Low temperature coefficient quartz crystals

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 frequency 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.