A CLOSED-SHELL FURNACE FOR NEUTRON SINGLE-CRYSTAL DIFFRACTION

The design and performance of a versatile closed furnace adapted to th e needs of a neutron four-circle diffractometer with an offset psi axi s are described. It operates between 300 and 1150 K with a long-term s tability of typically 0.02 K and temperature gradients across the samp le of less than 0.2 K cm-1. These numbers were established by calibrat ion work at the alpha-incommensurable-beta phase transitions in quartz . The furnace puts no restrictions on the access of reciprocal space. It is operated under high vacuum (typically approximately 10(-3) Pa), with a water-cooled base. A flexible mantled thermocouple may be fixed directly on the sample. The maximum power needed at the highest tempe rature is approximately 50 W. Four thin-walled vanadium cans and a sph erical aluminium can serve as heat shields and as vacuum confinement, respectively. The furnace has been in routine operation and has been u sed for a series of neutron single-crystal diffraction experiments in recent years.