Theoretical solid state chemistry Piezoelectric effect

The total energy imparted to the piezoelectric element by an external mechanical force is equal to the sum of the elastic deformation energy and the charge energy of the capacitance of the piezoelectric element. Due to the reversibility of the piezoelectric effect, a piezoelectric reaction occurs: the electrical voltage arising from the direct piezoelectric effect creates (as a result of the inverse piezoelectric effect) mechanical stresses and deformations that oppose external forces. This is manifested in an increase in the rigidity of the piezoelectric element. If the electric voltage arising from the piezoelectric effect is eliminated, for example, by short-circuiting the electrodes of the piezoelectric element, then the reverse piezoelectric action will not be observed and the rigidity of the piezoelectric element will decrease.

@benzol00 Thank you, I would like to understand the essence of the electric voltage in the piezoelectric effect, what is it caused by, where does the electric current and electrons come from?

@nanochimik47 Consider the example of silicon. In the crystal structure, each silicon ion Si, which has a positive charge of + 4e, is tetrahedrally encompassed by four ions and alternates with negative oxygen ions -2e, and each of the oxygen ions is simultaneously bonded to two silicon ions, and one silicon ion requires two oxygen ions according to the formula SiO2. However, the charges of all ions of the crystal cell cancel each other out, and it is electrically neutral. If we observe each pair of oxygen ions as a particle with a charge of -4e, then the structural cell shown in (picture 1a) will take the form shown in (picture 1b). Suppose that an external force acts on this cell in the direction of the electric axis X (picture 1c), then the Si-1 ion will shift and find itself between the O-2 and O-6 ions, and the O-4 ion is in the middle of the Si-3 ions and Si-5. Therefore, a positive charge will appear on one surface, and a negative charge on the other, which means there will be a direct piezoelectric effect.

@benzol00 Thank you very much for the illustration, the electrons coming out are taken from the O atoms?

@argentum Yes, sure 😀