An automatic system for X-ray studies of phase transitions at low temperatures

A low-temperature system is described for the automatic recording of lattice-parameter variations in crystals down to −185°C. The design is based on a continuous gas-flow method with `three-term' control of the local gas temperature to within ±0.5°C. The temperature can be programmed up or down over a range of 200°C. Consumption of coolant (~1 l h⁻¹) is minimized by automatically decreasing the rate of gas flow as the temperature is increased. Results obtained for the structural phase transition in Sn_0.65Ge_0.35Te are presented.