The pyroelectric effect, by which a material…

The pyroelectric effect, by which a material generates an electric potential in response to a temperature change, had been studied by Carl Linnaeus and Franz Aepinus in the mid-eighteenth century.

Drawing on this knowledge, both René Just Haüy and Antoine César Becquerel had posited a relationship between mechanical stress and electric charge; however, experiments by both had proved inconclusive.

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

Quartz and Rochelle salt exhibit the most piezoelectricity, which describes the charge that accumulates in certain solid materials (notably crystals, certain ceramics, and biological matter such as bone, DNA and various proteins) in response to applied mechanical stress.

The Curies, however, had not predicted the converse piezoelectric effect, which is mathematically deduced from fundamental thermodynamic principles by Gabriel Lippmann in 1881.

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

Piezoelectricity will remain something of a laboratory curiosity for the next few decades.