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Puzzling polymorphism of layered Ba(CoPO4)2
Rénald David1, Houria Kabbour, Alain Pautrat
1Université Lille Nord de France, UMR 8181 CNRS, Unité de Catalyse et de Chimie du Solide (UCCS USTL), F-59655 Villeneuve d'Ascq, France.
Inorganic Chemistry
|July 24, 2013
Summary
This study reveals new crystal structures and magnetic properties of Ba(CoPO4)2, detailing phase transitions and magnetic ordering in layered cobalt phosphate compounds. The findings shed light on frustrated magnetic topology in 2D materials.
Area of Science:
- Materials Science
- Solid State Chemistry
- Magnetism
Background:
- The rhombohedral γ-Ba(CoPO4)2 is known for its quasi-2D XY topology and magnetization steps.
- Layered cobalt phosphates offer potential for exploring complex magnetic phenomena.
Purpose of the Study:
- To investigate the phase diagram and magnetic properties of Ba(CoPO4)2.
- To characterize a newly discovered room-temperature stable monoclinic α form and its high-temperature polymorphs.
- To elucidate the magnetic interactions and frustrated topology in this layered material.
Main Methods:
- High-temperature powder X-ray diffraction (XRD) and thermal analyses (DTA).
- Structural resolution of polymorphs.
- Magnetic susceptibility measurements.
Main Results:
- A new monoclinic α form of Ba(CoPO4)2 was identified, structurally related to Ba(CoPO4)2·H2O.
- Heating the α form leads to reversible transitions (α → α' → α″ → β) with distinct layered architectures.
- The trigonal β phase is isomorphic to CaZn2P2O8 and BaAl2Si2O8.
- The α form exhibits antiferromagnetic ordering at 17 K with canted spins, indicative of a hexagonal frustrated topology due to superexchange and supersuperexchange interactions.
Conclusions:
- The study establishes the phase diagram and crystallographic relationships of Ba(CoPO4)2 polymorphs.
- The magnetic behavior is linked to a 2D frustrated topology arising from anisotropic Co(2+) ions within layered structures.
- This work contributes to understanding magnetic frustration in low-dimensional materials.
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