Dielectrics- Key Features

Question 1

What are dielectric materials used for?

Answer 1

Multilayer ceramic capacitors (MLCCs)
Pyroelectric sensors- for detecting heat changes
Piezoelectric sensors- for sonar technology
Piezoelectric actuators- precision movement in complex electronics
Piezoelectric ignition- common gas burners

Question 2

Key material properties of dielectric materials

Answer 2

ferroelectricity, pyroelectricity, piezoelectricity

Question 3

What are people trying to improve about dielectric materials?

Answer 3

Substitution- reducing/removing polluting, toxic or rare elements from their composition
Energy- reducing the energy waste in electronics
Manufacture- designing cleaner and cheaper manufacturing processes
Performance- operating with greater ranges and in more environments

Question 4

3 key features of dielectric materials

Answer 4

They are electrical insulators at 298K. They belong to non-centro-symmetric point groups. They possess or develop polarisation

Question 5

What does it mean when dielectrics are insulators?

Answer 5

Have resistivity>10^8 ohm.cm
No long range migration of electrons, holes or ions
Electrons/holes are localised in strong covalent bonds or restricted close to atomic nuclei (ionic bonding)
There is a band gap between the valence and conduction bands.

Question 6

What does it mean when dielectrics belong to non-centro-symmetric point groups

Answer 6

They have no inversion symmetry. there is no central point through which if all the atoms are inverted you end up with the same structure. Most cubic structures have inversion symmetry. Tetrahedral ones don’t.

Question 7

What does it mean when dielectrics possess or develop polarisation

Answer 7

There are dipoles in the material. This is when there is a charge imbalance because more charge is on ones side of the cell than the other. There is then a dipole moment vector, p equal to qxd. q is charge and d is separation between the charges.