1Solid-State Chemistry:

Structure and Properties

of Solids

2Solid-State Chemistry

Laboratory sessions (Weds)

1. ICSD and structure visualisation

(1-2 lab sessions)

2. Making a conducting polymer (2

lab sessions)

3Recommended Books

Basic Solid State Chemistry, A.R. West.

Inorganic Materials Chemistry, Shriver, Atkins

DoITPoMS Teaching and Learning Packages,

University of Cambridge,

www.msm.cam.ac.uk/doitpoms/tlplib

4Structure and bonding in

materials

REVISION SECTION:

Types of solids

Some important structure types

Basic crystallography

Read relevant sections in Inorganic Chemistry 4th ed by Shriver & Atkins (NB CHAPTER 3!)

Read DoITPoMS Teaching and Learning Packages

X-ray Diffraction Techniques (revision)

Atomic Scale Structure of Materials (do questions)

5Types of solids

Classification according to

chemical binding

and structure

6Important structure types

ccp (fcc); hcp; bcc; pc (sc)

ZnS

NaCl

CaF2

CsCl

ReO3

TiO2

BaTiO3

Covalent solids (diamond, graphite)

Molecular solids

Metals (intermetallics,

alloys,

Zintl phase)

Ionic

Covalent

networks

Molecular

7Simple Cubic Unit cells / Lattices

Metallic

Bonding and

properties

SCHEMATIC REPRESENTATION OF METALLIC SOLIDS

8Simple Cubic Unit cells / Lattices

Metallic

e.g. Po e.g. Au

e.g. Fe

9SCHEMATIC REPRESENTATION OF IONIC

SOLIDS

Ionic

Ionic

Bonding and

properties

10

STRUCTURES DERIVED FROM CUBIC

CLOSE PACKING (CCP)

Ionic

11

NiAs Nickel Arsenide

STRUCTURES DERIVED FROM

HEXAGONAL CLOSE PACKING (HCP)

ZnS Wurtzite (High T Form)

Ionic/covalent

12

CsCl Cesium Chloride

Ionic

13

ReO3 and WO3 (cubic)

(see S&A)

Ionic oxides ReO3 and WO3

14

BaTiO3(cubic or tetragonal)

(CaTiO3, SrTiO3 and mixed oxides. See S&A)

Ionic oxides BaTiO3

15

Covalent network solids

16

Molecular solidsMolecules (with intramolecular covalent bonds) and

intermolecular Van der Waals or non-covalent interactions)

Molecular solids

17

Types of solids

Classification according to

crystallinity or defects

Crystalline, polycrystalline, amorphous

Amorphous

Only short range order; no periodicity.

Powder x-ray diffraction has broad peaks

Melting point over a large range.

E.g. glasses, polymers and supercooled liquids

Crystallinecharacterized by 3-dimensional periodicity

Powder x-ray diffraction has sharp peaks

Sharp melting points

Distinct morphology

Examples of crystalline solids

Gypsum (CaSO4.H2O). A glass cannot be cleaved along particular planes

Quartz (recall that SiO2 can also exist as a glass)

Polycrystalline materials: grain structure

Iron-carbon alloy

Galvanised steel

Defects and grain structures.

Domain boundaries

Eutectoid of iron-carbon steel alloy grain boundaries

Single crystal

Polycrystalline material with grain boundaries

Liquid crystals

Liquid crystals.

characterized by 1- or 2-

dimensional order

rod- or disc-like molecules

Polymers

Polymers

only short range order; no

periodicity.

melting point over a large

range.

Quasicrystals

Quasicrystals

e.g. rapidly cooled alloys

both short- and long-range

order

but incompatible with

translational periodicity

(e.g. 5-dimensional symmetry

seen in diffraction patterns)

Nanocrystals (quantum dots)

Nano-crystals

(quantum dots)

solids of

dimensions 1-

100nm

Many electronic

and mechanical

properties of

materials change

if they are

comprised of

nano-crystalsSEM of Nanocrystal of RuS2

Semiconducting Nanocrystal

26

Structure of solids

Elementary Crystallography

27

Important concepts

Lattices & Unit Cells

Simple Cubic Unit cells / Lattices

Crystal systems

Fractional Atomic Coordinates

Basic structure types

Elementary PXRD

Crystal Planes / Miller indices

d spacings

Braggs Law

Elementary structure & bonding in solids (1st year)

28

Lattices and Unit Cell

29

Unit Cell Dimensions

a, b and c are the unit cell edge

lengths

, and are the angles (a between

b and c, etc....)

