Metallic glass and its electrical resistivity

[y4ku24]

Hello guys.

My name is Luqman, and I am a new member of this forum. Currently studying in Japan on Metallic Glass/Glassy Metal/Metallic Alloy, which is a branch of solid state physics.

I have a million-dollar question though concerning metallic glass, which I would really appreciate if somebody could give me an answer (better still, a good website on the subject) to the question below:

I am relatively new to this subject, and it is like a common fact for metallic glass researchers that metallic glass` electrical resistivity DECREASES when the temperature increases. It is quite a weird phenomena, since normal metal`s electrical resistivity increases with increase temperature (because of the atom vibrations). As of now, the thesis and books I`ve read has taken this unique phenomena as a given, without explaining WHY it happens, in terms of the micro world. Does anybody know the answer to this?

I thank you all for helping me out!

 

[kanato]

Decreasing resistance with increasing temperature is a characteristic of semiconductors and insulators. The increase in temperature promotes electrons across the gap to the conduction band, increasing the number of charge carriers in the conduction and valence bands. I have never heard of metallic glasses. What are these made of?

 

[y4ku24]

Thank you for your concern.

Metallic glass is basically made of metal elements, but the structure in the micro level is amorphous, i.e. glassy. Thus the name metallic glass. How it is made is by rapidly cooling a melt so that the structure remains amorphous, even though it will return to its solid form.

It is a relatively new material. You can check for more info at wikipedia.

 

[Mapes]

I don't know much about the subject, unfortunately, but have you read Nagel's "Temperature dependence of the resistivity of metallic glasses," Phys Rev B 16(4), 1977, and the literature that cites it? Seems like a good spot to dive in.

 

[y4ku24]

No I haven't. Thanks for the info! The title of the book(?) is such kind of titles that I am really looking for! :D I will try to look for it at my library, but I don't know if they have it. Is there a site to read that or something?

 

[Mapes]

The library of any university with a science program should carry Physical Review B. You're looking for volume 16, issue 4, published in 1977.

 

[Enthalpy]

One possible explanation:

As nanocrystals are very small, electrons don't have a nice billiard pool to roll on (=energy band), but instead have to climb energy hills again and again. A higher temperature helps here.

I don't expect the model for semiconductors to apply here. It tells that conductivity is limited by the number of mobile carriers which improves with temperatures, but in an amorphous metal, I suppose mobile electrons are plentiful.

A slightly different explanation would be that in these tiny crystals, energy levels are still discrete, so thermal activation is needed to change the speed of an electron.

 

[f95toli]

There are several different phenomena contributing to the resistance in glasses so I don't think there is a single answer to your question.
At very low temperature the charging energy of the individual island becomes important and in some cases it is even possible to reach a state where the resistance goes up because of Coulomb blockade, one dramatic demonstration of this is the superinsulating state which was demonstrated a few months ago.
In the superinsulating state the resistance is huge (well, in theory infinite) since the
transport of charge carriers is completely blocked.

 

[y4ku24]

Thank you very much for all your wonderful insights! I am just a new member, but all of you have been much of help!

To Mapes: I have found the book and the specific chapter. Sadly, when it comes to explaining the strange phenomenon, it only says "There have been a number of theories attempting to explain this behaviour", without giving out some examples or even reference! :D

 

[Mapes]

y4ky24, that's a throwaway line from the first paragraph of the introduction. The entire paper is a proposed model for negative TCR! Several lines down, there's also a citation (Sinha 1970) for the idea of applying models of liquid metal resistivity to bulk metallic glasses.

Nagel's paper has been cited over 200 times and is still being used to explain resistivity trends today, so I conclude there's some validity to his model.

Thus, if I were studying the problem, I would follow these leads and try to find out why the resistivity of liquid metals decreases with temperature.