A cryostat for collection of three-dimensional diffractometer data at liquid helium temperatures

Abstract

A beryllium-walled cryostat is described which allows collection of nearly a full sphere of accurate three-dimensional X-ray diffractometer data at liquid-nitrogen (LN2) and liquid-helium (LHe) temperatures. Cryogen consumption is 0.3-0.4 liters of LHe per hour at 30~K and 0.1-0.2 liters of LN2 per hour at 78 °K. The specimen is mounted on a copper block, the temperature of which is controlled to within 0.1 °. Measurements with a powder sample of TbVO4 show that at 33~JK the specimen temperature is within 2 ° of the temperature of the copper block. The cryostat has been used for the collection of several low-temperature data sets. Some special modifications in data-collection and dataprocessing software are described.

X-ray determination of the electron distribution in crystals of [Co(NH3)6] [Cr(CN)6] at 80 K

“…A crystal specimen (1.58 x 10 -2 mm a in volume) was sealed in a thin-walled glass capillary and mounted on a Picker FACS-1 diffractometer at Buffalo. The crystal was cooled by a conduction-type cryostat, developed by Coppens et al (1974), to 80 + 1 K with liquid nitrogen. Intensity data were collected with Mo Ka radiation.…”

The experimental charge distribution in sulfur-containing molecules. Structure determination and electron density study of NaSCN at reduced temperatures

“…A crystal, 0.25 x 0.24 x 0.27 mm, was sealed in a glass capillary and mounted in the cryostat described by Coppens, Ross, Blessing, Cooper, Larsen, Leipoldt, Rees & Leonard (1974).…”

Homogeneity of graphite-monochromated X-ray beams

“…Therefore, this problem is especially acute for the shorter X-ray wavelengths, Mo Ka and Ag Ka. When using Mo or Ag X-ray tubes some authors prefer to use fl-filters rather than a monochromator (Coppens, Ross, Blessing, Cooper, Larsen, Leipoldt & Rees, 1974). The problem of inhomogeneity is believed to be less severe or even absent for Cu Ka radiation (Birknes & Hansen, 1983).…”

“…It was shown that the distribution of intensity within the incident beam can be seriously affected when a monochromator is used (Coppens, Ross, Blessing, Cooper, Larsen, Leipoldt & Rees, 1974) and a correction procedure for the errors in single-crystal intensities due to the inhomogeneity of the incident beam has been developed and tested by Harkema, Dam, van Hummel & Reuvers (1980). The principal reason proposed to explain the inhomogeneity of the monochromated beam is the low monochromator diffraction angle.…”