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SCES2338: SOLID STATE CHEMISTRY
A. Outline of the Overall Topic
Course Content1 Crystal and close-packed structures
2 Bonding in solids specifically ionic and partial covalent bonding
3 Bonding in metals and band theory
4 Crystal imperfections
5 Cases of non-stoichiometry in compounds and solid solutions
6 Phase diagrams
7 Electrical, magnetic and optical properties
References
1 West, A. R. (1996). Basic Solid State Chemistry. John Wiley & Sons.
2 Rodgers, G. E. (1994). Introduction to Coordination Solid State and Descriptive
Chemistry.
3 Christman, J. R. Fundamentals of Solid State Physics.
4 Ladd, M. F. F. (1979). Structure and Bonding in Solid State Chemistry. Halsted Press.
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SCES2338: SOLID STATE CHEMISTRY
A. Outline of the Overall Topic
Timetable
Tuesday: 9.00-9.50 AM D112; Dr. Rusnah Syahila; L6-29
Thursday: 9.00-9.50 AM D112; Dr. Nor Asrina ; L7-33
Examination Schedule
4-January-2013
11.30 AM
B. Assessment Method
Evaluation
1 Final examination: 70%
2 Continuous assessment: 30%
Soft Skills
1 CRITICAL THINKING AND PROBLEM SOLVING SKILLS
CT2 (The ability to develop and improve thinking skills such as to explain, analyse and evaluate discussions)
2
COMMUNICATION SKILLS
CS1 (The ability to present ideas clearly, effectively and confidently, in both oral and written forms)
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SCES2338: SOLID STATE CHEMISTRY
1.0 Introduction to Solid State Chemistry
Historical PerspectiveMaterials are so important in the development of civilization
Stone Age natural materials (stone, clay, skins, and wood).
Bronze Age (3000 BC) people found copper and how to make it harder by alloying
1200 BC use of iron and steel, a stronger material that gave advantage in wars
1850 discovery of a cheap process to make steel, which enabled the railroads and
the building of the modern infrastructure of the industrial world.
http://www.llbchamber.ca
monaghan.ie
http://www.exploringsurreyspast.org.uk
https://mywebspace.wisc.edu http://www.ehow.com
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SCES2338: SOLID STATE CHEMISTRY
1.0 Introduction to Solid State Chemistry
Material Science and EngineeringUnderstanding of how materials behave and why they differ in properties
Materials Science: the combination of physics, chemistry, and the focus on the
relationship between the properties of a material and its microstructure.
Materials Engineering: the development of material science allowed designing
materials and provided a knowledge base for the engineering applications.
Structure: At the atomic level: arrangement of atoms in different ways. (Gives different
properties for graphite than diamond both forms of carbon.)
Properties are the way the material responds to the environment. For instance, the
mechanical, electrical and magnetic properties are the responses to mechanical,
electrical and magnetic forces, respectively. Other important properties are thermal(transmission of heat, heat capacity), optical(absorption, transmission and scattering of
light), and the chemical stabilityin contact with the environment (like corrosion
resistance).
Processing of materials is the application of heat (heat treatment), mechanical forces,
etc. to affect their microstructure and, therefore, their properties.
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SCES2338: SOLID STATE CHEMISTRY
1.0 Introduction to Solid State Chemistry
Why Study Material Science and Engineering
To be able to select a material for a given use based on considerations of cost and
performance.
To understand the limits of materials and the change of their properties with use.
To be able to create a new material that will have some desirable properties.
All engineering disciplines need to know about materials. Even the most "immaterial",
like software or system engineering depend on the development of new materials,
which in turn alter the economics, like software-hardware trade-offs. Increasing
applications of system engineering are in materials manufacturing (industrial
engineering) and complex environmental systems.
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SCES2338: SOLID STATE CHEMISTRY
1.0 Introduction to Solid State Chemistry
Classification of Materials
According to the way the atoms are bound together
Metals: valence electrons are detached from atoms, and spread in an 'electron
sea' that "glues" the ions together. Strong, conduct electricity and heat and are
opaque to light. Examples: aluminum, steel, brass, gold.Semiconductors: covalent bonding. Electrical properties depend on proportions
of contaminants. They are opaque to visible light but transparent to the
infrared. Examples: Si, Ge, GaAs.
