A mini-goniometer for X-ray diffraction studies down to 4K on four-circle diffractometers equipped with two-dimensional detectors

A `universal' low-temperature device for laboratory X-ray diffractometers equipped with two-dimensional detectors has been developed. Single-crystal data collections can be performed down to 4K. Owing to its original design, the completeness of the data set is not affected by the limited number of accessible orientations of the sample. Classical structure analysis can therefore be performed as well as high-resolution (high-angle) studies for electron-density analysis. Derived from an idea of Argoud & Muller [J. Appl. Cryst. (1989), 22, 584-591], the sample is mounted on a holder magnetically coupled to the diffractometer axis. The coupling is achieved by mounting a master magnet in place of the usual goniometer head. This magnet drives a slave magnet fixed on the crystal holder: a two-axis mini-goniometer. This low-temperature arrangement is adaptable to any kappa-geometry single-crystal diffractometer equipped with a two-dimensional detector, and can be placed into various types of cryostat. This paper reports the home-made mechanical design and the performance of this device.