A versatile high-temperature furnace for neutron four-circle diffractometers

2014 The design and performance of a versatile closed, light (0,9 kg), high temperature furnace adapted to the needs of a neutron four-circle diffractometer is reported. It operates between 330 and 1 200 K with a long term stability of better than 0.05 K. There are few restrictions on the movement of the circles; only the 03A6-range is limited to 200°. The furnace operates under high vacuum (typically ~ 10-5 mbar) with a water-cooled base. The temperature is controlled by 3 chromel-alumel thermocouples, one of which is flexible to allow it to be fixed directly at the sample. The maximum electrical power requirement is ~ 60 W. Only 2 thin-walled (0.1 mm) vanadium reflectors and an outer spherical aluminium can (cylindrical Al can in a former version) are in the neutron beam. The furnace was used successfully e.g. to collect data of the incommensurate phase at the 03B1-03B2 transition of quartz. Revue Phys. Appl. 19 (1984) 735-738 SEPTEMBRE 1984, 1. Technical specifcations. During the last few years the demand for neutron diffraction measurements at high temperatures has been increased considerably. Especially the temperature range up to about 1 200 K is of interest for experiments on e.g. structural phase transitions, ionic conductors, disorder and anharmonicity. For sufficiently precise diffraction data in most cases single crystal measurements of high quality are required. We have adopted a water-cooled vacuum furnace to the needs of a neutron four-circle diffractometer with little restrictions of the angular ranges of crystal orientation. The versatility of the device results from its low weight (0.9 kg) combined with highly flexible supply tubes for vacuum and water cooling. In this way extended data sets of reflection intensities can be collected, comparable to the situation without furnace. In the neutron beam there are only two cylindrical vanadium reflectors (0.1 mm thick each) and a thin-walled (0.5 mm) aluminium can (spherical or cylindrical). Therefore, the background is rather low and can be corrected accurately in particular by using the w-scan technique. A sectional view of the furnace is shown in figure 1 ; its characteristics are summerized in table I. The resistivity heating is realized with a thermocoaxial wire within a flexible steel tube. In this way there is no danger of a short circuit. The life time of the heater unit is not restricted by poor vacuum operation. The maximum temperature of the heater is limited to 1400-1500 K. In figure 2 there are plotted the temperatures of the two thermocouples fixed at the middle of the heater unit and at the sample position, respectively, as a function of electric power. These curves are taken at a vacuum of about 106 mbar and with clean, new V-reflectors. The temperature gradient increase with increasing temperature. It is recommended to operate the furnace only in the range up to 60 W corresponding to temperatures at the sample of about 1 200 K and at the heater of about 1 400 K. For the higher temperature region > 900 K a good reflectivity of the metal shields is essential. Nb-foils may be used instead of V to reduce the incoherent scattering background (if the much larger coherent scattering crossArticle published online by EDP Sciences and available at http://dx.doi.org/10.1051/rphysap:01984001909073500