Quartz is ferrobielastic with Dauphine twins differing in the orientation of the elastic compliance and piezoelectric tensor. Therefore a suitably-oriented stress can produce different strain in the two domains, causing a free energy difference between the two domain states and producing a driving force for domain reorientation and twin wall motion.
Ferrobielastic twinning has been studied optically utilizing the photoelastic effect from room temperature up to 400°C. The coercive stress for ferrobielastic switching decrease with increasing temperature. The coercive stress needed to cause switchover in synthetic crystals is about 7 × 108 Pa at room temperature. Experiments at 150°C show switchover at 5·2 × 108 Pa and at 200°C about 1·9 × 108 Pa. The coercive stress data decrease monotonically with increasing temperature up to 250°C, above which the domain patterns depart radically from those observed at lower temperatures. The inverse relationship between coercive stress and temperature continued at higher temperature but with a discontinuity at 250°C separating two apparently linear segments.
Beyond 400°C even very small stresses are sufficient to induce twinning and it becomes difficult to observe optically, therefore the electrical method is used to study twinning at near the α-β transition. Additional details concerning high temperature twinning will be presented at the meeting.