Text: The history of piezoelectricity dates back to 1880 when Pierre and Jacques Curie first discovered the piezoelectric effect in various substances includin Rochelle Salt and quartz. Piezoelectric materials can generate an electric charge with the application of pressure; conversely, they can change physical dimensions with the application of an electric field (called converse piezoelectricity). In material having piezoelectric properties, ions can be moved more easily along some crystal axes than others. Pressure in certain directions results in a displacement of ions such that opposite faces of the crystal assume opposite charges. When pressure is released, the ions return to original positions. The piezoelectricity phenomena was developed and applied in sonar and quartz oscillation crystals. In 1940 the first synthetic piezoelectric substance was demonstrated. Barium titanate has piezoelectric activity nearly comparable to Rochelle salt - it is not water soluable and can withstand high operating temperatures. This ceramic material was soon followed by others, including lead metaniobate and lead titanate zirconate. In 1958, synthetic quartz material became available. If a piece of piezoelectric material is heated above a certain temperature, called a Curie temperature, it will lose piezoelectric properties. After cooling below the Curie temperature, the piezoelectric material will not regain its piezoelectric properties. Well known applications are phonograph pickups, microphones, accelerometers and roughness indicators.

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