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Article Dans Une Revue Journal de Physique Année : 1989

Phase transitions in C2O4H NH4 1/2 H2O : a light scattering study of the high pressure phase

Résumé

AHO exhibits, at normal pressure, a ferroelastic, second order phase transition at 145 K (160 K for AHOD). A new phase (phase III) has been identified under pressure, by its characteristic Raman features. One specific aspect is the existence of two low energy modes, the frequency of which is highly pressure dependent. Phase III has been shown in [6] to be incommensurate with a wave vector q0//c*, q0 strongly varying with pressure. These low frequency modes are acoustic phonons belonging to two branches activated by the incommensurability, and we propose that phase III would be, as phase II, produced by the ordering of ammonium ions linearly coupled to the third acoustic branch, this coupling taking place at q0 for phase III and at the zone center for phase II. This mechanism explains the behaviour of a central peak detected in the B2g geometry.

Dates et versions

hal-04084556 , version 1 (28-04-2023)

Identifiants

Citer

Jean-Luc Godet, M. Krauzman, R.M. Pick, H. Poulet, N. Toupry. Phase transitions in C2O4H NH4 1/2 H2O : a light scattering study of the high pressure phase. Journal de Physique, 1989, 50 (13), pp.1711-1728. ⟨10.1051/jphys:0198900500130171100⟩. ⟨hal-04084556⟩
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