The thermal expansion coefficient of single crystal quartz varies with direction, as shown above*.  This makes it virtually impossible to avoid stresses due to thermal expansion coefficient differences -  e.g., at interfaces between the quartz plate and its electrodes and the mounting structure.
	Electrodeless designs, such as the “BVA” resonator, and the “all quartz package,” attempt to eliminate these stresses by mounting the quartz resonator plate on a single crystal quartz structure of the same orientation.  However, it is not the stresses but the changes in the stresses that cause instabilities, so, in other designs, compliant, spring-like mounting structures are used to minimize instabilities due to stress relief.
	*Provided by Arthur Ballato, U.S. Army CECOM, private communication, circa 1978
	R.J. Besson, “A New Electrodeless Resonator Design,” Proc. 31st Ann. Symp. On Frequency Control, pp. 147-152, 1977.
	T.E. Parker, J. Callerame and G.R. Montress, “A New All Quartz Package For SAW Devices,” Proc. 39th Ann. Symp. on Frequency Control, pp. 519-525, 1985.