Zero Temperature Coefficient Quartz Crystals for Very High Temperatures

Most quartz crystals used to control the frequency of oscillators or time measuring devices are used in places where the ambient temperature does not exceed 60° to 70°C. The crystals are usually adjusted in angle so that they have a zero temperature coefficient at a temperature of about 80°C and they are temperature controlled at this temperature. However, a class of uses occurs for which the ambient temperature may be considerably higher and for these uses ordinary AT and BT crystals, for example, are not satisfactory. This is evident from Figs. 1 and 2 which show the frequency variations for these crystals over a temperature range from -- 100°C to +200°C. For example, the flattest frequency temperature curve for the AT cut occurs at an angle of + 3 5 ° 18' rotation about the X axis from the Y cut. By going to +35°36' orientation about the X axis a minimum occurs at 100°C. For the BT cut shown by Fig. 2 the angle of - 4 9 ° 1 6 ' orientation gives nearly a parabolic shape centered at 20°C. By changing the orientation to -- 47°22' the parabola centers at 75°C. Hence if one wishes to raise the temperature for which the zero temperature coefficient occurs he has to increase the rotation about X for the AT cut and decrease it for the BT cut. The amount needed for either orientation can best be determined by evaluating the elastic constants as a function of orientation and temperature, and that is the main purpose of this paper. The results are applied to determining the best angles of orientation for the AT, BT, CT, and DT type crystals to obtain zero temperature coeffi366