CHAPTER V 



Use of the Etch Technique for Determining Orientation 

 and Twinning in Quartz Crystals 



By G. W. WILLARD 



This paper is one of a series of papers dealing witli piezoelectric circuit elements 

 and their manufacture.^ Certain parts of the paper are not new or original, but 

 have been added for the sake of completeness and for the convenience of the 

 reader. 



5.1 Introduction 



THE manufacture of piezoelectric plates from cr>'stalline material in- 

 volves orientation problems not encountered in the fabrication of objects 

 from non-crystalline materials. The reason for this is that crystalline ma- 

 terials have physical properties which vary with the orientation, or direction, 

 in which they are measured. Since the operating characteristics (activity, fre- 

 quency, and temperature-coefficient) of the finished piezoelectric plate depend, 

 not only upon the shape and dimensions of the plate, but upon the physical 

 properties (electrical, elastic and thermal) of the crystalline material, the fin- 

 ished piezoelectric plate must have a specific orientation with respect to the 

 material as well as a specific shape and dimensions. In the case of quartz 

 piezoelectric plates the orientation problem is complicated by two factors. 

 First, a large portion of the available natural quartz cr\^stals lack such 

 natural faces as are required to determine accurately the structure-orienta- 

 tion from the shape of the original stone. Thus the raw stones must be 

 examined for structure orientation by physical instruments before even the 

 first cuts may be made. Secondly, a large portion of natural quartz cr>^stals 

 are twinned, i.e. not of the same structure orientation throughout the stone. 

 The boundaries of the respective, homogeneous regions are not predictable, 

 and cannot be completely located in the uncut stone. Thus the processing 

 of quartz involves a step by step examination for twinning boundaries and 

 orientation as the raw stone is cut into sections, the sections cut into bars or 

 slabs, and the bars or slabs cut into blanks. Even when using untwinned 

 stones the orientation must be redetermined and corrected at each cutting 

 step when making such plate types as require ver>^ exact orientation. 



The most widely used methods of determining the structure orientation 



1 See B.S.T.J., Vol. XXII: No. 2, July 1943 for Chaps. I and II; No. 3, Oct. 1943 for 

 Chaps. Ill and IV. 



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