The Signal Corps Synthetic Quartz Program

The role of the Signal Corps in developing the various techniques now being used to synthesize quartz crystals is reviewed from the standpoint of the quality of the material produced, growth rate, growth conditions, seed orientation, feed materials, cost, and suitability for production. Differences in the structure of synthetic quartz are indicated by variations in the optical absorption coefficients of X-irradiated quartz plates taken from different growth directions. The optical absorption measurements on the different types of synthetic quartz are compared with one another. Differences in the structure of natural and synthetic quartz are also indicated from measurements of Q made on 5-Mc high-precision resonators fabricated from samples of synthetic quartz grown under different conditions and from the occurrence of large absorption peaks at low temperatures (50°K) noted when measuring such resonators. Data is presented to show that synthetic quartz grown in the Z-direction possesses higher Q´s than other quartz growth directions. None of the 5-Mc units made from synthetic quartz approach the high Q typical of natural quartz 5-Mc units between ¿60°C and 100°C. Comparison of the frequency temperature characteristics of overtone high frequency resonators made from synthetic quartz with those made from natural quartz show them to be about the same. The growth direction and impurity content, however, change the optimum orientation angle and inflection temperature. Resonators processed from synthetic quartz for operation in the 60-202-Mc range are shown to perform as satisfactorily as similar resonators made from natural quartz.