hcp-Argoneinkristalle: Zucht und Messung der Doppelbrechung

A procedure for growing hcp argon single crystals doped with oxygen is described. The hcp crystal structure is confirmed by birefingence and neutron scattering experiments. The birefringence at 77 °K of a hcp argon single crystal doped with 2% oxygen is determined to be ne-n0 = + (2.11 ± 0.63) · 10-6. From this result one can calculate the Lorentz field factors, obtaining fo = (333 328.6 ± 1.4) · 10-6 and fe = (333 342.7 ± 2.8) · 10-8. Using Ewald's theory of structural birefringence to determine σ = c/a from the measured birefringence yields σ = (163 451 ± 3) · 10-5. This value definitely excludes the ideal hcp structure (σ = 1.63299), in contrast with the results of X-ray measurements.