ACII-Part II: Structure of solids; Structure-properties

relationship Dr. Liliana Viciu

1 ACII: Prof. Reinhard Nesper and Dr. Liliana Viciu

Liliana Viciu B. Sc. and M.Sc. at University of Bucharest, Romania

Ph.D. at University of New Orleans, USA

2

Contact info: Office HCI – H101 e-mail: liliana.viciu@inorg.chem.ethz.ch Tel: 044 632 6743

TOPICS

1. Properties we see in solids

2. Basic crystallography

3. Introduction to crystals symmetry

4. Diffraction on crystals

5. Important crystal structures in solid state chemistry and properties associated with them

3

Bibliography

1. Anthony R. West: Solid State Chemistry and its Applications

2. Ulrich Müller: Inorganic Structural Chemistry (online book through ETH library)

3. Martin Bürger: An introduction to fundamental geometric features of crystals

4. Werner Massa: Crystal Structure Determination

4

www.ac.ethz.ch username: ”aach” password: “jsenpw”

Slides on:

Syllabus

5

•The type of properties we see in solids; •Solids classification based on bonds and atomic arrangement • Basic Crystallography (Bravais Lattice; Crystal lattice; crystal structure; counting atoms; crystal density; packing density; characteristic of cubic systems); • Symmetry concepts: symmetry operations; symmetry in 2D; plane groups; symmetry in 3D; space groups and some examples of symmetry applications •Lattice directions; lattice planes – Miller indices; Diffraction on lattice planes; constructive and destructive interferences; systematic absences; patterns indexing •Packing of atoms: properties of solids explained by packing; voids in close packed structures; structure build by space filling polyhedral; •Important structure types: close packed structures and non-close packed structures

6

Solid Materials in our daily life

7

Materials development in early civilizations

• Stone Age (2.5 million BC)

• Bronze Age (3500 BC)

• Iron Age (1000BC)

Materials Types

• metals (metals and alloys)

8

• ceramics (oxides, nitrides, carbides, glasses, concrete)

• polymers (plastics, rubbers)

• composites (fibers)

Advanced Materials • semiconductors for sophisticated electronic devices

(i.e. energy conversion)

• energy storage (batteries, ultracapacitors)

• thermoelectric materials

• magnetic information storage

• optical fibers and piezoelectric materials as sensors 9

Solid state chemistry

• Development of materials: synthesis, structure, and properties

• Understand the relation between structure and properties

10

11

12

1. Nontoxic, unreactive with the beverage 2. Barrier to CO2 passage 3. Mechanical strength 4. If optically transparent retain its optical clarity 5. Ease of fabrication 6. Low cost

Identifying Properties

The response of a material to an external stimulus

13

Type of external stimuli:

1.Deformation 2.Electrical field 3.Temperature 4.Magnetic field 5.Light

1. Deformation Mechanical properties

14

http://www.clipartof.com/gallery/clipart/gold_people_2.html

• elastic deformation (reversible) stiffness

http://graphtechsblog.com/?p=108

• plastic deformation (irreversible) strength, hardness, malleability and

ductility

Deformation = the ability to change the shape when load/forces are applied

Malleability and ductility of some metals is understood by their close packed structures:

cubic close packed (ccp or fcc) > hexagonal close packed, hcp, structured > body centered cubic (bcc)

15

*

* Nb is an exception!

2. Electric field Conduction properties

16

2.1. Ionic Conductors

2.2. Electronic Conductors

Insulators Semiconductors

Metals Superconductors

Conduction = ability to conduct charge through a solid

• conduction through cations (NaCl –type solids) ex: NaCl, MgO,

- Li3N, AgI

• conduction through anions(CaF2 – type solids) ex: ZrO2 stabilized with CaO or Y2O3

17

Batteries = energy conversion + energy storage Solid oxide fuel cells = energy conversion http://www.gepower.com/research/seca/sofc_research.htm

Charge migration or charge diffusion increases with temperature

2.1. Ionic Conductors

The flow of electrons/holes throughout a solid

18

2.2. Electronic Conductors

Insulators Semiconductors

Metals

Solid Electrical Conductivity (Sm-1)

Ag Cu Al Graphite Si Ge GaAs Diamond

6.1x107

5.9x107

3.7x107

7.3x104

4.4x10-4

1.1x10-5

10-6

10-11

netyconductivi ,

e = charge (constant; independent of temp.) = mobility of carriers (decreases slightly with increases of temp.) n = nr of charge carriers

• Metals no band gap

• Eg 3 eV semiconductor (i.e., EgSi = 1.1eV)

• Eg > 3 eV insulator (ex Egdiamond = 5.4eV)

19

Band gap in solids Electronic conduction explained by energy band theory

Solid Band Gap Eg (eV)

Structure type

Diamond Si Ge InSb GaAs

5.4 1.1 0.72 0.82 1.34

Diamond Diamond Diamond Zinc blende Zinc blende

• Resist to the flow of electric charge

• Have large band gaps (Eg>3eV) (capacitors)

• Dielectrics (change in polarization with an applied electric field)

20

R. Tilley: Understanding solids, The science of Materials, J.Wiley &Sons,2006

surface charge due to the internal dipols formation =

polarization, P

In some dielectrics change in polarization arises from mechanical stress

piezoelectric

In some piezoelectrics change in polarization arises from change in temperature pyroelectric

