A Mineral Survey for Piezo-Electric Materials

A Mineral Survey for Piezo-Electric Materials By W. L. B O N D " D E C A U S E of the increasing interest in piezoelectric materials in many branches of science an exhaustive study of the minerals was undertaken with the object of finding all the materials that could possibly be of use for piezo-electric elements. Much help was derived from existing data. 1 Considerations of symmetry show us that for a crystal to be piezo-electrically active it must belong to a crystal class that has no center of symmetry (the Pentagonalicositetredral class of the cubic system, however, although it has no center of symmetry cannot be piezo active). 2 This makes twenty classes of possible piezo activity and twelve classes that could not possibly be active. About 90% of the crystals found in nature fall in those classes having centers of symmetry. Although the mineralogical data are incomplete in their assignment of minerals to definite classes in the seven systems, the existing data give a start in the choosing of minerals likely to have useful piezo-electric properties. All available data were gone through to obtain the following list of minerals classified by crystal structures. As many of the non-centric ones as were obtainable in the United States were tested by the method of Geibe and Scheibe 3 (resonance in a thermionic oscillator circuit). Whenever the authorities differed on the classification of a mineral it was so examined if obtainable. In the mineral list, each mineral is numbered according to the number of the class in Groth's Physikalische Kristallographie, as follows: (*) indicating classes of possible activity: ·JSSS^TWUc*-.