Abstract
It has been proposed that single crystals of phenothiazine undergo a proper ferroelastic phase transition: Pnma()→P/c(). This premise is in conflict with Brillouin-scattering studies from both quasi- and high-symmetry longitudinal and transverse acoustic modes reported here. The elastic constant of phenothiazine as an orthorhombic crystal at ambient conditions shows no temperature dependence. The inelastic, light-scattering spectra support an order-disorder phase transition; no significantly unstable acoustic phonons were observed through the phase transition. Laser diffraction from structural domains reveals that the crystal is polysynthetically twinned above and below . At room temperature, domain walls are made indistinct by disorder but become visible as the sample is cooled. Stress-strain hysteresis below is attributed to a ferrobielastic effect.
- Received 21 April 1993
DOI:https://doi.org/10.1103/PhysRevB.48.12438
©1993 American Physical Society