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Re: metal conductivity



At 05:44 AM 2/8/00 -0500, John Cooper wrote:

> Can anyone explain, on an atomic level, why copper and silver are better
> conductors of heat and electricity than the other transition metals?

I'm not sure I understand the point of the question.

The wording of the question rather implies that there is an important
difference between copper and silver on one hand, and the other metals
(say, aluminum and gold) on the other hand.

From my perspective, it is more important to note how similar all these
metals are -- not how different they are.

According to page 562 in my copy of Ashcroft & Mermin, typical metals have
resistivities around 10^-6 ohm-cm, while undoped semiconductor materials
can easily have resistivities fifteen orders of magnitude larger than that,
and serious insulators are maybe 28 orders of magnitude more resistive than
metals.

Also, according to page 8 (op. cit.) at zero C we find 13 of the 26 metals
on the list have a resistivity between 1.5 and 8.55 microhm cm. Such info
is available on the web, too; see e.g.
http://www.webelements.com/webelements/elements/text/phys/Ag.html

Thirdly... suppose you want to run a wire from point A to point B and you
are limited as to _weight_. Then aluminum will give you a much lower
resistance than copper.

========

So my basic answer is that they're all about the same, with small
variations. "At the atomic level" there are scads of reasons why there
should be small variations. Due to these variations, _some_ element has to
win the contest, but don't look for an explanation of the qualitative
difference because there isn't a qualitative difference.

---

If you want the next level of detail, you can sign up for a year-long
graduate course in solid-state physics. That will cover such things as
-- the band structure, which in turn depends on the crystal structure
-- the number of electrons available, leading to full, empty, and (most
importantly) partially-full bands
-- the thermal phonons, which at room temperature are the dominant
physical process causing resistivity in metals

At the level beyond that, if you want to start with basic definitions
(copper = element 29; gold = element 79) and then calculate _ab intio_ "on
the atomic level" their resistivities... that would be considerably beyond
the state of the art.