Dielectric and Optical Properties of Crystalline Argon

Abstract

Studies of the crystal optics, dielectric properties from 10 Hz to 10 kHz, and the electro-optical properties of crystalline argon, grown with a modified Bridgman technique, are reported. The optical character of the solids was examined using polarized light, with varying crystal growth parameters, viz., rate, annealing, and pressure. Using crossed polaroids to examine the transparent crystals, three basic kinds of optical regions were observed: optically isotropic, optically anisotropic (birefringent), and sharp, horizontal, alternate isotropic and anisotropic striations. Low-order strain birefringence with broad and diffuse patterns is also described. The observations are considered in terms of impurity segregation and strain effects and it is concluded, with support from annealing and electro-optic studies up to 40 kV/cm, that the birefringent regions have hcp structure and the isotropic regions have fcc structure. The dielectric constant (ε) was directly measured for solid argon between two concentric stainless-steel cylinders in a three-terminal network that minimized stray fields. It was found that ε = 1.586 over the entire frequency range with an estimated experimental error of 2%. Variation of ε with growth rate and annealing qualitatively supports the optical observations on hcp and fcc structure.