Piezoelectric Molecular Crystal: The word piezoelectricity means electricity resulting from pressure and latent heat. It is derived from the Greek word piezein, which means to squeeze or press, and, ēlektron which means amber, an ancient source of electric charge.

New Delhi (ABC Live India): A group of researchers from the Indian Institute of Science Education and Research  Kolkata, the Indian Institute of Technology Kharagpur and RWTH Aachen University, has found a type of piezoelectric molecular crystal that is capable of autonomous self-healing.

The paper was published in the journal Science, explains the research work on piezoelectric molecular crystals and the crystals grew that could heal themselves.

As the researchers note, self-healing materials have become the object of intense research in recent years. Such efforts have yielded some results polymers, gels, and other materials have been developed which, when injured, can heal themselves to some degree. To date, such successes have all had one thing in common—they are all soft. In this new effort, the researchers tackled a much more difficult task: finding or developing a self-healing hard material. In this case, that meant figuring out how to get a dense material, made of molecules arranged in a regular way, to heal when ripped apart.

The published research reasoned that the inherent properties of such crystals should lend themselves to self-healing because of their attractive forces. After intensive trials, it was decided to use bipyrazole organic crystals for their research, and thereafter the team grew a sample of crystals in tiny (2mm long by 0.2mm wide) needle shapes.

Then the Researchers applied pressure on crystals to make them break, and found that after the break, the needle regained its original shape, meaning thereby that crystals material has piezoelectric property.

Know About the Piezoelectricity

Piezoelectricity is the electric charge that accumulates in certain solid materials (such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins) in response to applied mechanical stress.

The word piezoelectricity means electricity resulting from pressure and latent heat. It is derived from the Greek word piezein, which means to squeeze or press, and, ēlektron which means amber, an ancient source of electric charge.

History of Piezoelectricity

The Wikipedia on the History of Piezoelectricity writes  that the pyroelectric effect, by which a material generates an electric potential in response to a temperature change, was studied by Carl Linnaeus and Franz Aepinus in the mid-18th century. Drawing on this knowledge, both René Just Haüy and Antoine César Becquerel posited a relationship between mechanical stress and electric charge; however, experiments by both proved inconclusive.

The first demonstration of the direct piezoelectric effect was in 1880 by the brothers Pierre Curie and Jacques Curie. They combined their knowledge of pyroelectricity with their understanding of the underlying crystal structures that gave rise to pyroelectricity to predict crystal behavior, and demonstrated the effect using crystals of tourmaline, quartz, topaz, cane sugar, and Rochelle salt (sodium potassium tartrate tetrahydrate). Quartz and Rochelle salt exhibited the most piezoelectricity.

A piezoelectric disk generates a voltage when deformed (change in shape is greatly exaggerated).

The Curies, however, did not predict the converse piezoelectric effect. The converse effect was mathematically deduced from fundamental thermodynamic principles by Gabriel Lippmann in 1881.

The Curies immediately confirmed the existence of the converse effect, and went on to obtain quantitative proof of the complete reversibility of electro-elasto-mechanical deformations in piezoelectric crystals.

For the next few decades, piezoelectricity remained something of a laboratory curiosity, though it was a vital tool in the discovery of polonium and radium by Pierre and Marie Curie in 1898. More work was done to explore and define the crystal structures that exhibited piezoelectricity.

This culminated in 1910 with the publication of Woldemar Voigt's Lehrbuch der Kristallphysik (Textbook on Crystal Physics), which described the 20 natural crystal classes capable of piezoelectricity, and rigorously defined the piezoelectric constants using tensor analysis.

Application of piezoelectric Materials

Currently, industrial and manufacturing is the largest application market for piezoelectric devices, followed by the automotive industry. Strong demand also comes from medical instruments as well as information and telecommunications. The global demand for piezoelectric devices was valued at approximately US$21.6 billion in 2015. The largest material group for piezoelectric devices is piezoceramics, and piezopolymer is experiencing the fastest growth due to its low weight and small size.