[jcims]

Every time some phenomenon arises from a recipe of fairly typical materials I wonder what other surprises nature has in store for us.

The idea that the crystalline structure plays a large role in the bulk thermal conductivity of the material is kind of mind-blowing at first and then retrospectively obvious.

[adw]

I am twenty years removed from it, but I used to be well-informed on this kind of thing; I have a PhD in mineral physics.

Let's see how well I can explain this (haven't read the article, yet, sorry! Waiting for a plane...)

So you're no doubt familiar with the physics of a vibrating string; it resonates at wavelengths (length of string, 2 * length of string, 3 * length of string... n as n->inf). So you can express any vibrational state of the string as sum(intensity * wavelength); so you can represent the state of the string as a vector of intensities on a basis of allowable vibrations of the string.

Let's call these _vibrational modes_. Let's assume occupancy of these modes is quantized. It's (sort of...) the same as energy levels of atomic orbitals in electronic structure, if you remember that from chemistry classes; the way it's not the same is important (bosons vs fermions) but not at this level of handwaving :-)

So this is how solids store energy, and we call this energy "heat".

A reasonable approximation for a crystalline structure is balls – point masses – connected by springs, where the springs are covalent bonds, plus electrostatic effects between point charges. Intuitively, you can follow that the same kind of _vibrational spectrum_ will arise from this arrangement (in the same kind of way; the solutions of the differential equation of this system of forces under periodic boundary conditions). So materials have resonant frequencies in the same way guitar strings do.

Therefore, this vibrational spectrum defines the thermal behavior of a material; heat capacity, thermal conductance, etc etc etc etc. Each of these vibrational modes is also tied to a collective motion of the particles in the material, which (if sufficiently violent) will tear the structure apart – there's the solid-to-liquid phase transition – or, more subtly, if lost will lower the symmetry of the crystal structure, which gives rise to solid-to-solid phase transitions (an example would be alpha to beta quartz, which will crack your crockery if you leave it in the oven on a cleaning cycle; https://en.wikipedia.org/wiki/Quartz_inversion).

There's a lot of depth here, as you can imagine!

[correct_horse]

I think you meant to say length of string, length of string / 2, length of string / 3, ...

https://en.wikipedia.org/wiki/Harmonic

[adw]

Indeed I did! Thank you. (This is what happens when you write in a hurry.)

[mkagenius]

Hope you had a nice flight. Happy new year.

[adw]

One leg down, the long one to go...

[7373737373]

This reminds me of this Sixty Symbols video which explains why light is slower in media such as glass than in a vacuum:

https://www.youtube.com/watch?v=CiHN0ZWE5bk

The incoming light wave causes an avalanche of secondary waves through electromagnetically perturbing the individual atoms, and the superposition of all these results in a wave that seems to travel slower than the speed of light.

[diegoperini]

> A reasonable approximation for a crystalline structure is balls – point masses – connected by springs, where the springs are covalent bonds, plus electrostatic effects between point charges.

Thanks! This is a great analogy.

[infinite8s]

This is the model used by most chemical simulation codes (that don't account for quantum chemistry). See for example the LAMMPS simulation software (https://lammps.sandia.gov/)

[adw]

If anything I wrote has been original, it would have been a big red flag :-)

[jcims]

This is so cool, thank you. I dabble informally and quite primitively with signal processing, so the idea of vibrational spectrums in a crystalline structure really resonates (hurrr). Now i have a whole new set of mental imagery to process when i pick up the pan with a handle that had the handle a little too close to the flame. Thanks!!

[stjohnswarts]

I hate to mess with your physics education but silicone covers for all your metal pan handles is a godsend, even for atheists.

[peter_d_sherman]

Great information!

Also, (and I may be totally wrong about this!), the concept of Annealing from metallurgy -- seems related to that of Quartz Inversion:

https://en.wikipedia.org/wiki/Annealing_(metallurgy)

[kragen]

Well, both annealing and dunting ("quartz inversion") have to do with the crystalline structure of materials, but that's where the similarity ends. There are many important crystalline phase transitions in metallurgy that are more similar to dunting; the most important of many examples is probably the ferrite-to-austenite transition in steels at 700–1400°. But annealing is not such a crystalline phase transition.

[agumonkey]

Well written I must say. Makes me very curious about crystals and material physics (especially since I got interested in low level electronics and semi conductors).

Any suggestion to read ?

[adw]

Not really light reading, but any good solid-state physics textbook would cover most of this. I learned from https://www.amazon.co.uk/Introduction-Mineral-Sciences-Andre..., which is quite a bit more explicitly mineral-sciences focussed.

[agumonkey]

Aight, I'll see if I can digest it.

[abdullahkhalids]

The space of "fairly typical materials" is very wide because there are lots of elements and their combinations blow up very fast. Secondly, materials are often very sensitive to small physical or chemical changes, resulting in wildly differing properties.

To you the simpleness of the final result is surprising, but that simple result was discovered after a long and exhaustive search. A search into a wide and shallow space can be just as impressive and difficult as a search into a narrow and deep space.

[darkteflon]

I think OP was just expressing delight and wonder at our surprising and elegant universe rather than making light of the findings.

[ragerino]

Actually looking into independent power sources for small IoT sensor stations for a hobby project. I think to understand climate change better, we need more data.

Engineer here btw.

[jcims]

Yep! Delight is a great word for it.

[jcims]

It goes even beyond the combinations, no? The physical manifestation of the end material plays a key role in its properties, so you could just make a simple alloy of the above and not have this thermoelectric effect. Only when you apply them just so do you get this outcome. So crazy...

[JumpCrisscross]

> a recipe of fairly typical materials

We don’t have good theory for materials science. Our understanding is closer to a list of observations (“effects”) than anything unifying. That almost ensures there will be surprises in the gaps.

At the same time, popular disillusionment with repeated claims of wonder materials has led to—in my opinion—underinvestment in basic research.