Hybrid crystal formation in thermal transformations of potassium nitrite

Abstract
A microthermostat design for single crystal studies is described which gives control of specimen temperature in the range 30 to 100°C to an accuracy of ± 0.1 degC. For X-ray diffraction experiments the furnace comprises a beryllium tube chamber. For optical studies, the control system is combined with a chamber suitable for mounting on the stage of a polarizing microscope. Temperature cycles with single crystals of potassium nitrite indicate that the thermal transformation around 40°C from a monoclinic structure to one which is probably cubic, is continuous and reversible. Hysteresis is found in the transformation; high- and low-temperature structures co-exist in a hybrid single crystal over a temperature range.