Experimental observation of a soft mode in ammonium hydrogen oxalate hemihydrate by Brillouin scattering

1 January 1986

journal article
Published by EDP Sciences in Journal de Physique

Vol. 47 (5) , 815-819
https://doi.org/10.1051/jphys:01986004705081500

Abstract

Ammonium hydrogen oxalate hemihydrate, NH4HC2O 4,1/2 H2O exhibits a second order ferroelastic phase transition at Tc = 145.6 K. The behaviour of some elastic constants with temperature has been studied by Brillouin scattering. We observed that a xz shear deformation of the unit cell is accompanied by a softening of the C55 elastic constant. The experimental results are in good agreement with a Landau theory which takes into account the simultaneous coupling of a soft optic mode with several deformations. The role of the permanent low temperature shear deformation in the analysis of the data is emphasized

Keywords

BRILLOUIN SCATTERING

This publication has 1 reference indexed in Scilit:

Elastic properties of ammonium oxalate hydrate, ammonium hydrogen oxalate hemihydrate, and ammonium tetroxalate dihydrate
Acta Crystallographica Section A, 1972