A question which just occurred to me. For other physical properties, there are cases where an alloy has different or better properties than a pure element. For strength, steel is an obvious one, beryllium copper maybe another. And combinations sometimes have surprisingly different behaviors: for example, some ratios of sodium and potassium are actually liquid at room temperature.
So it doesn’t seem ‘a priori’ impossible, though I don’t know of any such materials. On the other hand, maybe there is some fundemental physics which renders this unlikely?
Here’s an engineering table that lists the resistivity of elemental metals and some common engineering alloys.
There are no novel and exotic alloys in that list (assuming such things exist), but all the alloys in the second table are significantly more resistive than pure silver or copper.
I also saw in my googling an assertion that any alloy will have resistivity greater than any of its component metals, but no proof of that assertion.
‘>>> I also saw in my googling an assertion that any alloy will have resistivity greater than any of its component metals, but no proof of that assertion.’
Right, this seems to be a sort of article of faith. And it may well be true, though I would like to know if there is any theoretical basis for it.
Just wondering if this ‘common knowledge’ might have inhibited research into possible new materials. After all, the cuprate superconductors seem to have come out of left field by serendipity? Not that they have really been game changers, so far at least…
And not to be pedantic, but a “better electrical conductor” doesn’t necessarily mean it has higher conductivity vs. another conductor; it could have lower conductivity, but be “better” in a different way for a certain application. As an example, for overhead power lines, copper would not be a better conductor than aluminum, even though copper is more conductive than aluminum.
I’m not certain that this is correct, but I’m certain it will have resistivity greater than its most conductive component metals. The curves are convex downward and sloped between the two endpoints, for two component alloys, and are similar surfaces for three component alloys. It’d be a question whether the curvature is ever less important than the slope at the lower end or point.
This is also the case for thermal conductivity, which for metals tracks quite well with electrical conductivity. In metals it’s the outer electrons that contribute most to both.
A moment’s thought would show that that can’t be completely true. That would mean that, for instance, silver with any lead impurity in it at all, no matter how trace, would have a higher resistivity than lead. And of course, one never encounters any completely-pure element.
Now, a resistivity greater than its least-resistive component, that I could believe.
I would guess that the core of the idea is that alloying brings with it more lattice dislocations which bring with them more scattering sites and generally get in the way.
There can be a difference in resistivity simply by transitioning from the austenite to martensite phases in some metal alloys. So just juggling the atoms about.
Of course superconductors are not pure metals. So the idea only has so much traction. But the conductivity is fundamentally different in superconductors.
Maybe there are some magical alloys that promote really regular lattices and suppress defects. Maybe some are actually better conductors. Seems doubtful. Problem is that most alloys are actually a matrix of crystals, each a pure metal. To create something magical one may need an intermetalic compound. That is where many superconductors come in. So maybe. But I wouldn’t hold my breath.
Francis: " most alloys are actually a matrix of crystals, each a pure metal. To create something magical one may need an intermetalic compound"
That’s an interesting question. Why in fact do alloys mostly form as crystals like that, rather than being more mixed at the atomic level? Do we have a good theoretical understanding of this?
Aluminum wire that’s used for electrical power (e.g. AA-8000 series) is not pure aluminum. It is aluminum plus small quantities of zinc, titanium, manganese, and silicon.
One thought is whether we would find something in new nanostructures rather than traditional alloys. Stacked graphene or other 2D crystals, arrayed nanowires, etc. could introduce ballistic transport, which might display significantly higher conductivity than simple elements or alloys.
Of course, making exotic nanostructures in the volume and length to be useful is a separate topic…
In general, the worse the conductivity, the higher temperature the superconductor. All of the highest Tc metallic superconductors are alloys (or compounds). And of course, the rare earth superconductors are actually ceramics.
This is what I’ve read regarding thermal conductivity. IIRC, electrical conductivity too – and since the two track so well in the case of metals this is what we’d expect.
Yes, it’s different rules in the case of superconductors, as the electrons travel “ballistically” (I think I’ve read).
No, superconductivity doesn’t involve ballistic transport of electrons. The charge carriers are electron pairs and the pairs can’t (because of the energy required) give up momentum to the lattice (i.e. resistive flow).
Well, a theorist would probably complain that my simplistic explanation is wrong as well, so don’t feel bad. Superconductivity is a very exotic quantum mechanical property of solids. They don’t really have a solid explanation of all the mechanisms behind all of the newer superconductors. (at least not an explanation that all the theorists agree on).
Now here’s an interesting experiment. I posed this question to ChatGPT, and it responded as below.
So, is anything it says correct?
ChatGPT:>>> Yes, there are several silver alloys that have better electrical conductivity than pure silver.
One example is silver-copper (Ag-Cu) alloy, which is commonly used in electrical applications such as wires, cables, and connectors. This alloy has a higher conductivity than pure silver, as the addition of copper helps to reduce the electrical resistance of the material.
Another example is silver-palladium (Ag-Pd) alloy, which is used in high-performance electrical contacts and switches. This alloy has a higher conductivity than pure silver and is also more resistant to wear and corrosion. <<<
Right. So where is ChatGPT getting its “information” from? I’m starting to get concerned that we will soon be inundated with so-called ‘knowledge’ that is really just distilled folklore. Been that way since the start of the Internet, I guess, but this makes it worse.
Off topic, I know. Maybe time for a different discussion?