Determination of the structure of the self-interstitial atom in solid argon from diffuse X-ray scattering

The diffuse X-ray intensity scattered from the displacement field of point defects in low-temperature X-irradiated argon crystals is measured. The double force tensor describing the long-range distortion field of the interstitial atom is derived from absolute intensities together with the relative lattice parameter change. The experimental results are compared with theory. This symmetry of the defect, as determined from experimental data, is in accordance with the (100) split interstitial as well as with defects with cubic symmetry, i.e. the (110) crowdion and the (110) and (111) dumb-bells can be excluded. The formation volume is found to be 0.9 atomic volumes.