Abstract
Optical anomalies near the phase transition temperature (Tc ) from the incommensurate (IC) to the α-phase were studied. In particular, large depolarization for a light propagating along the z-axis was found near Tc . The maximum of the birefringence (2·2 × 10−5) were observed in the so-called fog-zone where the ‘opalescence’appears. This and the related optical anomalies are due to the ferroelastic strains and domains induced by the modulation. However, the magnitude of the observed birefringence is by far larger than that expected from the currently accepted model unless the IC modulation wavevector k is much larger than that observed in the diffraction experiments. The results suggest the necessity of a new model for the IC phase transition in quartz.
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