Re: metal conductivity (fwd)

[brian whatcott <inet@INTELLISYS.NET>]

> Leigh Palmer wrote:
>
> > ...What is responsible for making a
> > material a good conductor of electricity or heat?...
At 11:30 2/8/00 -0500, Ludwik responded:

> My answer to this "better question" is that the number of free
> electrons per cubic centimeter is the decisive factor.
> ... [Some "crystal corridors" may be more resistive than others.]

> Ludwik Kowalski

Ludwik's anisotropic resistivity suggestion brings to mind the
preferred direction of conduction in polyacetylene plastic - which
betrays its conductive capability with a metal like sheen.

 But workers at Berkeley Lab  found another clue to the relation
between crystal lattices and conduction, using a copper doped germanium
sliver.
 Here's a brief extract:

(Berkeley Archives URL)

<http://www.lbl.gov/Science-Articles/Archive/copper-doped-germanium.html>

Resistivity Under Pressure: Copper-Doped Germanium
September 4, 1998     By Paul Preuss, paul_preuss@lbl.gov

Germanium, doped with copper and cooled to the temperature of liquid helium,
is ordinarily a good insulator. But it becomes an astonishingly good
conductor of electricity when squeezed along one axis of its crystalline
 structure.
The surprising discovery was made by Oscar Dubon, Eugene Haller and
Wladyslaw Walukiewicz of the Material Sciences Division.

[They] found that by compressing copper-doped germanium at low temperature,
resistance dropped a trillion- fold,  permitting new studies of
semiconductor transitions.
...
"A little pressure induces a change of over a dozen orders of magnitude--
one trillion fold!--in conductivity," says Haller, pointing to a plot that
displays the resistivity of a copper-doped germanium sample abruptly dropping
 as pressure increases.
...
"You can say we have a new, smaller-gap semiconductor within the germanium
semiconductor," says Walukiewicz.
"The placement of the copper is random, but its electronic structure is
a completely delocalized extended state."
....
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brian whatcott <inet@intellisys.net>
Altus OK