The role of the incommensurate phase in the opalescence of quartz

Abstract

Forty five years ago, an intense light scattering was observed at the α-β transition of quartz but the origin of this opalescence has remained mysterious for a long time. Recently Saint-Grégoire et al and Aslanyan et al have explained the origin of the opalescence by introducing new incommensurate ('inc') phases with ferroelastic properties in the transition region. In this paper we recall the main features of the α-β transition, of the inc phase and of the opalescence of quartz, which presents different properties in two regions of the α-inc phase boundary. We also describe the three typical structures observed in the phase boundary regions by electron microscopy. We present briefly the two previous ferroelastic models and we propose our own explanation for the origin of the opalescence. We discuss the relations of these three models with experimental results concerning thermal behaviour, microscopic structures and the origin of the refractive index variations. Most experimental results are in agreement, at least qualitatively, with our model where the two opalescence regions correspond respectively to the presence of inc rotation patches and of irregular Dauphiné microtwins, both in a non-equilibrium state.

Optical Phenomena in the Region of Incommensurate Phases in Quartz

“…Incommensurate phases in quartz, which was revealed and studied in a number of works, for example [3,4] distinguishes obviously itself as intermediate phase in our experiment. It can be supposed also that the diffraction is a result of the incommensurate phase appearance.…”

Origin of the Opalescence at theα−βTransition of Quartz: Role of the Incommensurate Phase Studied by Synchrotron Radiation

“…The ÿ transition of quartz deserves special attention due to many important results obtained during a century of research [4]. However, the observation in 1956 of an intense transition opalescence by Yakolev et al [5] remains an unresolved question which is still a subject of controversy, recently reviewed by two of us [6]. The aim of the present work is to determine the microscopic structures at the origin of this light scattering (LS).…”

Light and X-Ray Scattering at the Incommensurate Transition of Quartz

“…These measurements were performed with the apparatus developed for the optical study of the inc phase [5]. The sample is a (10 × 10 × 10 mm 3 ) cube of synthetic quartz, with all faces polished and perpendicular to crystal axis.…”

“…In fact, as indicated in our recent review paper [5], there are two different light scattering phenomena: in addition to the large angle scattering (LAS) observed by Yakolev et al, there is, on the β phase side, a small angle scattering (SAS) of light. The two light scattering are elastic and are produced by static cylindrical objects parallel to the optical Z axis of quartz.…”

“…More recently Aslanyan et al [7] developed another ferroelastic model, but with an inc phase around b*/3 (and not close to the centre of the Brillouin zone, as observed in all previous experiments). Finally, we have recently proposed that SAS is due to a structure of equilateral triangle (EQT) and that LAS is due to Dauphiné twins, both in non equilibrium strained states [5]. The main problem is now to find the relations between the two regions of light scattering (SAS, LAS) and the three regions (EQT, ELT, Dauphiné twins) observed in various TEM experiments.…”