A Diamond Cell for X-ray Diffraction Studies at High Pressures

A high pressure X-ray powder camera has been constructed. The instrument has been found to be useful for routine X-ray work, using molybdenum radiation, to pressures of approximately 60 kilobars. Previously reported transitions have been observed in silver iodide, potassium iodide, bismuth, and thallium. The high pressure forms and lattice parameters were found to be: AgI—f.c.c. (NaCl type), a(0)=6.067 A; KI—s.c. (CsCl type), a(0) = 4.093 A; Tl—f.c.c. (NaCl type), a(0) = 4.778 A; Bi structure not determined. These data confirm previous reports on the high pressure forms of AgI and KI. Data on Tl and Bi are apparently reported for the first time. The high pressure modifications were studied at the following approximate pressures which are not indicative of the point where the transition occurs: AgI—3.3 kilobars, KI—20 kilobars, Bi—28 kilobars, and Tl—60 kilobars. The pressure limit to which the unit can be used successfully has not been ascertained. It is believed to be much higher than the pressures reported. The present instrument is capable of producing powder diffraction patterns of materials of relatively high scattering power, giving data to 2θ=35°. High background on the X-ray powder patterns is believed to arise from scattering by the diamonds. This background may obscure weak diffraction rings. This effect may be reduced by screening, monochromatization, and other improvements in experimental technique.