Optical studies of the incommensurate phase of quartz

Abstract

The results of optical studies of the equilibrium and non equilibrium properties of incommensurate phases are briefly described. Then a presentation of the results obtained on the incommensurate phase of quartz by optical measurements is given. Small anomalies of the polarization of light propagating along the Z axis have been associated with the existence of a 1q inc phase, in a small temperature interval of a few hundreths of a degree, between the β phase and the usual 3q inc phase. At the transition from the 3q inc phase to the α phase, an inhomogeneous intermediate region produces large variations of optical properties and a strong light scattering. In the inc phase birefringence measurements are very sensitive to the variations of the modulation wavevector and show clear evidence of irreversible behavior such as global hysteresis, pinning and memory effects, which are mainly related to the presence of chemical impurities. Recently a new effect has been discovered by birefringence measurements: when the rate of temperature variation is very slow, there is a crossover to a regime of discontinuous variations, which are also observed by depolarization measurements.

Key Words:

• Quartz
• birefringence
• incommensurate phase