Transcript Ionic structure, semi- and super-conductors

Face centred cubic lattice
e.g. NaCl
Single unit cell
Sodium chloride has the
coordination number 6:6, as the
sodium ion has six neighbouring
chloride ions, and visa versa.
Body centred cubic lattice
e.g. CsCl
Single unit cell
Caesium chloride has the coordination
number 8:8, as the caesium ion has 8
neighbouring chloride ions, and visa
versa.
What are they?
Superconductors
are can
materials
Superconductors
be
Ceramic
materials,
such
as no
whichalloys
conduct
electricity
Metal
metal
such
elements
as niobium-titanium.
likewith
magnesium
loss of
energy. They
have zero
mercury
ordiboride.
silver.
resistance.
Superconductors were, in the past,
impractical because they had to be
super cooled by liquid helium which
scientists were complaining was
“Really deer to buy.”
=
Ceramic superconductor’s critical
temperature for superconductivity isn’t
as close to zero degrees Kelvin, which
means liquid nitrogen can be used in
place of helium. This is less expensive.
In a weak applied field, a superconductor
"expels" all magnetic flux. This allows a
magnetic object to “float” above a
superconductor.
Scientists have come to the conclusion
that this effect is “pretty class”.
Material before
cooling
Material after cooling,
in superconductive
state
Arrows represent magnetic field lines
Power Cables:
Right
Using
now,
a superconductor
up
10% of
electrical
could
energy
It would
alsotoallow
power
lineseliminate
to
be
carried by
power
this underground.
energy
cables loss.
is lost as heat
hidden
Other uses include:
Magnetic Resonance
Imaging
Superconductors create
high magnetic fields,
this allows doctors to
see inside parts of the
body that hitherto had
not been visible outside
of investigative surgery.
Electronics
Using superconductors to craft
electronic switches could advance
microprocessor technology
making them extremely fast.
Other uses include:
Transport
Oh,
and may
that car
fromtoI, hover
Robot
Trains
be able
over tracks which means
frictionless, high speed
travel like the Maglev Train
in Shanghai, China.
Semiconductors are materials that have a
conductivity lying somewhere between
non-metals which have no free charged
particles, and metals, which have free
moving electrons.
Their conductivity
increases with
temperature and
exposure to light.
Examples are silicon
and germanium,
metalloids that have
four valence electrons.
Ga
N-type
P-type
Ga
Ga
Si
Ga
Ga
Free electron
In an n-type conductor, an
impurity from group five such
as antimony or arsenic is
added to a group four
semiconductor, four bonds are
created leaving one free one
to act as a charge carrier.
Ga
Si
Electron
Ga
Ga
Positive hole
In a p-type semiconductor,
and impurity from group
three such as gallium or
indium is added, this creates
three bonds with the group
four semiconductor leaving a
gap where an electron should
be. This is known as a
“positive hole” as it contains
no negative electron.
When light
energy falls on a
semiconductor,
the conductivity
increases.
The energy a
photon delivers to
an electron
releases it from
n-type side of the
junction and the
depletion layer
causes a potential
difference.
P-N Junction
N-type
-
-
P-type
+
-
+
-
Depletion layer
+
+
+
+
+
Magnesium chloride has the same
Which of the following statements
referring
to as sodium
coordination
number
the structures of sodium chloride
and caesium
chloride.
What shape is the
chloride is correct?
magnesium chloride crystal?
A: There are eight chloride ions
surrounding each sodium ion.
Answer B:
caesium chloride
Answer:
is a body centred
Sodium
chloride
has
B: There are eight chloride ions
lattice with a
a coordination
surrounding each caesium ion.
coordination of
number of 6:6, like
8:8.
sodium
chloride,
C: The chloride ions are arranged
magnesium chloride
tetrahedrally round the sodium ions.
is a face centred
lattice.
D: The chloride ions are arranged
tetrahedrally round the caesium ions.
Explain the Meissner effect.
A superconductor is a material
A : Whose electrical conductivity decreases
Answer C:
Answer:
with decreasing temperature
Superconductors
When cooled below a critical point, that are cooled to
a superconductor
B: That does not conduct electricity
unless repels all
extremely low
doped with another materialmagnetic flux, this allows a temperatures past a
magnetic object to “float” above it. critical point can
C: That can conduct electricity with zero
conduct electricity
resistance
with no energy loss.
D: Whose electrical conductivity increases
with increasing temperature.
How does a photovoltaic cell convert light energy into
electricity?
Silicon can be converted into an n-type
Answer:
semiconductor by adding
Photons release
electrons, they gather
A: Boron
at the p-n junction and
form a depletion layer
B: Carbon
creating a potential
difference.
C: Arsenic
D: Aluminium.
Answer C:
Using a group
five element
like arsenic to
dope silicon
will leave one
free electron
turning it into
an n-type
semiconductor.