Understanding the motional dynamics of the ammonium ion in the mechanism of multiferroicity of Cr(V) peroxychromates: a 1H NMR study.
Phys Chem Chem Phys
; 2024 Sep 13.
Article
en En
| MEDLINE
| ID: mdl-39268918
ABSTRACT
Cr(5+)-based peroxychromates, M3Cr(O2)4, with M = NH4 or a mixed NH4-alkali metal are a new class of multiferroics for potential use in molecular memory devices, with the NH4+ being a key element, but the underlying chemical mechanism is not fully understood. The NH4+ ion occupies two different sites, but their specific roles are not known. We thus performed detailed 1H NMR spin-relaxation (T1) measurements on (NH4)3Cr(O2)4 over a wide temperature range (120-300 K) to probe the displacive as well as hindered rotational dynamics of the NH4+ ions with the view of understanding their specific roles in the phase transitions. The NH4+ dynamics is seen to consist of at least three different processes with varying activation energies. The sharp jump in the T1 at around 250 K is assigned to the change in the displacive motion at one of the two sites, while a kink around 140 K is ascribed to motional slowing at the second site. Interestingly, the slowing down starts around 250 K, well above the structural phase transition at 140 K. Taken together, these results provide a clue to the role of the site and symmetry of the NH4+ ion in the mechanism of solid-solid phase transitions.
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Colección:
01-internacional
Base de datos:
MEDLINE
Idioma:
En
Revista:
Phys Chem Chem Phys
Asunto de la revista:
BIOFISICA
/
QUIMICA
Año:
2024
Tipo del documento:
Article
País de afiliación:
India
Pais de publicación:
Reino Unido