In some pyroelectrics the polarization is easily switched in an electric field

ferroelectric

Insulators: Dielectrics

Structures with no inversion center could show piezoelectricity

ex: structures with Td groups like ZnS-zinc blende (sphalerite) and ZnS-wurtzite type structures)

Perovskite structures with d0 transition metals show pyroelectricity and even ferroelectricity

21

Examples of Dielectrics Piezoelectrics: quartz resonators, power generating floors, lighters, etc

22

Pyroelectrics: temperature sensors, power generation

Ferroelectric: capacitors, ferroelectric RAMs

a. Ferroelectric b. Anti-ferroelectric c. Ferroelectric polarization

a b c

23

kTEge /~

Mobility, , increases with molecular weight and decrease with electronegativity difference (polarization effect of mobile electrons or holes on the surrounding atoms)

Semiconductors Conductivity increases as temperature increases the carrier concentration, n, increases as temp goes up due to excitations across the band gap, Eg)

Eg (band gap)

Valence band

Conduction band

Conductivity of a semiconductor will increase exponentially (up to a point) with an increase in temperature!

Semiconductors have often diamond or ZnS –blende (sphalerite) structure.

Due to the covalent character of its bonding interaction (the lattice is always composed of those elements with the smallest difference in electronegativity).

24 4/10/2013 L.Viciu| ACII| Imprtant structure types

Examples of semiconductors at work

25

the center of solid-state electronics: Si, Ge, Sn, III-V compounds (GaAs, InSb ) and II-VI compounds ( CdTe)

Solar cells (photovoltaics)

Conductivity decreases with increasing temperature

26

Metals

the number of charge carriers, n, do not vary with temperature (higher energy levels are still in the valence band)

ne

Valence band

Conduction band

No Eg, (band gap)

Mobility, , decreases with increasing temperature (the lattice vibrations will scatter the electrons – collisions with the crystal lattice)

Examples of metallic conductors

27

•NiAs - type compounds (not layered structure) and often in layered structures (MoS2, graphite) where orbital overlap is enhanced on certain directions (z direction vs xy plane) show metallic conduction

Solid Electrical Conductivity (Sm-1)

Ag Cu Al Graphite

6.1x107

5.9x107

3.7x107

7.3x104

• In the superconductivity state no electrical resistance - the current will flow forever without diminishing

28

SC- type I: mobile electrons in pairs Cooper pairs SC – type II: High Tc superconductors cuprates, MgB2, Fe-based superconductors – mostly layered structures

Superconductors

Superconductors at work

29

MRI

NMR Maglev BMRI = 30 000 gauss

BEarth =0.25–0.65 gauss

3. Temperature Thermal behavior

30

•Thermal conduction = attributed to the mobile electrons (in metals) and phonons in ceramic materials Ex: diamond, BN, SiC

•Thermal expansion and contraction Ex: memory shape alloys (CuZnAlNi, CuAlNi, NiTi=nitinol) used in medicine and aerospace

•Thermoelectric effects: combines thermal conduction and electronic conduction

4. Magnetic field Magnetic Properties

31

Each electron has a magnetic moment due to the existence of a magnetic dipole (electron spin) (a) diamagnetic materials (repealed by a magnetic field) (b) paramagnetic materials (attracted by a magnetic field)

Spin interaction in paramagnetic materials ferromagnetic(i) and antiferromagnetic (ii) materials

(i) (ii)

• Perovskite materials with dn transition metals

• Spinel structure with magnetic ions such as Fe, Co, Ni, etc

32

• Spintronics devices: MRAM, sensors, spin transistor, spin memory

33

Electron flux through a

ferromagnetic layer

Ex: Mn doped II-VI and III-V semiconductors; GaAs; Co doped TiO2

• Information storage, transformer cores, permanent magnets

Ex: Fe2O3, Co, Ni- based materials, yttrium iron garnet (YIG=Y3Fe5O12)

Applications of magnetic materials

5. Light = Optical properties

• Color and appearance (selective absorption)

• Refraction and dispersion (apparent bending and separation of white light)

Ex: diamond

• Reflection (change in direction –return to the medium)

• Scattering (spreading from straight trajectory)

Ex: blue moon stone

• Diffraction (apparent bending of waves around small obstacles and the spreading out of waves past small openings) 34

dispersion

35

Composition

Structure

Properties

Performance

Design and construction

Solid Materials Package of Properties

Properties f(composition)

Properties of Materials

Choice of composition + Crystal Structure

36

• Solid properties = f(Composition)

• Solid properties = f(Atomic arrangement)

Ex: diamond vs. graphite

Composition alone can’t give the properties of a material, they are dependent on the atomic arrangement.

37 pictures from wikipedia

Solid State Chemistry

• Electronic structure of the elements holds the key to the understanding of the long range atomic order in solids;

• Electronic structure of the atomic constituents and symmetry arguments are the criteria for the material selection process

38

39

Interatomic bonding 3D- atomic arrangement

Crystal structure

Symmetry arguments

40

Interatomic bonding 3D- atomic arrangement

Crystal structure

Symmetry arguments

Material selection process

1. What atoms are involved and their electronic configuration?

2. What types of chemical bonds are formed?

3. How are the atoms arranged in the crystal structure?

4. What is the symmetry of the crystal?

5. Do these arrangements promote certain mechanisms for

electronic or atomic motions?

6. How do these mechanisms give rise to the observed properties?

41