Ceramics: atoms behave mostly like either positive or negative ions, and are
bound by Coulomb forces between them. Usually combinations of metals or
semiconductors with oxygen, nitrogen or carbon (oxides, nitrides, and carbides).
Examples: glass, porcelain, many minerals.
Polymers: bound by covalent forces and weak van der Waals forces, and usually
based on H, C and other non-metallic elements. They decompose at moderate
temperatures (100 400 C), and are lightweight. Other properties vary greatly.
Examples: plastics (nylon, Teflon, polyester) and rubber.
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SCES2338: SOLID STATE CHEMISTRY
1.0 Introduction to Solid State Chemistry
Solid materials are classified according to the regularity withwhich atoms or ions are arranged with respect to one another.
Crystalline Solids vs. Amorphous Solids
In crystalline materials atoms are
situated in a repeating array over
large atomic distances.
In amorphous materials long range
order do not exist
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SCES2338: SOLID STATE CHEMISTRY
1.0 Crystal Imperfections
Imperfections in solidsThe properties of some materials are greatly influenced by the presence
ofimperfections.
It is important to have knowledge about the types of imperfections that
exist and the roles they play in affecting the behavior of materials.
Atom Purity and Crystal PerfectionIf we assume a perfect crystal structure containing pure elements, then
anything that deviated from this concept or intruded in this uniform
homogeneity would be an imperfection.
1. Real crystalline solids are almost never perfect.
2. Many materials are technologically of value because they are disordered.
3. Many material properties are improved by the presence of imperfections
and deliberately modified (alloying and doping).
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SCES2338: SOLID STATE CHEMISTRY
1.0 Solidification
Solidification
result of casting of molten material
2 steps
- Nuclei form
- Nuclei grow to form crystals grain structure
Start with a molten material all liquid
grain structurecrystals growingnuclei liquid
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SCES2338: SOLID STATE CHEMISTRY
1.0 Grain Boundaries
Regions between crystals
Transition from lattice of
one to that of the other
Slightly disordered
Low density in grainboundaries
- high mobility
- high diffusivity
-high chemical reactivity
grain can be
- roughly same size in all
directions
- columnar
Adapted from Fig. 5.12,
Callister & Rethwisch 3e.
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SCES2338: SOLID STATE CHEMISTRY
1.0 Structural Imperfections (Defects) in Crystalline Solids
Perfect crystal vs. Imperfect crystal
all atoms on their correct lattice positions
(actual positions affected by extent of
thermal vibrations which can be
anisotropic)
1. Point defects (0-Dimension)
2. Line defects (1-D)
3. Interfacial defects (2-D)
4. Volume defects (3-D)
Imperfections can be classified according to their dimensionality
Intrinsic defects - do not change overall composition- stoichiometric defects
- two common types: Schottky and Frenkel defects
Extrinsic defects - created when foreign atom(s) introduced or there isvalence change
Real crystals contain both intrinsic and extrinsic defects
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SCES2338: SOLID STATE CHEMISTRY
1.0 Types of Imperfections (Defects)
Crystal defects
Point defects Line defects Volume defects
Self interstitial
Interfacial defects
Inclusions
VoidsScrew dislocations
Edge dislocations
Schottky
Vacancy
Frenkel
Substitutional
Colour centres
Grain boundaries
Tilt boundaries
Twin boundaries
Stacking faults
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SCES2338: SOLID STATE CHEMISTRY
1.0 Point Defects in Crystals
0D(Point defects)
Vacancy
Impurity
Frenkel defect
Schottky defect
Non-ionic
crystals
Ioniccrystals
Interstitial
Substitutional
Other
Zero Dimensional or Point Defects
Vacancy equals an empty lattice site.
Interstitialcy equals an atom occupying a site between atoms inthe crystal lattice.
Schottky defect - cation - anion vacancy pair in an ionic crystal.
Frenkel defect - vacancy interstitial pair in an ionic lattice.
Point defects provide opportunity for atomic mixing.
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SCES2338: SOLID STATE CHEMISTRY
1.0 Point Defects in Crystals: Vacancy
Missing atom from an atomic siteAtoms around the vacancy displaced
Stress field produced in the vicinity of the vacancy
Based on their origin vacancies can be
Random/Statistical (thermal vacancies, which are required by
thermodynamic equilibrium) or Structural (due to off-stoichiometry in a compound)
Based on their position vacancies can be random or ordered
Vacancies play an important role in diffusion of substitutional atoms
Non-equilibrium concentration of vacancies can be generated by:
quenching from a higher temperature or
by bombardment with high energy particles
Vacancy
distortion
of planes
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SCES2338: SOLID STATE CHEMISTRY
1.0 Point Defects in Crystals: Impurity
Impurity
Interstitial
Substitutional
Tensile Stress
Fields
Or alloying element
Foreign atom replacing
the parent atom in the
crystal
Compressive
stress fields
-Interstitials exist for
cations.
