cubic unit cell.
• Primitive cubic, atoms at the corners of a simple cube
– each atom shared by 8 unit cells;
Common Types of Cubic Unit Cells
19
• Body-centered cubic (bcc), atoms at the corners of a
cube plus one in the center of the body of the cube,
– corner atoms shared by 8 unit cells, center atom completely
enclosed in one unit cell;
• Face-centered cubic (fcc), atoms at the corners of a
cube plus one atom in the center of each face of the cube,
– corner atoms shared by 8 unit cells, face atoms shared by 2
unit cells.

20. Dr. K.S. VIKAS 20

21. Shared by 8 unit cells
Shared by 2 unit cells
Dr. K.S. VIKAS 21

22. Dr. K.S. VIKAS
Unit Cells
22

23. Dr. K.S. VIKAS 23
Table showing Atom Fractions
in Unit Cells
Position in the
Unit Cell
Fraction in the
unit cell
Corner 1/8
Body Centre 1
Face Centre 1/2

24. 1 atom/unit cell
(8 x 1/8 = 1)
2 atoms/unit cell
(8 x 1/8 + 1 = 2)
4 atoms/unit cell
(8 x 1/8 + 6 x 1/2 = 4)
Number of Atoms in a Unit Cell
Dr. K.S. VIKAS 24

25. CLOSE-PACKING OF SPHERES
Dr. K.S. VIKAS 25

26. CLOSE-PACKING IN TWO DIMENSIONS
SQUARE PACKING
AAA…. Type
Each particle in contact with
4 others
HEXAGONALCLOSE PACKING
ABAB…. Type
Each particle in contact with
6 others
Dr. K.S. VIKAS 26

27. TWO LAYERS PACKING
Dr. K.S. VIKAS 27

28. THREE LAYERS PACKING
Dr. K.S. VIKAS 28

29. Dr. K.S. VIKAS 29

30. Hexagonal close packing Cubic close packing
Dr. K.S. VIKAS 30

31. Packing Efficiency
volume of sphere
Packing Efficiency =---------------------------- X 100
Total volume of cube
Dr. K.S. VIKAS 31
(N)x (4/3 Π r3)
= --------------------- X100
a3

32. Dr. K.S. VIKAS 32

33. Packing Efficiency of Primitive Cubic Crystal
volume of sphere
Packing Efficiency =---------------------------- X 100
Total volume of cube
Dr. K.S. VIKAS 33
(N)x (4/3 Π r3)
= --------------------- X100
a3
1 x (4/3 Π r3)
= --------------------- X100
(2r)3
= 52.4%

34. Packing Efficiency of Body Centred Cubic
Crystal
volume of sphere
Packing Efficiency =---------------------------- X 100
Total volume of cube
Dr. K.S. VIKAS 34
(N)x (4/3 Π r3)
= --------------------- X100
a3
2 x (4/3 Π r3)
= --------------------- X100
(4/3 r)3
= 68%

35. Packing Efficiency of bcc, hcp & ccp
volume of sphere
Packing Efficiency =---------------------------- X 100
Total volume of cube
Dr. K.S. VIKAS 35
(N)x (4/3 Π r3)
= --------------------- X100
a3
4 x (4/3 Π r3)
= --------------------- X100
(2√2 r)3
= 74%

36. NON-CLOSE-PACKED STRUCTURES
68% of space is occupied
Coordination number = 8
a) Body centered cubic ( BCC ) b) Primitive cubic ( P)
52% of space is occupied
Coordination number = 6
Dr. K.S. VIKAS 36

37. Dr. K.S. VIKAS
Face-Centered Cubic Crystal Structure
68% of space is occupied
Hexagonal close packing &
Cubic close packing also
occupy the same space

38. Dr. K.S. VIKAS 38

39. TETRAHEDRAL HOLES
OCTAHEDRAL HOLES
TYPE OF HOLES IN CLOSE PACKING
Dr. K.S. VIKAS 39

40. Imperfections in Solids
or
crystal defects

41. Crystal Defects
• Perfect crystals do not exist; even the best crystals have
defects.
– defects are imperfections in the regular repeating
pattern
– Point defect
– Line defect
1. Point Defects
A.Vacancies
– given a perfect crystal (e.g. of Cu), an atom can be placed
on the outside of the cell to produce a vacancy (≡ □).
Dr. K.S. VIKAS 41

42. Types of Defects
Stoichiometric Defects:
stoichiometry is not disturbed
Non-stoichiometric Defects:
stoichiometry is disturbed
Impurity defects

43. Stoichiometric Defects
Schottky defect
Frenkel defect
Non-stoichiometric Defects
Metal excess defect
Metal deficiency defect

44. 1. Stoichiometric Defects
1) Shottky Defect
– equal numbers
of anion and cation vacancies.
– may be randomly distributed, but tend
to cluster because of oppositely charged
vacancies.
– most important with alkali halides.
Dr. K.S. VIKAS 44

