Low Temperature Coefficient Quartz Crystals 



By W. p. MASON 



In this paper a review and amplification are given of the types 

 and characteristics of existing low temperature coefficient crystals. 

 The principal types are the coupled frequency crystals, the long bar 

 crystals, and the AT, BT, CT and DT shear vibrating crystals. 

 The theoretical frequencies for the A T and BT crystals agree well 

 with those calculated from the Christofel formula for the velocity 

 of propagation in an aeolotropic medium. For a finite plate other 

 frequencies appear which are caused by couplings to the flexure 

 and low-frequency shear modes. It is shown that harmonics of 

 the high-frequency shear mode can be excited and will have low 

 temperature coefficients. They can be made to stabilize the fre- 

 quency of ultra-short-wave oscillators. The properties of the low- 

 frequency CT and DT shear vibrating crystals are described. 

 Overtone vibrations of the shear mode of approximately twice the 

 frequency, having zero temperature coefficients, have been found 

 and these have been labeled the ET and FT cuts. 



It is shown that if two or more rotations of the cut are made 

 with respect to the crystallographic axes, a line of zero temperature 

 coefficient high-frequency crystals will be obtained. For the low- 

 frequency shear crystals a surface of zero temperature coefficient 

 crystals should result. 



In the last section the variation of frequency with temperature 

 of low coefficient crystals is discussed, and the variation of a new 

 cut, labelled the GT, is described. This cut has zero first and 

 second derivatives of the frequency by the temperature, and as a 

 result has a very constant frequency over a wide temperature 

 range. It has been applied to very constant frequency oscillators 

 and frequency standards and has given a constancy of frequency 

 considerably in excess of that obtained by other low coefficient 

 crystals. 



I. Introduction 



TOURING the past several years a number of crystal plates have 

 -*-^ been found which have the property that at a specified tempera- 

 ture their frequency will not change with a small change in temperature. 

 These crystals have proved very useful in stabilizing the frequencies 

 of oscillators used in frequency standards, broadcasting stations, radio 

 communication transmitters, airplane transmitters, and for other 

 purposes. In order to bring out their properties and spheres of 

 usefulness a review and amplification of them are given in this paper. 



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