-interstitials are not
normally observed for
anions because
anions are large
relative to the
interstitial sites
Cation
interstitial
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SCES2338: SOLID STATE CHEMISTRY
1.0 Impurities in Metals
OR
Substitutional solid soln.
(e.g., Cu in Ni)
Interstitial solid soln.
(e.g., C in Fe)
Second phase particle
-- different composition
-- often different structure.
Two outcomes if impurity (B) added to host (A): Solid solution ofB in A (i.e., random dist. of point defects)
Solid solution ofB in A plus particles of a new
phase (usually for a larger amount of B)
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SCES2338: SOLID STATE CHEMISTRY
1.0 Impurities in Ceramics
Electroneutrality (charge balance) must be maintainedwhen impurities are present
Eg: NaCl Na+ Cl-
Substitutional cation impurity
without impurity Ca2+ impurity with impurity
Ca2+
Na+
Na+Ca2+
cation
vacancy
Substitutional anion impurity
without impurity O2-impurity
O2-
Cl-
an ion vacancy
Cl-
with impurity
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SCES2338: SOLID STATE CHEMISTRY
1.0 Impurities in Polymers
Defects due in part to chain packing errors and impurities such as
chain ends and side chains
Callister & Rethwisch 3e.
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SCES2338: SOLID STATE CHEMISTRY
1.0 How Do Impurities Affect the Structure and Properties of A Solid?
To obtain a perfectly pure substance is almost impossible.Purification is a costly process.
In general, analytical reagent-grade chemicals are of high purity, and yet
few of them are better than 99.9% pure.
This means that a foreign atom or molecule is present for every 1000
host atoms or molecules in the crystal. The most demanding of purity is
in the electronic industry.
Silicon crystals of 99.999 (called 5 nines) or better are required for IC
chips productions. These crystal are doped with nitrogen group elements
of P and As or boron group elements B, Al etc to form n- and p-typesemiconductors.
In these crystals, the impurity atom substitute atoms of the host crystals.
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SCES2338: SOLID STATE CHEMISTRY
1.0 How Do Impurities Affect the Structure and Properties of A Solid?
Presence of foreign atoms with one electron more or less than the
valence four silicon and germanium host atoms is the key of making n- a
and p-type semiconductors.
Having many semiconductors connected in a single chip makes the
integrated circuit a very efficient information processor.
The electronic properties change dramatically due to these impurities.
In other bulk materials, the presence of impurity usually leads to a
lowering of melting point.
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SCES2338: SOLID STATE CHEMISTRY
1.0 How Do Impurities Affect the Structure and Properties of A Solid?
For example, Hall and Heroult tried to electorlyze natural aluminum
compounds.
They discovered that using a 5% mixture of Al2O3 (melting point 273 K) in
cryolite Na3AlF6 (melting point 1273 K) reduced the melting point to 1223
K, and that enabled the production of aluminum in bulk.
Recent modifications lowered melting temperatures below 933 K.
Some types of glass are made by mixing silica (SiO2), alumina (Al2O3),
calcium oxide (CaO), and sodium oxide (Na2O).
They are softer, but due to lower melting points, they are cheaper to
produce.
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SCES2338: SOLID STATE CHEMISTRY
1.0 Point Defects in Crystals: Frenkel defects
In ionic crystal, during the formation of the defect the overall electrical neutrality hasto be maintained (or to be more precise the cost of not maintaining electrical
neutrality is high)
Frenkel defects
A cation vacancyCation being smaller get displaced to interstitial voids
A Frenkel defect usually occurs only on one sublattice of a crystal, and consists of
an atom or ion moving into an interstitial position thereby creating a vacancy.
For an alkali-halide-type structure, such as NaCl, where one cation moves out of
the lattice and into an interstitial site.
This type of behaviour is seen, for instance, in AgCl, where we observe such acation Frenkel defectwhen Ag+ ions move from their octahedral coordination
sites into tetrahedral coordination.
