Some experimental results on quartz-crystal resonators at temperature below 4.2 K

Properties of quartz-crystal resonators at temperature below 4.2K have been measured for two different types of crystals: 5-MHz resonators of the BVA₂ design (electrodeless design) and the conventional 5th overtone, AT-cut design. The Q for both types is increased by about one order of magnitude at 4.2K. No significant increase in Q below 4.2K was obtained in either type of resonators. The temperature coefficient near 2K is greatly reduced compared with the value at 4.2K for one sample of each type. The BVA₂ sample shows the temperature coefficient of 3×10^-10/K at 2K. The frequency variation versus dissipated power in crystals is very steep above 10^-7 W below 4.2K.