The Bell System Technical Journal 



Vol. XXII July, 1943 No. 2 



A Mineral Survey for Piezo-Electric Materials 



By W. L. BOND 



"DECAUSE of the increasing interest in piezoelectric materials in many 

 -*-' branches of science an exhaustive study of the minerals was under- 

 taken 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.* 



Considerations of symmetry show us that for a crystal to be piezo-elec- 

 trically active it must belong to a cr^^stal class that has no center of sym- 

 metry- (the Pentagonalicositetredral class of the cubic system, however, 

 although it has no center of symmetry cannot be piezo active) .^ 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 min- 

 erals classified by cr>'stal structures. As many of the non-centric ones as 

 were obtainable in the United States were tested by the method of Geibe 

 and Scheibe* (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: (*) indicat- 

 ing classes of possible activity: 



1 r>- -J 1 r Triclinic system 



2 Finacoidal j -^ 



1 Dana — A System of Mineralogy, Ford — Dana's Textbook of Mineralogy; Groth — 

 Chemische Kristalographie; Landolt Bornstein — Tabellen; International Critical Tables; 

 Zeitschrift fur Kristalographie. 



- W. Voigt, Kristal physik. 



^ Zeits f Physik 2,3, pg. 761 (1925). 



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