X-ray topographic studies of phase transition in crystals; the α-β transition of quartz

This article reviews our recent work on the α-β phase transition of quartz as a case study of phase transitions. In this work, the principal subject was to elucidate an intermediate phase (IP) which was found between α and β phases by in situ topographic observations. It turned out that IP was an incommensurate phase having a new domain structure. Also, an anomalous structure very near the transition from IP to α phase was elucidated. Since the phase transition is characterized by the structural changes on four levels of spatial scale from Å to cm, it was very necessary to use both of goniometry and topography. An emphasis is put on the methodological aspects which are useful for the study of any other phase transitions.