Structural relaxation in silicon at low temperatures

The lattice spacing of a perfect crystal of silicon has been measured by means of X-ray diffraction according to the Bond method coupled with a quadruple-crystal monochromator; measurements were repeated over several thermal cycles in a range from room temperature to 20 K, on cooling and heating, It is found that the lattice spacing depends on thermal treatments of the specimen, in particular those at low temperatures. and that anomalies around 50 K become significant after the thermal cycles. The results suggest the existence of a slow relaxation process for rearranging defects and host atoms in the silicon lattice.