This kind of self interstitial costs high energy in simple metals and is not usually
found [Hf(vacancy) ~1eV; Hf(interstitial) ~3eV]
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SCES2338: SOLID STATE CHEMISTRY
1.0 Point Defects in Crystals: Schottky defects
Schottky defectsPair of anion and cation vacanciesFor a 1:1 solid MX, a Schottky defect consists ofa pairof vacant sites, a cation
vacancy, and an anion vacancy.
The number of cation vacancies and anion vacancies have to be equal to
preserve electrical neutrality.
A Schottky defect for an MX2 type structure will consist of the vacancy caused by
the M2+ ion together with two X anion vacancies, thereby balancing the
electrical charges.
Schottky defects are more common in 1:1 stoichiometry and examples of
crystals that contain them include rock salt (NaCl), wurtzite (ZnS), and CsCl.
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SCES2338: SOLID STATE CHEMISTRY
1.0 Point Defects in Crystals: Other defects
Other defects due to charge balanceIf Cd2+ replaces Na+ one cation vacancy is created
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SCES2338: SOLID STATE CHEMISTRY
1.0 Point Defects in Crystals: Methods of Producing Point Defects
Growth and synthesis- Impurities may be added to the material during synthesis
Thermal & thermochemical treatments and other stimuli- Heating to high temperature and quench
- Heating in reactive atmosphere- Heating in vacuum e.g. in oxides it may lead to loss of oxygen
Plastic Deformation
Ion implantation and irradiation- Electron irradiation (typically >1MeV)
Direct momentum transfer or during relaxation of electronic excitations)
- Ion beam implantation (As, B etc.)
- Neutron irradiation
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SCES2338: SOLID STATE CHEMISTRY
1.0 Thermodynamics of Point Defects
All macroscopic samples of materials contain some defects as defectformation is entropically favored ( the presence of vacancies increases the
entropy (randomness))
when defect formation is enthalpically very unfavorable there may be very
small numbers of defects
Free energy,
G = H - TS
Ener
gy
[defect]
Entropy, -TS
Enthalpy, H
at this point a breakdown in structure
will occur to form a new phase
requires energy to create defects !
H inc but S also inc
G = H - TS
Temperature
-TS incs with inc T moredefects at higher T
SC S2338 SO S C S
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SCES2338: SOLID STATE CHEMISTRY
1.0 How often Do Vacancies Jump
The equilibrium number of vacancies for a given quantity of material dependson and increases with temperature (an Arrhenius model).
Distance
Energy
Atom Vacancy
EV
Rj= Ro exp(-Ev/kBT)E
v= activation energy (energy needed by the atom to jump)
Rj= frequency of jumps (depend on temperature)
Ro= attempt frequency
kB=Boltzmann constant (1.381 x 10-23 J/K
T=temperature
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SCES2338: SOLID STATE CHEMISTRY
1.0 Thermodynamics of Point Defects
To follow dotted arrow - Na+ would have to push two Cl- apart to pass through to vacancy
Less energy needed to follow solid arrow
This is a close-packed
lattice, so the Cl-
ions are incontactNa+
Cl-
V-Na
migrating Na+
EV
length of jump
SCES2338 SOLID STATE CHEMISTRY
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SCES2338: SOLID STATE CHEMISTRY
1.0 How Many Vacancies are There?
NvN
=exp -EvkBT
Each lattice
site is a
potential
vacancy site
Equilibrium concentration varies with temperature!
Nv= number of defects
N= number of potential defect sitesEv= activation energy
kB=Boltzmann constant (1.381 x 10-23 J/K or 8.62 x 10-5 eV/K)
T=temperature
Ev obtained from an experiment.
Nv
N
T
exponentialdependence!
1/T
N
Nvln
-Ev/k
slope
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SCES2338: SOLID STATE CHEMISTRY
1.0 Line (Dislocation) Defects
Are one-dimensional defects around which atoms are misaligned Edge dislocation:
- extra half-plane of atoms inserted in a crystal structure
- b perpendicular () to dislocation line Screw dislocation:
- spiral planar ramp resulting from shear deformation
- b parallel () to dislocation line
Burgers vector, b: is a measure of lattice distortion and is measured as a distance
along the close packed directions in the lattice
EDGE
DISLOCATIONS
MIXED SCREW
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SCES2338: SOLID STATE CHEMISTRY
1.0 Line (Dislocation) Defects
Mixed dislocation. This dislocation
has both edge and screw character
with a single Burgers vector
consistent with the pure edge and
pure screw regions.
