Equilibrium Vacancy Concentration Measurements on Solid Krypton

Abstract

Simultaneous length and x-ray lattice-parameter expansion measurements have been made on 6-mm-diam cylindrical specimens of 99.99%-purity krypton. The specimens were prepared and held in a rigid-tail cryostat in which specimen temperatures could be precisely controlled. The data show a divergence between the bulk and x-ray expansions at the higher temperatures, which indicates an appreciable net concentration of thermally generated vacancy defects at temperatures above 75°K. The equilibrium atomic-vacancy concentration inferred from these measurements may be represented by $\exp \left[\right({{2.0}_{-0.5\mathrm{}}}^{+1.0\mathrm{}})-(895\mathrm{}\pm 100)°\mathrm{K}/T]$. The monovacancy formation enthalpy and entropy are discussed and compared with other existing theoretical and experimental information on argon and krypton. From the present direct measurements it appears that the enthalpy of formation for the monovacancy in krypton may not be entirely accounted for by two-body central-force interactions. However, existing calculations of the contribution of many-body interactions to the binding energy of the noble-gas solids appear to be of the correct order of magnitude and sign to improve agreement between theory and experiment for the vacancy. It is found that an empirical law of corresponding states which describes a number of the bulk thermal properties of the noble-gas solids may also describe some of the defect properties.