Ferroelectrics Turn 100!

This year we commemorate the first report of ferroelectricity a century ago, but the full story goes much further back. In the 17th century there stood an apothecary shop in La Rochelle, a seaport in western France. The shop was run by Jehan Seignette (1592–1648),who had two sons: Pierre (1623–1719) and Élie (1632–1698). Pierre became a medical doctor at the University of Montpellier while his brother Élie eventually took over the pharmacy. In those days pharmacy consisted mainly of plant extractions and distilled essences.Laxatives like senna leaves played an important role, but because of unpleasant side effects patients were reluctant to take them. For this reason, Pierre suggested to his brother that he might instead find some mineral drugs, as were used in the East for millennia. In around 1665–1672  Élie  probably  reacted  potassium  hydrogen  tartrate (KC4H5O6), a natural byproduct of winemaking (Le Rochelle is just 184km from Bordeaux) also known as potassium bitrate or cream of tartar,with sodium bicarbonate (baking soda, NaHCO3), which makes the tartrate soluble in water. He thus succeeded in producing a salt which he called“sel polychreste,”a combination of the French“sel” (salt) and Greek“πoλυχρηστoσ”(multi-purpose); but it was also often referred to as “Seignette salt.”He produced the salt in large quantities with his brother,  but  his  synthesis  method  and  even  the  composition (KNaC4H4O6•4H2O) remained a family secret for some 65 years–outliving both brothers. It was eventually French pharmacist and chemist Simon Boulduc in Paris who found by analysis that“sel polychreste”must be“some soda”[1]. It took nearly two centuries for work to continue on the salt. In 1824 David Brewster observed several crystals, including Rochelle salt, in which the degree of polarization was a function of temperature. He named this effect pyroelectricity[2].In fact, this phenomenon had already been described by the Greek philosopher Theophrastus (c. 314 BC) in reference to the ability of tourmaline to attract straw or sawdust when heated. In 1880 Pierre and Paul-Jacques Curie found that pressure applied to certain crystals, including Rochelle salt, resulted in polarization which was proportion alto the applied strain and which reversed as the polarity of the applied field was reversed. This effect was termed piezoelectricity. In 1899 Thomas Edison was perhaps the first to use the piezoelectric response of Rochelle salt in a commercial application–the phonograph; however,the expense of this invention made it just a curiosity at the time.