X-Ray Diffraction of Substances under High Pressures

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Abstract
An apparatus is described which may be used for x-ray diffraction work on substances under pressures up to 5000 atmospheres. The compressive medium is helium gas. A small (2.5 cm radius) Debye-Scherrer type camera is used. The camera, complete with film and specimen, was placed inside the high pressure chamber. The x-rays make their entrance through a beryllium window in the chamber wall. A general blackening of the film by scattering from helium is prevented by slits installed for this purpose, and the quality of the x-ray diffraction lines is quite good. Results are given for the transition AgI (II) to AgI (III). The crystal structure of AgI (II) is found to be cubic (NaCl type). The volume change in this transition is found to be greater when measured by x-ray methods than when measured by over-all methods. An interpretation of this is given. Some results on cadmium and RbCl are also described.

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