ISSN:
1600-5724
Quelle:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Thema:
Chemie und Pharmazie
,
Geologie und Paläontologie
,
Physik
Notizen:
The mechanism of the low = high quartz phase transformation is discussed in terms of tilting of [SiO4] tetrahedra and formation of Dauphiné twin domains below the transformation temperature. The low-quartz domain boundaries have a finite thickness. Within the domain wall the tilt angle changes gradually from + φ to -φ. Depending on temperature, the gradual change may be static or there may be a change of the average value of φ due to a dynamical process. Around the center of the wall between the low-quartz domains the structure resembles that of high quartz. The co-existence of low- and high-quartz-type regions in a temperature range below the transformation temperature is a necessary consequence of the formation of coherent domains. It is concluded that analogous ranges of coexistence of low- and high-symmetry regions exist in many, if not all, displacive phase transformations in which the phases involved have subgroup-supergroup symmetry relations and, therefore, form twin domains (dielectric, ferroelastic phase transformations, etc.).
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1107/S0567739482000540
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