Irrespective of the mechanism by which polarization is induced, whether spontaneously or mechanically, the induced electric field across material affects its electrical properties dramatically on the interior and the exterior regions of the material, where the built-in electric field can disrupt electronic energy states, and electric charges are rearranged.
Since the polarization of a ferroelectric changes with stress, all ferroelectric materials exhibit piezoelectricity by default. A subclass of piezoelectric materials are ferroelectric materials belonging to polar crystals, whose spontaneous polarization can be changed permanently and switched when exposed to an external strong electric field, for example, in barium titanate. A good example of such a material is zinc oxide. There are also piezoelectric materials belonging to polar crystals that exhibit a spontaneous polarization in the zero-stress state or no electric field state since there is a separation between positive and negative charges. Piezoelectric materials belonging to nonpolar crystals which are non-ferroelectric can have no electric net dipole in the zero-stress state and only generate an electric dipole under stress due to the separation of electric charge centers and a resulting induced piezoelectric potential a good example of such a material is quartz. Generally, among the 21 crystal point groups of non-centrosymmetric crystals, there are 20 point groups of crystals possessing piezoelectricity, where 10 point groups belong to nonpolar crystals which show piezoelectricity and the other 10 point groups of polar crystals exhibit piezoelectricity and ferroelectricity. When a piezoelectric material is subjected to an applied stress or mechanical vibration, the induced displacement of ions results in a net electric charge due to a change in the dipole moment of the unit cell, which builds a piezoelectric potential across the material. The origin of piezoelectricity is related to a non-centrosymmetric distribution of positive and negative electric charges in the unit cell of a material. Materials that exhibit piezoelectricity are termed piezoelectric materials, which generate an electric charge in response to applied stress (the direct piezoelectric effect), and develop a mechanical strain when subjected to an applied electric field (the converse piezoelectric effect). The term ‘piezoelectricity’ originates from ‘ piezo’ and ‘ electricity,’ where ‘ piezo’ represents the application of a pressure and ‘ electricity’ corresponds to moving electrons. Piezoelectricity was first discovered by P. Cure and J. Curie in 1880 based on their observations of the production of an electrical charge when specific materials were subjected to a mechanical force. This review provides a comprehensive overview of recent studies on how piezoelectric materials and devices have been applied to control electro-chemical processes, with an aim to inspire and direct future efforts in this emerging research field.
In addition, potential future directions and applications for the development of piezo-electro-chemical hybrid systems are described. Comparisons are made between the ranges of material morphologies employed, and typical operating conditions are discussed. The reported piezo-electro-chemical mechanisms are examined in detail. It provides an overview of the basic characteristics of piezoelectric materials and comparison of operating conditions and their overall electro-chemical performance. This review focuses on recent development of the piezo-electro-chemical coupling multiple systems based on various piezoelectric materials. There is growing interest in such coupled systems, with a corresponding growth in the number of associated publications and patents.
A more recent development is the coupling of piezoelectricity and electro-chemistry, termed piezo-electro-chemistry, whereby the piezoelectrically induced electric charge or voltage under a mechanical stress can influence electro-chemical reactions.
Piezoelectric materials have been analyzed for over 100 years, due to their ability to convert mechanical vibrations into electric charge or electric fields into a mechanical strain for sensor, energy harvesting, and actuator applications.
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