A gas-flow furnace for X-ray crystallography

A gas-flow furnace has been built for high-temperature single-crystal X-ray diffraction measurements using a Huber 512 four-circle goniometer. The furnace assembly is mounted on an XYZ stage which is fixed to the φ-axis counterbearing and the sample is mounted on the φ circle. The XYZ stage allows a determination of the temperature profile around the sample and a selection of the optimum furnace position. The sample temperature is measured with a thermocouple placed 0.5 mm from the center of the crystal. Thermocouple temperature was calibrated up to 991 K using the thermal expansion of a single-crystal of NaCl. The accuracy of the sample temperature measurements and the fluctuations of the sample temperature are both better than ± 2 K. The furnace has been successfully used to study the crystal structures and the thermal expansion of β-Mg₂SiO₄ up to 1100 K and the phase transitions in ilvaite, Ca(Fe²⁺ Fe³⁺) Fe²⁺Si₂O₇O(OH), and anorthite, CaAl₂Si₂O₈, at 346 and 516 K, respectively.