Updated: Oct 11, 2020
How dipoles in nonpoint symmetrical compounds generate electricity and shape the world
The piezoelectric effect is a phenomenon by which certain materials can generate current in response to mechanical stress. Similarly, the inverse piezoelectric effect describes how these materials experience mechanical deformation in response to an electric current running through them. It was postulated and then discovered in 1880 in Paris, France by Paul-Jacques and Pierre Curie in an experiment where a crystal in between two tin sheets was compressed. An electrometer then detected electrical charges on the faces of the crystal, which drove an electric current throughout a circuit. Furthermore, they found the magnitude of the charges to be directly proportional to the force of compression (Curie & Curie, 1880).
Piezoelectricity arises from the molecular structure of certain materials. These materials are often crystalline, but what’s important is that they lack a point of symmetry and have unequal charge distributions between their atoms. Take quartz, for example, a mineral composed of SiO4. Its tetrahedral structure with a silicon atom in the center means that it has no point of symmetry. Furthermore, silicon and oxygen have significantly different electronegativities, so silicon will have a slightly positive charge, and the oxygen atoms will have a slightly negative charge. Typically, the dipole moment vectors between one of the oxygens and the silicon atom all cancel out; However, compressing the molecule alters the direction of the vectors such that there is a net positive charge on one side and a negative charge on the other. The resulting difference in electric potential occurs throughout the crystal, allowing the quartz to drive a current.
A wide variety of materials are piezoelectric. Because of the phosphate groups in nucleic acids, DNA is piezoelectric. Other piezoelectric materials include sugar, topaz, tourmaline, silk, and bone. One of the first applications of piezoelectricity was in sonar instruments, which ran current through crystals, causing them to vibrate and generate soundwaves. Many electronics and appliances like electric toothbrushes, clap-on lights, microphones, electric instruments, and Inkjet Printers. Research has also shown promising biomedical applications in new fertility treatments, prosthetic limbs and imaging techniques (Nakayama et al., 1998; Zhou et al., 2014)
Curie Jacques, Curie Pierre. Développement par compression de l'électricité polaire dans les cristaux hémièdres à faces inclinées. [Development, via compression, of electric polarization in hemihedral crystals with inclined faces] In: Bulletin de la Société minéralogique de France, volume 3, 4, 1880. pp. 90-93.
Nakayama, T. (1998). A New Assisted Hatching Technique Using a Piezo-Micromanipulator. Fertility and Sterility, 69(4), 784-788. doi:10.1016/s0015-0282(98)00017-x
Zhou, Q., Lam, K. H., Zheng, H., Qiu, W., & Shung, K. K. (2014). Piezoelectric single crystal ultrasonic transducers for biomedical applications. Progress in Materials Science, 66, 87-111. doi:10.1016/j.pmatsci.2014.06.001