Ionic lattice structures

• high melting and boiling points

• only conduct electricity when ions can move

• huge lattice of ions

• ions held together by attraction of opposite electrical charges

• brittle when hit hard

Arrangement of ions in latticesdetermined by the relative sizes of the 2 ions

-ve (anion) larger

than +ve (cation)

e.g. sodium chloride

-ve (anion) and +ve (cation) roughly the

same size e.g. caesium chloride

Cs2+

Cl-

Other lattice structures

Zinc blende (ZnS)

Rutile (TiO2)

Ionic latticesWhich type of structure, CsCl or NaCl, are the following likely to have?

1. Lithium fluoride

2. Calcium sulphide

3. Potassium fluoride

4. Iron (II) oxide

Metals• good electrical conductorsgood electrical conductors

• some resistance to electron flow at normal temperaturessome resistance to electron flow at normal temperatures

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SuperconductorsH. Kamerlingh Onnes

• liquified helium in 1908

• investigated the low temperature resistivity of mercury

• resistance drops suddenly to zero at 4 K(-269oC) - critical temperature

Material T-Critical

Gallium 1.1 K

Aluminium 1.2 K

Indium 3.4K

Tin 3.7K

Mercury 4.2K

Lead 7.2K

Niobium 9.3K

Niobium-Tin 7.9K

LaBa2Cu3-oxide 30K

YBa2Cu3-oxide 92 K

TlBa2Cu3-oxide 125 K

InSnBa4Tm4Cu6- oxide 150 K

Critical temperature for Superconductors

Theory of Superconductivity

In cooled metals, ions do not spring back so quickly

The two electrons effectively travel as a pair

Metal ions in lattice vibrate as if attached by stiff springs

Positive ions are attracted to passing electrons

Ions quickly spring back after electrons have passed

Temporary local area of positive charge

A second electron is attracted to this area so follows the first electron through

Travelling as a pair, the electrons meet so little resistance that the metal can be considered to have zero resistance

Magnetic levitation

Superconductors are perfectly diamagnetic i.e. they

repel a magnetic field; this is called the Meissner

effect.

The Meissner Effect

More levitation!

Potential uses of superconductors

Transport

Maglev trains (Paris to Rome in just over 2 hours!)

Frictionless bearings increasing efficiency of electrical motors and generators in electric-powered transport

Smaller, lighter gyros in spacecraft and satellites

Potential uses of superconductorsMaglev trains

Maglev- Magnetic levitation trains which float over a guideway replacing steel wheels and tracks.

Frictionless so can travel up to 500km/h (310mph) – viable option replacing aircraft for some journeys.

China- Shanghai transrapid shuttles 19 miles from Pudong airport to Longyang train station in 8 min flat at 430 km/h

Potential uses of superconductorsMaglev trains

http://video.google.com/videoplay?docid=6261317600045015385

Main components to the Japanese system are:

A large electrical power source (a/c current)

Metal coils lining a guideway or track

Large guidance magnets attached to the train underside

The magnetic field created by the electrified superconducting coils in the guideway walls and the track combine to levitate it 1-10cm.

Potential uses of superconductorsMaglev trains

How it works.

Guideway for the Yamanashi maglev test line in Japan.

Potential uses of superconductorsMagnetic Resonance Imaging (MRI) - non-invasive imaging of parts of body

Uses a superconducting electromagnet to produce a magnetic field x10,000 stronger than the earth’s

The electromagnet wire is made from a superconducting Niobium-titanium alloy is cooled by liquid helium (4K).

Machines cost around £500,000 and have high running costs but most large hospitals in the UK have one.

Potential uses of superconductors

Power transmission - reduce energy lost as heat (currently up to 10%)