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From what I’ve read, a piezoelectric material (like quartz) generates current from squeezing the molecule lattice and deforming it to make the positively charged atoms on one side and the negatively charged atoms on the other. If that’s all it takes to create current, couldn’t heat (which is atoms vibrating) also create current by vibrating the piezoelectric material? Especially if we made it only an atom thick so that there is high surface area to volume?

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tldr: not quite, but there are a lot of interesting applications

You're correct that a piezoelectric material interconverts mechanical energy into electrical energy. Importantly, there's both:

  • direct effect: converting mechanical deformation into electrical response
  • converse effect: converting a change in electrical field into a mechanical response

Thus a piezoelectric like quartz can generate current from vibration. This is used in quartz watches, resonators, etc. It's even used in quartz crystal microbalances - adsorbing material onto the quartz crystal will change the resonance frequency.

Importantly, the vibrations or mechanical stresses are on top of the normal vibrations of the atoms.

Moreover, if I apply a force to a piezoelectric .. say I push down on one of my group's piezo films. We do see electrical voltage or current generated through the direct effect.

From a chemistry perspective, this is an application of Le Chatelier's principle .. we have distorted a polar material, so electrical charge forms at the surfaces:

piezoelectric distortion of polar material

On the other hand, this is dynamic. When the force is removed, the current will flow back. We can measure both positive and negative current in response to a dynamic force.

In other words, if I increase the vibrations of my quartz, I'm not likely to do meaningful work.

Thermoelectrics

Some piezoelectrics are also somewhat thermoelectric. That is, they can interconvert a thermal gradient into electrical voltage.

The trick is that a good thermoelectric figure of merit requires high electrical conductivity $\sigma$ (low resistivity), among other things:

$$ z T=\frac{S^{2} \sigma}{\kappa} T $$

(S is the Seebeck coefficient and $\kappa$ is the thermal conductivity)

Conclusions and Future Work

High electrical conductivity is not conducive to a piezoelectric - if you see my diagram, the mechanical stress essentially produces a capacitor (i.e., you want to maintain that electrical field across the material.)

On the other hand, a thin piezoelectric can be good - capacitance is inversely proportional to thickness.

Single-atom thick layers can only be piezo-active in the plane, not across it. But we've made some really thin monolayer piezoelectrics:

"Intrinsically Polar Piezoelectric Self-Assembled Oligopeptide Monolayers"](https://doi.org/10.1002/adma.202007486)

As for thermoelectrics, you can find some good ones, but not quartz. You need something with reasonable electrical conductivity.

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    $\begingroup$ very recently there have been claims that energy can be harvested from the thermal motion of graphene layers. sciencealert.com/… $\endgroup$
    – UVphoton
    May 2, 2022 at 17:05
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    $\begingroup$ Yes .. it's hard to classify that as piezoelectric, since there's no polar aspect, and I'm not sure it's thermoelectric either. Some nanoscale behavior defies simple categories. But the original question isn't so far off the mark - it's possible to get some energy harvesting through nanoscale films. $\endgroup$ May 2, 2022 at 17:11

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