Miscellaneous Piezoelectric Crystals

There are very few other piezoelectric/ferroelectric ciystals technically used in electromechanical apphcahons except quartz, tourmaline, LiNb03 and LiTa03. Other crystal materials are mostly used in special high-tempeiature applications or under development. Some of the crystals important in special applications or for the piezoelectricity or ferroelectricity studies are mentioned in this paragraph. 

Detailed hst of the material properties for the piezoelectric crystals can be foimd in I andolt-Bomstein Tables and in other sources. Also the temperature coefficients for mai of these crystals were reported. Revised and up-dated Tables of material properties for piezoelectric rrraterials were published in recent volitmes of Landolt-Bomstein Tables. Special volumes are devoted to ferroelectric and antiferroelectric substances (Group 111, Volrrmes 3, 9,16,28 and 36). 

Roehelle Salt (NaKC4H40e.4H20) crystal was the first material ever where the ferroelectricity was discovered by Valasek (1921). Crystal belong to ferro-eleetrie species 222 2, where the ferroelectric phase exists between -18 and 

24°C (erystal exhibits two Curie terrrperatures). Historically, Rochelle salt was used in apphcatiorrs for gramophone trarrsducers. Rochelle Salt has been replaced by other piezoelectric materials due to its water solubility and bad mechartical properties. 

Another possibly applicable crystal is Lithium sulfate (Li2S04.H20). It could be used below 90° C for its relatively high piezoelectric coefficients (especially for hydrostatic coefficient dh = 16.4 x 10 CN ) as a hydrostatic pressure sensor. Especially high hydrostatic piezoelectric coefficient (1000-2000 x 10 CN ) exhibits also the semiconductive ferroelectric crystal SbSI (see Fig. 7.18). Its hydrostatic piezoelectric coefficient is extremely high, but strongly temperature dependent especially at room temperature 22° C. 

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