Discontinuous variations in the incommensurate phase of quartz: Synchrotron-radiation observations of a mechanism for temperature variation of the modulation wave vector

High-resolution diffraction experiments using white-beam synchrotron radiation have shown that discontinuous variations of the modulation wave vector q are observed in the incommensurate phase of quartz for a slow rate of temperature variation. Spatial discontinuities of q are also observed under a stable temperature gradient. These observations are discussed in relation with various models, and a mechanism for the temperature variation of q is suggested.