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A new discovery made in thermoelectrical crystal compounds helps explain heat conduction at the molecular scale.

Though thermoelectric materials are quite common, they are not yet widely used as one might expect. The reason is largely that until very recently, these materials have been either very inefficient or very expensive. However, several groups of researchers have been working to solve the mysteries of these exotic compounds and bring them to the world en masse.

DailyTech has previously reported on a few endeavors with thermoelectrics. Mildred S. Dresselhaus's ongoing work at the Massachusetts Institute of Technology looks to create more efficient materials by manufacturing tiny particles or wires into them to disrupt the flow of heat. This would make materials that are already great electrical conductors much more thermally inert, allowing for greater heat-to-electricity or electricity-to-heat/cold conversion potential.

Another group at the University of California at Berkley, led by Professor Peidong Yang is looking into new materials. Silicon itself is not a great thermoelectric material – until venturing into nanoscale. Silicon nanowires have been shown to be one hundred times more efficient at the energy conversion than bulk silicon.

Publishing its findings in the most recent issue of Nature Materials, a group of scientists from the University of Århus, Risø-DTU and the University of Copenhagen has unlocked another secret of certain thermoelectric compounds which may help develop more efficient materials. Their work involves clathrate compounds, which are compounds composed of a “cage” of one type of molecule that surrounds a second type.

Initially it was believed that the movement of the trapped molecule was solely responsible for the way the compound conducted heat. After using neutron scattering to study the movement of the atoms inside the molecules, they realized it was the movements of the atoms in the cage that brought about the advantageous property.

Kim Lefmann, an associate professor of the Nano-Science Center, Niels Bohr Instituate at the University of Copenhagen explains, “Our data shows that, it is rather the atoms' shared pattern of movement that determines the properties of these thermoelectric materials. A discovery that will be significant for the design of new materials that utilize energy even better.”

Understanding the mechanism behind this thermal insulation will help scientists design better thermoelectric materials. These types of materials are finally being put to use in some of the places you might expect, such as vehicle auxiliary power generation from waste heat. The same waste heat could theoretically be used to power interior cooling systems via heat to energy to heat (and cooling) transference.

Thermoelectric materials have a tremendous amount of potential for use in everything from vehicles to homes and businesses to electronics. Better understanding of how these materials work will spawn more efficient materials and perhaps one day these things will be powered, cooled and heated by super thermoelectric devices.

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Pinky calling for the Brain.
By Mitch101 on 10/8/2008 3:59:10 PM , Rating: 2
Can someone explain to me when an electron moving through a electronic circuit produces more heat at a slower speed than say a photon moving through a fiber optic cable at a significantly higher speed? By slower speed I am referring to electrical current compared to the speed of light.


RE: Pinky calling for the Brain.
By Lankym on 10/8/2008 4:26:06 PM , Rating: 3

RE: Pinky calling for the Brain.
By soydios on 10/8/2008 4:59:29 PM , Rating: 4
Number of collisions. That electron collides with a lot of the conductor's molecules as it drifts.

RE: Pinky calling for the Brain.
By menace on 10/9/2008 2:10:43 PM , Rating: 2
It has more to do with the force interactions with the other electron and nucleii. Photons to not carry any charge or weight and are able to move through a transparent medium with negligible energy transfer. Pushing EM waves through wires (via the electrons present in the medium) results in a small but significant portion of the energy being transfered into the wire. The heat conversion surely has to do with quantum mechanics but I'm not smart enough anymore to explain how.

By the way, the electrons themselves don't move across a wire at relativistic (near light) speeds but the energy they transfer across the wire does. And this is true regardless of if the current is AC or DC. A good analogy is to envision a long pipe full of ping pong balls. If you push one ping pong ball at one end, a ball immediately pushes off the other end even though no single ball moved more than the diameter of a ball.