45. 2) Frenkel Defect
Dislocation of cation
 cation occupies
interstitial position (void
between normal atomic
position).
Dr. K.S. VIKAS 45

46. Non-stoichiometric Defects
Metal excess defect
anion vacancies
excess cation
Metal deficiency defect
cation vacancies

47. Metal excess
defect
Anion vacancies
An anion is missing from the
crystal lattice and that place
is occupied by an electron
Color Centers (F-center; Ger:
farbenzentre)
Dr. K.S. VIKAS 47

48. Excess cation: in interstitial places

49. Metal deficiency defect cation
vacancies

50. 3. Impurity defect

51. Electrical Properties

52. Conductors
Insulators
Semiconductors
52

53. Energy (Eg) required to promote electrons from the valence band to the
conduction band.
Energy Gap

54. Insulators
 In insulators there are no free
electrons to move throughout
the material.
 Inter-atomic bonding is ionic or
strongly covalent. The valence
electrons are tightly bonded,
highly localized and not free to
scatter throughout the crystal.
 The band-gap is large, the
valence band is full, and the
conduction band is empty.
54
• Insulators:
-- wide band gap (> 2 eV)
-- few electrons excited
across band gap
Energy
filled
band
filled
valence
band
filled
states
GAP
empty
band
conduction

55. 55
Semiconductors
• Semiconductors:
-- narrow band gap (< 2 eV)
-- more electrons excited
across band gap
Energy
filled
band
filled
valence
band
filled
states
GAP
?
empty
band
conduction
 In semiconductors,
bonding is
predominantly covalent
(relatively weak).
 These electrons are
more easily removed by
thermal excitation.
 The band-gap is
smaller, the valence
band is full, and the
conduction band is
empty.

56. 56
Conductors
-- for metals, empty energy states are adjacent to filled states.
• two types of band
structures for metals
• thermal energy
excites electrons
into empty higher
energy states.
- partially filled band
- empty band that
overlaps filled band
filled
band
Energy
partly
filled
band
empty
band
GAP
filled
states
Partially filled band
Energy
filled
band
filled
band
empty
band
filled
states
Overlapping bands

57. Semiconductors
Intrinsic semiconductors
Extrinsic Semiconductors

58. Intrinsic Semiconductor
materials
 Silicon and germanium each
have 4 electrons in their outer
orbital. This allows them to
form crystals.
 In a silicon lattice, all silicon
atoms covalently bond to 4
neighbors, leaving no free
electrons to conduct electric
current. This makes a silicon
crystal an insulator rather than
a conductor.
A chip, an LED and a
transistor are all made
from semiconductor
material.

59. Intrinsic Semiconductor
 On heating some of the covalent bonds
between silicon atoms are broken and as a
result they conduct electricity
 Semiconductors in the pure form is called
intrinsic semiconductors

60. Extrinsic semiconductors
 They contain some suitable impurities in their crystal
lattice. This process of adding impurities to the crystal
is called doping . They are classified into two based on
the impurity present in it.
 n-type semiconductor
 p-type semiconductor

61. Doping Silicon to Create n-Type
Silicon
 The "dopant” has 5 valence electrons;
silicon has 4.
 Substituting a phosphorus atom with
5 valence electrons for a silicon atom
in a silicon crystal leaves an extra,
unbonded electron that is relatively
free to move around the crystal.

62. Doping Silicon to Create p-Type
Silicon
 The "dopant” has 5 valence
electrons; silicon has 4.
 Substituting a boron atom
with 3 valence electrons for a
silicon atom in a silicon
crystal leaves a hole (a bond
missing an electron) that is
relatively free to move around
the crystal.

63. When a dopant atom with a valence of less than four is substituted
into the silicon structure, a hole is created in the structure and an
acceptor energy level is created just above the valence band. Little
energy is required to excite the holes into motion.

64. Magnetic Properties
Diamagnetism
Paramagnetism
Ferromagnetism
Antiferromagnetism
Ferrimagnetism

65. Diamagnetism
Diamagnetic materials tend
to repel flux lines weakly
All the electrons are paired
They lose their magnetism in
the absence of external
magnetic field.
Examples: water, protein, fat

66. Paramagnetism
 Paramagnetic substances are attracted weakly by a
magnetic field.
 They lose their magnetism in the absence of external
magnetic field.
 They have one or more unpaired electrons.
 E.g. O2, Cu2+, Fe3+, Cr3+

67. Ferromagnetism
 Materials that retain a
magnetization in zero field
 They are attracted strongly
by a magnetic field
 They have more unpaired
electrons.
 Examples: iron, cobalt

68. Antiferromagnetism
 They are expected to be
ferromagnetic but shows
zero magnetic moment.
 The magnetic moments are
oppositely arranged and
hence cancel each other.
 Many metal oxides are
antiferromagnetic

69. Ferrimagnetism
 They are expected to be
ferromagnetic but shows only
small magnetic moment.
 The magnetic moments are
oppositely arranged but all
magnetic moments are not
canceled.
 E.g. Fe2O3