Screw dislocation. The spiral
stacking of crystal planes leads to
the Burgers vector being parallel to
the dislocation line.
Definition of the Burgers vector, b, relative to an edge dislocation. (a) In the
perfect crystal, an m n atomic step loop closes at the starting point. (b) In
the region of a dislocation, the same loop does not close, and the closure
vector (b) represents the magnitude of the structural defect. For the edge
dislocation, the Burgers vector is perpendicular to the dislocation line.
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SCES2338: SOLID STATE CHEMISTRY
1.0 Line (Dislocations) Defects
Dislocation is a boundary between the slipped and the unslipped partsof the crystal lying over a slip plane
slip between crystal planes result when dislocations move,
produce permanent (plastic) deformation.
Slipped
part
of the
crystal
Unslipped
part
of the
crystal
Deformation of Zinc:
before after tensile elongation
slip steps
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SCES2338: SOLID STATE CHEMISTRY
1.0 Imperfections in Solids
Edge Dislocation
Adapted from Fig. 5.9, Callister & Rethwisch 3e.
Screw Dislocation
Edge
Screw
MixedFig. 5.8, Callister & Rethwisch 3e.
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Plane/planar/surface/interfacial defects twin boundary (plane)
Essentially a reflection of atom positions across the twinplane.
Stacking faults
For FCC metals an error in ABCABC packing sequence
Ex: ABCABABC34
SCES2338: SOLID STATE CHEMISTRY
1.0 Interfacial Defects Twin & Stacking Faults Defects
Adapted from Fig. 5.14,
Callister & Rethwisch 3e.
change in crystalorientation during
growth
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SCES2338: SOLID STATE CHEMISTRY
1.0 Interfacial Defects Grain Defects
Solids generally consist of a number ofcrystallites or grains.
Grains can range in size from nanometers
to millimeters across and their orientations
are usually rotated with respect to
neighboring grains
Grain boundaries limit the lengths andmotions of dislocations
Therefore, having smaller grains (more
grain boundary surface area) strengthens a
material
The size of the grains can be controlled by
the cooling rate when the material cast orheat treated
Generally, rapid cooling produces smaller
grains whereas slow cooling result in larger
grains
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SCES2338: SOLID STATE CHEMISTRY
1.0 Volume (Bulk) Defects
Volume/bulk/area defectsBulk defects occur on a much bigger scale than the rest of the crystal defects
VoidsVoids are regions where there are a large number of atoms missing from the lattice.
When voids occur due to air bubbles becoming trapped when material solidifies, it is
commonly called porosity. When a void occurs due to the shrinkage of a material as itsolidifies, it is called cavitation.
InclusionsImpurity atoms cluster together to form small regions of a different phase. The term
phase refers to that region of space occupied by a physically homogeneous material.
These regions are often called precipitates or inclusions.
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SCES2338: SOLID STATE CHEMISTRY
1.0 Visualization of Defects
Crystallites (grains) and grain boundaries. Vary considerably in size. Canbe quite large.
Crystallites (grains) can be quite small (mm or less) necessary to
observe with a microscope (OPM, SEM, STM).
Scanning Tunneling Microscopy (STM)Optical Polarizing Microscopy (OPM)
Carbon
monoxide
molecules
arranged on a
platinum (111)
surface.
Iron atoms
arranged on a
copper (111)
surface.
Photos produced from the work of C.P. Lutz, Zeppenfeld, and D.M.
Eigler.
0.75mm
Micrograph of
brass (a Cu-Zn alloy)
Adapted from Fig. 5.18(b) and (c), Callister & Rethwisch 3e. (Fig. 5.18(c) is
courtesy of J.E. Burke, General Electric Co.)
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SCES2338: SOLID STATE CHEMISTRY
1.0 Importance of Imperfections
Most of the properties of materials are affected by imperfections:
Small amount of impurity atoms may increase the electrical conductivity
of semi conductors.
Dislocations are responsible for ductility.
Strength of materials can be increased to a large extent by the
mechanism strain-hardening which produces line defects that act as a
barrier to control the growth of other imperfections.
Presence of bulk defects such as cracks, notches, holes causes brittle
materials, which break at very low stresses without showing large
deformations.