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 lanthanum pentaphosphate has been carried out by real time white-beam synchrotron radiation x-ray topography. The ferroelastic domain walls are found to vanish and reappear with characteristics of a classical second-order transition on topographs on cycling the sample between room temperature and above the transition temperature. However, fluctuations of the number of domain walls with temperature approaching the Curie point are revealed for the first time and shown to be reversible. Discussions on these interesting phenomena are presented.