RE: Pinky calling for the Brain.
By amanojaku on 10/9/2008 3:37:05 PM , Rating: 3
Exactly. One physicist pointed out that a human can run faster than an electron can move, unless that electron is infused with energy from an external force. Unless the electron jumps up a valence shell, eventually escaping the atom to become a free electron, the energy is converted into a different type, like heat, light, etc...

The energy that moves at light speed (in a vacuum) is the electromagnetic field. When traveling through a medium the speed moves at less than light speed, determined by the atomic composition. With the right atomic composition the electric field can move at speeds approaching light in a glass silica fibre. It will still generate a lot of heat, however, and is subject to electromagnetic interference, unlike light.

RE: Pinky calling for the Brain.
By Black69ta on 10/8/2008 5:09:09 PM , Rating: 2
Weight: Photons are much lighter than electrons, Electron don't travel in a straight line but more like water particle in an ocean wave. Photons in a fiber optic cable are generally produced from a laser which makes them uniform and in phase. thus the don't collide as much and when they do the energy involved is much less.

RE: Pinky calling for the Brain.
By Chemical Chris on 10/8/2008 5:27:35 PM , Rating: 3
Photons don't weigh anything, actually.
And are they particles, or waves...both you say, well....alrighty then, i guess
I think the current idea is something along the lines of they are too small (or are just unable) to interact with the Higgs field that permeates everything.
Of course, we should know if thats a credible theory next year.... gotta hate it when there's ~9999 good soders, and 1 bad soder job brings down the whole $9 billion LHC :(
But I digress, photons, very small, have no mass, but have energy (which violates e=mc2, but so it goes)

RE: Pinky calling for the Brain.
By Integral9 on 10/9/2008 8:52:14 AM , Rating: 2
I'm pretty sure photons have been proven to have mass. An incredibly small amount of it, but some. The solar sail theory is based on it and I think it was proven correct. Anyone?

RE: Pinky calling for the Brain.
By theapparition on 10/9/2008 10:36:25 AM , Rating: 2
Photons have no mass. None.

Solar Sail theory is based that even though photons don't have mass, they do carry momentum.

RE: Pinky calling for the Brain.
By geddarkstorm on 10/9/2008 1:49:35 PM , Rating: 2
Which means photons must have an inertial mass: p=mv where p is momentum, m is mass and v is velocity. Arthur Holly Compton showed this when studying x-ray diffraction, where the x-ray quanta have momentum proportional to their frequency (the higher the frequency, the more the wave "moves" over the same distance, which would give it an increased velocity for the particle, or photon, aspect).

So, as someone else pointed out, light has no resting mass (if it isn't moving it doesn't exist), but has relativistic (inertial) mass.

RE: Pinky calling for the Brain.
By Adonlude on 10/13/2008 5:27:15 PM , Rating: 2
NOPE. The simple answer is that after several thousand years we have not yet managed to assemble a system of thought and calcualtion that encompases life, the universe, and everything.

I predict we will one day build a computer that operates not in base 2 but in base 42 and through simulation we will finally figure it out. The symbols utilized in this base 42 computer will be 0-9 (look at your hands) as well as the 32 symbols of the ancient Ugaritic Alphabet. These 42 symbols form the original foundation of human communication.

RE: Pinky calling for the Brain.
By theapparition on 10/9/2008 10:35:16 AM , Rating: 2
Photons don't violate E-mc². The equation only serves to relate mass and energy.

RE: Pinky calling for the Brain.
By Chemical Chris on 10/9/2008 11:16:16 AM , Rating: 2
energy = mass * speed of light^2
so, if it has energy, but no mass, you get:
real number = 0 (ie, 5=0)
clearly, a real number cannot equal 0. So, yes, it sure appears violated to me. If it has mass, it must have energy, and if it has energy, it must have mass. Please correct me if Im wrong (with some evidence, not just 'because i said so', if im wrong, then i get to learn something :)
I can see how it "isnt violated", in that a photon with energy can be destroyed to create mass, or that mass can be destroyed to create a photon, which is true. Its also a part of how nuclear weapons work (a small amount of mass is converted to energy; while no large subatomic particles are destroyed, some of the 'gluons' in the nucleus are destroyed. That is, the mass of subatomic particles and atoms generated from fission/fusion have less mass than their original atom. All atoms 'lose' a small fraction of mass relative to their component parts, called the 'nuclear packing fraction", ie, even though Oxygen has 8 protons and neutrons and should weigh 16, its actually (IIRC) 15.994 (real mass for O-16, not average of all O isotopes)

RE: Pinky calling for the Brain.
By amanojaku on 10/9/2008 11:49:04 AM , Rating: 2
You might want to check your facts.

