DIRECT OBSERVATION OF FERROELASTIC PHASE-TRANSITION IN ER-DOPED LANTHANUM PENTAPHOSPHATE WITH SYNCHROTRON TOPOGRAPHY

In situ observation of the ferroelastic phase transition in Er-doped l anthanum pentaphosphate has been carried out by real time white-beam s ynchrotron radiation x-ray topography. The ferroelastic domain walls a re found to vanish and reappear with characteristics of a classical se cond-order transition on topographs on cycling the sample between room temperature and above the transition temperature. However, fluctuatio ns of the number of domain walls with temperature approaching the Curi e point are revealed for the first time and shown to be reversible. Di scussions on these interesting phenomena are presented.