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

Abstract

The origin of the light scattering observed at the alpha-beta transition of quartz is still a subject of controversy. We present structural studies performed during the coexistence of the alpha and the intermediate incommensurate (inc) phases using simultaneously synchrotron x-ray diffraction and optical techniques. The small and large angle light scatterings are due, respectively, to the orientation domains of the 3q inc phase and to the alpha phase twins revealed by diffuse x-ray scattering. In the vicinity of the interphase boundary, the two light scattering regions, both with perturbed properties, form a complex multiscale structure.

Character of the incommensurate modulation and the problem of light scattering in quartz near theα↔βtransition

“…Based on the synchrotron radiation and neutron diffraction observations by Dolino et al, 1,2 in the following we show that ͑i͒ The observed long-period IC modulation in quartz is a pure transversal acoustic ͑TA͒ modulation, without longitudinal acoustic ͑LA͒ and optic mode components. ͑ii͒ A long-period acoustic modulation cannot appear spontaneously as a result of the IC phase transition associated with the acoustic mode softening, and the mechanism of its formation should be understood.…”

“…͑ii͒ A long-period acoustic modulation cannot appear spontaneously as a result of the IC phase transition associated with the acoustic mode softening, and the mechanism of its formation should be understood. ͑iii͒ Such a modulation cannot be at the origin of any observed light scattering anomalies, contrary to the interpretation by Dolino et al 1 IC satellite reflections, in general, are contributed by the atomic displacements with respect to the crystal lattice cell ͑optical displacements͒, and by the acoustic displacements, i.e., by the displacements of a lattice cell as a whole. ͑Such a presentation should be viewed only as a simplified geometrical illustration, since the acoustic-optic mode coupling induces distortions of the lattice cells.͒ In the case of the IC structure of quartz, as shown in the present paper, one can distinguish these two contributions for some satellites, and define some important features of the IC structure.…”

“…The consideration below is mainly based on the observations of the IC satellite reflections in the elastic neutron diffraction by Dolino et al, 2 and their evolving in the synchrotron radiation diffraction. 1 As observed 2 ͑see Fig. 1͒, near the Bragg reflections of the ͑100͒, ͑200͒,¼, type, the satellites, corresponding to the IC vector k, which is parallel to the main Bragg reflection vector ͑l00͒, are systematically absent, i.e., four satellites are observed instead of six.…”

α-β Transition in Quartz: Temperature and Pressure Dependence of the Thermodynamic Quantities for β-Quartz and β-Cristobalite as Piezoelectric Materials

“…Spectroscopic techniques such as the Raman scattering [29,31,32], infrared [30], light scattering [11,27] X-ray and neutron diffraction [9,10,22,33,36,37] have been used to investigate the a and b structures in quartz.…”

Dauphiné twinning and texture memory in polycrystalline quartz. Part 3: texture memory during phase transformation

“…In situ transmission electron microscopy (TEM) showed that the phase transition is accompanied by submicroscopic Dauphiné twinning (Van Tendeloo et al 1976;Heaney and Veblen 1991a) and an incommensurate structure has been identified (Bastie et al 1988;Dolino et al 2005). Host and twin are geometrically related by a 180°rotation around the c-axis.…”