Anelastic Effects of Alkali Ions in Crystalline Quartz

Abstract

The anelastic behavior of natural quartz has been modified by doping with alkali ions. Three blocks cut from a single crystal of Brazilian quartz were doped with lithium, sodium, and potassium, respectively, by electrodiffusion at 500°C using a vapor-plated anode of a halide containing the desired alkali ion. Fundamental 1-Mc/sec, AT-cut shear mode resonators were fabricated from each block. Measurements of Q−1 and resonant frequency were made from liquid-helium temperatures to near the quartz inversion point at 573°C. For a resonant frequency of 5 Mc/sec internal friction peaks were evident in the low-temperature region with sodium doping giving peaks at 50° and 140°K, lithium a peak near 100°K, and potassium a peak near 200°K. The activation energies ranged from 0.06 to 0.2 eV and the relaxation times were all the order of 10−12 sec. The low-temperature behavior induced by sodium doping is of special interest since it is identical to that of certain synthetic quartz crystals. All three doped samples exhibited an exponentially increasing loss above room temperature. In each case the activation energy of the exponential loss corresponded to the activation energy for diffusion of the particular alkali ion, approximately 1 eV. Although one would infer that the loss is due only to alkali ion diffusion, it is felt that a more complex mechanism is involved at high temperatures.