Brillouin-scattering study of the elastic constants of phenothiazine through the phase transition

Authors

J. Sartwell, University of Nebraska - Lincoln
Craig J. Eckhardt, University of Nebraska - LincolnFollow

Date of this Version

November 1993

Comments

Published by American Physical Society. Phys. Rev. B 48, 12438 - 12448 (1993). http://link.aps.org/abstract/PRB/v48/p12438. Copyright © 1993 American Physical Society. Permission to use.

Abstract

It has been proposed that single crystals of phenothiazine undergo a proper ferroelastic phase transition: Pnma(D_2h)→P2₁/c (C_2h). This premise is in conflict with Brillouin-scattering studies from both quasi- and high-symmetry longitudinal and transverse acoustic modes reported here. The C₅₅ 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 T_c. At room temperature, domain walls are made indistinct by disorder but become visible as the sample is cooled. Stress-strain hysteresis below T_c is attributed to a ferrobielastic effect.