A CLOSED-SHELL FURNACE FOR NEUTRON SINGLE-CRYSTAL DIFFRACTION

The design and performance of a versatile closed furnace adapted to the needs of a neutron four-circle diffractometer with an offset psi axis are described. It operates between 300 and 1150 K with a long-term stability of typically 0.02 K and temperature gradients across the sample of less than 0.2 K cm-1. These numbers were established by calibration 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 temperature is approximately 50 W. Four thin-walled vanadium cans and a spherical aluminium can serve as heat shields and as vacuum confinement, respectively. The furnace has been in routine operation and has been used for a series of neutron single-crystal diffraction experiments in recent years.