A new method was presented for obtaining electric twins in quartz crystals. This involved heat treatment in a temperature gradient at about 500C (below the phase transition temperature). In the case of +5X quartz crystal plates for resonators, a temperature gradient of between 15 and 25C was applied along the Y-axis length of the sample for 4 to 5h. For these resonators, the decrease in the resonant frequency and the increase in the inductance were plotted as a function of the degree of twinning.

B.Iliescu, R.Chirila: Crystal Research and Technology, 1995, 30[2], 231-5