STRUCTURAL EVOLUTION OF LIOH - EVIDENCE OF A SOLID-SOLID TRANSFORMATION TOWARD LI2O CLOSE TO THE MELTING TEMPERATURE

The structural evolution of LiOH has been studied between 10 K and 167 0 K using a combination of neutron and X-ray diffraction and calorimet ric measurements. The room temperature tetragonal phase of LiOH has be en observed down to 10 K. Above the room temperature a dehydration of solid LiOH into solid Li2O is observed at a temperature and speed whic h strongly changes with the thermal history and the partial pressure o f water vapour. Depending on these conditions the transformation of Li OH in to Li2O before the fusion temperature can be complete, partial o r suppressed. In this latter case, as previously reported in the liter ature, a first order structural phase transition of LiOH is observed c lose before the melting temperature; the transformation into Li2O is t hen observed at this temperature. (C) 1998 Published by Elsevier Scien ce Ltd.