30

Simple Cubic Unit cells / Lattices

Metallic

e.g. Po e.g. Au

e.g. Fe

31

Fractional atomic coordinates

The position of an atom within a unit cell is normally

described using fractional coordinates (in contrast to

orthogonal coordinates).

With respect to the unit cell origin, an atom within the unit

cell displaced by x a parallel to a, y b parallel to b and

z c parallel to c is denoted by the fractional coordinates

(x, y, z).

(0.5,0.5,0.5)

Slide 3211/05/2011

Fractional atomic coordinates and projections

The position of an atom in a unit cell is

described ito fractional coordinates.

Coordinates expressed as a fraction of the

length of the side of the unit cell.

Thus the position of an atom located at xa

parallel to a, yb parallel to b and zc parallel to c

is denoted (x,y,z), with o x,y,z 1.

Projections are often a clearer / faster method

of representing 3D structures.

Typically projections are down one of the cell

axies.

(a)The structure of

metallic tungsten

(b) Its projection

representation

Slide 3311/05/2011

Example 3.1

Projection representation of

fcc unit cell

The structure of silicon sulfide

(SiS2)

Slide 3411/05/2011

NaCl Rock Salt (Halite)

35

The seven crystal systems

36

Density of a crystal

Z = number of atoms in the unit cell

M = atomic weight

NA = Avogadros number

VC = Volume of the unit cell

cAVN

ZMdensity

37

Crystal Planes &

Miller indices

Since a crystal has an ordered 3-D periodic arrangement of atoms (ions

or molecules) the atomic planes in any crystal can be related to the unit

cell.

One can label each set of planes uniquely by considering their

(fractional) intersection with the unit cell axes a,b,c and converting

these to INTEGERS h, k, and l.

e.g. the planes that intersect the b-axis at and are parallel to a and

c. ( a/ , b/2, c/) are defined by the MILLER INDiCES (0 2 0)

See: (DoITPoMS), Lattice Planes and Miller Indices

38

Expressions for d-spacings in

the different crystal systems

Cubic

Tetragonal

Orthorhombic

Hexagonal

Monoclinic

Triclinic

2

222

2

1

a

lkh

d

2

2

2

22

2

1

c

l

a

kh

d

2

2

2

2

2

2

2

1

c

l

b

k

a

h

d

2

2

2

22

2 3

41

c

l

a

khkh

d

ac

hl

c

l

b

k

a

h

d

cos2sin

sin

112

2

2

22

2

2

22

Even more complex

39

Principles of XRDX-Ray beams collide with a solid and interaction with electrons of

the particular solid takes place. Interference is possible when the

wavelength of the incoming X-ray is comparable to the separation

between the atoms. When an ordered array of scattering centres are

present, the reflected X-rays will show interference maxima and

minima. Typical wavelengths used for X-ray experiments lie

between 0.6 and 1.9. Braggs Law

sindn 2

For CUBIC structures we can show that:

2222

22

4sin lkh

a

40

Structure and properties of

materials

Bonding in solids (REVISE) See S&A

Types and structures of solids (REVISE) See Atomic

Scale Structure of Materials (and do questions)

Basic Crystallography and Diffraction methods

(REVISE) See S&A, X-ray Diffraction Techniques

(DoITPoMS), Lattice Planes and Miller Indices

(DoITPoMS)

Mechanical properties of materials (Read Introduction

to Mechanical Testing (DoITPoMS) by next week)

41

End of Revision

Crystallographic databases

42

Database Contents / Components No. of entries

ICDD

www.icdd.com

PDF-2 / PDF-4 >150,000

NIST

www.nist.gov

Unit cell, symmetry & refs >200,000

Pauling File

www.paulingfile.com

Inorg. Ordered solids

ICSD Inorg. Cryst. Structures 64,734

CSD

www.ccdc.cam.ac.uk

Org. Cryst. Structures >260,000

Crystmet ~70,000

PDB ~20,000

COD