Mise en évidence d'un ordre a courte distance dans la phase II des cristaux de NH4Cl, rappelant la phase III des cristaux de NH4Br

Abstract

Reçu le 18 mars 1974) Résumé. 2014 Par diffusion de rayons X et par diffusion Raman, on montre l'importance des phonons aux points 0393 et M de la zone de Brillouin dans la phase II désordonnée de NH4Cl. Les résultats sont interprétés en termes de domaines de fluctuation et d'ordre à courte distance correspondant aux arrangements parallèles et antiparallèles des 2 phases ordonnées déjà connues pour les halogénures d'ammonium. Abstract. 2014 Experimental studies of X-ray scattering and Raman scattering have shown the importance of the contributions of phonons at the 0393 and M points of the Brillouin zone in the disordered phase II of NH4Cl. The results are interpreted in terms of fluctuation domains and a short range order corresponding to the known parallel and antiparallel arrangements of the 2 ordered phases of the ammonium halides.

Order-disorder transition ofND4ClandNH4Seeck1, Hupfeld2, Krull3 et al. 1998Phys. Rev. B190110View full textAdd to dashboardCite

“…They may occur in the disordered as well as in the F-ordered phase. First indications of AF fluctuations in NH 4 Cl were published by Couzi et al 15 Our synchrotron x-ray measurements clearly prove the presence of AF fluctuations in ND 4 Cl and NH 4 Cl which were recorded over a wide temperature range for the two materials.…”

Calculation of the specific heat close to the multicritical and second order phase regions in ND4Cl

“…On the other hand, very recently, it has been claimed that due to the competing interactions in NX 4 Cl (X = H, D) crystals, fluctuations of an AF-ordered phase can occur in both the disordered (b) and F-ordered (d) phases [23]. On the basis of the first indications of AF fluctuations in NH 4 Cl [24], this was recorded by X-ray measurements in ND 4 Cl and NH 4 Cl [23]. It was noted that AF fluctuations are considerably weaker in ND 4 Cl [23].…”

Electro-optic measurement of the order parameter of NH4Cl

“…A tendency towards an antiparallel order in NH4Cl is shown in the diffuse X-ray scattering produced at room temperature by thermal fluctuations [7].…”