Hydration-Controlled Layer Stacking in (NH$_3$)$_2$Cu$_5$(SeO$_3$)$_2$(OH)$_6$(H$_2$O)$_{2+x}$ ($x$ = 0, 1, and 3)
Authors:
Priya R. Baral,
Christian Jandl,
Pauline Pradal,
Johann Roos,
Wenhua Bi,
Arnaud Magrez
Abstract:
Hydration and dehydration are powerful yet underexplored variables for controlling the architecture of layered inorganic materials, because intercalated water can modify interlayer separation, hydrogen-bonding networks, and layer stacking. Here, we report the reflux synthesis of a new family of hydrated layered copper selenites, (NH$_3$)$_2$Cu$_5$(SeO$_3$)$_2$(OH)$_6$(H$_2$O)$_{2+x}$ ($x$ = 0, 1,…
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Hydration and dehydration are powerful yet underexplored variables for controlling the architecture of layered inorganic materials, because intercalated water can modify interlayer separation, hydrogen-bonding networks, and layer stacking. Here, we report the reflux synthesis of a new family of hydrated layered copper selenites, (NH$_3$)$_2$Cu$_5$(SeO$_3$)$_2$(OH)$_6$(H$_2$O)$_{2+x}$ ($x$ = 0, 1, and 3). From the crystal structures determined using electron diffraction and single crystal X-ray diffraction, we deduce that all three compounds share an identical layer built from Cu(OH)$_4$ squares and Cu-centered square pyramids forming distorted kagomé-like Cu$^{2+}$ network. While the intralayer atomic arrangement is preserved across the series, the degree of hydration governs both the interlayer separation and the stacking sequence. These compounds therefore provide a rare platform relevant to the design of hydration-responsive materials for sensing, ion transport, separations, actuation, and energy-related applications. The preservation of distorted kagomé-like Cu$^{2+}$ layers across hydration states further suggests potential interest for examining how interlayer water and stacking sequence affect low-dimensional magnetic coupling. Under reflux conditions, these phases are also shown to act as reactive intermediates in the formation of Cu$_2$OSeO$_3$, establishing them as tunable precursors for copper oxoselenite synthesis.
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Submitted 30 July, 2026;
originally announced July 2026.
Cu2OSeO3 Turns Trigonal with Structural Transformation and Implications for Skyrmions
Authors:
Alla Arakcheeva,
Priya Ranjan Baral,
Wen Hua Bi,
Christian Jandl,
Oleg Janson,
Arnaud Magrez
Abstract:
The formation and characteristics of magnetic skyrmions are strongly governed by the symmetry of the underlying crystal structure. In this study, we report the discovery of a new trigonal polymorph of Cu2OSeO3, observed exclusively in nanoparticles. Electron diffraction and density functional theory calculations confirm its R3m space group, sharing C3v symmetry with Néel-type skyrmion hosts. This…
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The formation and characteristics of magnetic skyrmions are strongly governed by the symmetry of the underlying crystal structure. In this study, we report the discovery of a new trigonal polymorph of Cu2OSeO3, observed exclusively in nanoparticles. Electron diffraction and density functional theory calculations confirm its R3m space group, sharing C3v symmetry with Néel-type skyrmion hosts. This polymorph is likely stabilized by surface effects, suggesting that size-induced structural changes may drive a transformation from Bloch-type to Neel-type skyrmions in Cu2OSeO3. This hypothesis is consistent with prior unexplained observations of Neel-type skyrmions at the surfaces of bulk crystals, which may result from surface-specific structural distortions. Overall, these findings provide insights into the interplay between size, structure, and magnetism, opening pathways for controlling skyrmionic properties in nanoscale systems.
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Submitted 11 August, 2025;
originally announced August 2025.