In physics, mass–energy equivalence is the concept that for particles slower than light any mass has an associated energy and vice versa. In special relativity this relationship is expressed using the mass–energy equivalence formula E=mc^2

A photon has a rest mass of 0 and therefore does not violate mass-energy equivalence. Its relativistic mass is equal to its energy, E/c^2.

RE: Pinky calling for the Brain.
By amanojaku on 10/8/2008 6:22:27 PM , Rating: 2
Electrons have mass, photons don't. Any particle that has mass can vibrate, and vibration requires a great deal of energy, resulting in a great deal of heat being transferred. Photons have no mass and transfer heat through radiation (photons are carriers of electromagnetic radiation.)

An electron is capable of emitting a photon when it looses energy. So you could over simplify and say an electron is capable of carrying more energy than a photon, and therefore transfer more energy as a result. On the other hand, an electron can absorb photons and the photons' energy. When that happens the electron can:

1) Move farther from the atomic nucleus until it escapes orbit
2) Emit one or more photons (and energy)
3) Transfer heat

RE: Pinky calling for the Brain.
By amanojaku on 10/8/2008 9:55:22 PM , Rating: 2
FYI, a common misconception about the "speed of electricity" is that electrons flow through a conductor at less than the speed of light. This is true, but doesn't explain how electricity is transferred over a wire. It is the electromagnetic field that propagates at or less than the speed of light and transfers a signal.

The electromagnetic field is a force (vector): it has a magnitude and a direction. The proximity of moving charged particles (quarks, the negatively charged leptons, and the W force boson) create vector fields that affect each other. This interference (made worse by increased density of charged particles) is what reduces the speed of propagation of an electromagnetic field. It is theoretically possible, but practically improbable, for electromagnetic fields to align naturally in the same direction.

This is a gross over simplification of the nature of physics. Anyone describing the slower speed as a result of electrical resistance or the collision of electrons is wrong.

RE: Pinky calling for the Brain.
By Xajel on 10/9/2008 7:45:36 AM , Rating: 2
Electrons are :
- charged, they will have some resistance with other electrons in what ever they go through, this resistance will force the electron to not walk in a direct line, but rather some wavey line do to alot of attoms in the way.
- big and heavy, they will hit some attoms in thier way, of course hitting doesn't mean touching as this will need impressive amount of energy for that electron as the atom is self is covered with a cloud of electrons over the core.

Photons :
- non charged, photons doesn't have a charge like electrons, so they just walk fast in that matter.
- small and mass-less, photons are much much more smaller than even the electron it self, so they wont hit the electron cloud but they will penetrate the atom it self, and duo to the fact the atom has more than 95% of it's size just an empty space, photons can easly go throught it...
- it's interaction with materials in the fiberoptics, to a photon, fiberoptics are transparent, so they're designed to let as much as photons as possible, not 100%, but more closely to 95% - 99% depending on the quality, so the natural of fiber optics is similar to some near-vacume to electrons, of electrons are traveling trought a vacume, they wont hit any thing, so it will be something like transparent to them, ofcourse having a 100% vacume is too diffecult and hard as you have to make sure there's not even any atom in that space, even in the very deepest space they said it has 1 atom per cubic cm and that atom is H2 or He2 as they're the most common attoms in the known universe...

"The whole principle [of censorship] is wrong. It's like demanding that grown men live on skim milk because the baby can't have steak." -- Robert Heinlein

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