Mechanical loss of calcium fluoride at cryogenic temperatures

Low mechanical loss materials are in great demand for micro-mechanical applications as well as high precision instrumentation. We describe low mechanical loss measurements of a calcium fluoride (CaF2) bulk sample. A new mechanical relaxation process was observed for frequencies in the range from 31 to 64?kHz and temperatures of 10 to 50?K. The activation energy of this process was found to be 10?meV. This relaxation process increases the mechanical loss significantly and thus sets limits to the application of this material at these temperatures.