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 φ 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 α-incommensurable-β phase transitions in quartz. The furnace puts no restrictions on the access of reciprocal space. It is operated under high vacuum (typically ~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.