Comprehending Thermoelectrics

I am in Baton Rouge, Louisiana! The South!!

I’m here for 10 weeks for a REU (Research Experience for Undergraduates) program. I get paid to learn physics and have fun!

To really make it short, I will be creating supercapacitors. A capacitor is something that holds a charge. But this is a supercapacitor. Meaning this capacitor will hold a lot of energy. So imagine your phone. “Agh.. out of juice. mrmmm.. time to charge this hunka chunka.” It takes quite a while to charge smartphones. But with a supercapacitor, you will be able to fully charge your phone in less than 30 seconds. The whole world of batteries and energy storage would be revolutionized. Electric cars, plug in, plug out, and it would be ready to go in minutes.

But how does one come about making a supercapacitor?

I will be using a DVD drive/burner and using a laser software to create thin film graphene from a DVD coated with graphite oxide. This is a process recently discovered by a couple UCLA researchers. However, my project will have its own spin and I’ll have no idea how it will turn out. In fact, I may not even reach the synthesis part because my project’s spin requires quite a bit of effort to synthesize the prerequisite materials. I will write the details of the experiment after the REU.

The general topic of my research can be called numerous things: Solid State Physics, Condensed Matter Physics, or more broadly Materials Science.

The title of this post is called Thermoelectrics because today Dr. Young, the professor I am working with, gave me a two hour crash course on thermoelectrics. Dr. Young is a tall masculine man with an overtly stating voice and an endless grin on his face. (My attempt at describing people in the style of George Orwell! 1984..) Thermoelectrics involve obtaining a charge from heating up say copper. So imagine heating up one side of a solid copper cylinder with a torch on one side. One side will get really hot! (The side with the torch right below it) But the other side will be slightly less hot. This creates a heat gradient. This gradient actually causes a voltage or electric potential difference. So if you were to connect the copper to a volt meter, you would actually measure a voltage (Vc). For copper, it would actually be a horrible thermoelectric material because it conducts heat so well. What you need is something that is absolutely horrible at conducting heat, something like quartz! Meaning if you were to heat up one side of quartz, it feels near room temperature if you were to hold it on the other end.

How good a material is for thermoelectrical applications depends on a variety factors. There exists a figure of merit that details thermoelectric materials and their ZT values. The bigger the ZT, the better. T is temperature and Z is comprised of electrical resistivity, Seebeck coefficient, and the total thermal conductivity. (Z = (S^2/rho*kappa) That’s a whole lot of names and labels!! But the gist is that every material has values for these properties and the bigger the Z the better. And the challenge in science right now is by changing one of those values, we adversely change another. So to increase Z is actually very difficult!

Doping is one way to change our value of Z. Imagine a FeSi compound. FeSi is a nonmagnetic insulator. Now if you look at a periodic table and move one element to the right, we arrive at Cobalt. Because of iron’s proximity to cobalt, we can say they are quite similar. So now lets say we have CoSi compound. CoSi is a diamagnetic metal (nonmagnetic conductor). So both of them are nonmagnetic. But now lets introduce Fe(1-x)Co(x)Si. By adding a little cobalt into our FeSi, magnetism appears!

All this sciency talk is weird! Just a year ago, I was scared of physics. But now, it’s one of the best things to happen to me.

My goal for these ten weeks is to synthesize the supercapacitor. It will be interesting to see what properties the capacitor I will be making will have. Till the next entry!