Ionic Lattices, Superconductors And Semiconductors Flashcards
What is the coordination number?
The number of nearest neighbours by which an atom/ion is surrounded in a structure.
What are the properties of ionic compounds and what do they depend on?
Brittle solids at RT, have high melting/boiling points and conduct when molten/dissolved.
Depends on it’s ionic lattice structure
What are the two tubes of ionic lattices? And how do you know if it is one of these?
Face centred cubic structure (fcc) and body centred cubic structure (bcc) .
If the ionic radius for the positive ion ➗ the ionic radius for the negative ion is close to 1 = bcc, if it’s less than 0.75 then = fcc (as it will fit in centre).
What are superconductors?
A metal/alloy which at a certain temperature (around 0K) when cooled down had zero resistance- it conducts completely.
What do superconductors allow?
The current to be carried without any loss of energy
Why do superconductors have a no. of potential uses?
Due to their zero resistance and because they repel a magnetic field. This causes a magnet to levitate above it’s surface- the Meissner effect
Give 4 potential uses for superconductors
1) frictionless transport systems - trains electromagnetically levitated above the track and run at a high speed due to lack of friction
2) power transmission - energy loss prevented, wires could then be hidden underground, removing pylons from the environment
3) MRI - superconductors create high magnetic fields which allow images of parts of the body where investigative surgery may have previously been required
4) electronics - fast electronic switches could be made leading to ultra fast microprocessors
What are semiconductors?
Half conductors.
An element that has a very low conductivity at RT but whose conductivity increases with increasing temp/ the addition of certain other elements.
Part of the metalloids (nearly metal)
What can affect semiconductors conductivity ?
It increases with exposure to light.
It can be affected by the presence of impurities.
What is doping?
The deliberate addition of impurities
What does a semiconductor promote?
The electrons into the conduction band. Increasing temp gives more energy to move electrons into it
What are the two types of doping and explain?
P type, produces a positive hole. Putting in an element with too few electrons- starves a neighbouring atom of a bond.
N type, putting in an element with extra electrons which leads to ‘spare’ bonds and more electrons become available for conduction. Therefore the conduction of a semiconductor increases.
What does increasing temperature do in doping?
Free more electrons
What is a p-n junction?
When a piece of n-type is layered onto a piece of p-type which creates a barrier to electron movement at the junction.
Electrons move across to fill positive holes and form a barrier. Therefore electrons can’t flow/fill positive holes anymore. Electrons then must flow through an external circuit to fill them. Moving electrons=conductivity.
