STUDIES ON THE PHASE TRANSITIONS OF LITHIUM IODATE CRYSTALS

Abstract

The phase transitions of LiIO3 crystals have been investigated by the methods of DTA, heat-treatment at constant temperatures, and high-temperature X-ray diffraction. Our experimental results show that the τ phase of the crystal appears as an intermediate metastable phase such that a = τ→β, and it can exist only in the temperature range 230-300℃ within a period of several hours to a few days. Upon crystallization from the melt, a new phase or rather a group of new phases never mentioned previously in the literature has been revealed by X ray diffraction studies. We designate them as d-LiIO3. The difference in their structures is probably related to the cooling condition. After subsequent cooling to 200-180℃, the δ phases transform into the a phase. However, if the temperature is raised again before δ→ a takes place, then d directly transforms into β after reaching the τ→β temperature range. The results of our investigation may be summarized in the following diagram: temperature decreased immediately after endo- thermal peak appears