Man-made quartz crystal

Quartz, although a common mineral, occurs relatively rarely in crystal form and of size and quality suitable for resonator manufacture. Synthetic quartz had been produced by a number of experimenters for over 100 years by various methods. The shortage of natural electronic-grade quartz and the voracious and ever increasing demand, aroused a new and immediate interest in its synthetic production. Reference is made to the experimental work carried out by Spezia who conceived the idea of using small pieces of natural quartz on which to grow, by deposition, synthetic quartz. His early work formed the foundation for the later development of successful industrial processes. Serious work on the growth and properties of synthetic quartz dates from about 1946. Spezia's temperature-gradient technique with quartz nutrient, but with changes in the conditions he had employed with respect to pressure, temperature and the nature of the starting solutions, was adopted. The paper describes a project initiated in 1958 and the production plant which was employed. The process consisted basically of a single autoclave having a lower zone at elevated temperature in which a nutrient material dissolves and an upper growth zone at a lower temperature in which crystallisation occurs. A detailed description is given of the production process. The properties of quartz in relation to its use for resonators are evaluated and a comparison is drawn between those of natural quartz and those of synthetic. As the growth rates of synthetic quartz are increased the properties approach more nearly those of natural quartz. Economies however dictates whether complete equivalence is essential in particular applications. As growth techniques are improved it is expected that production costs will fall. New doping techniques have already been successfully used to improve certain specific crystal properties.