Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 1705.10525

Crystal structure of cobalt hydroxide carbonate Co$_2$CO$_3$(OH)$_2$: density functional theory and X-ray diffraction investigation

Jorge González-López·Jeremy K. Cockcroft·Ángeles Fernández-González·Amalia Jimenez·Ricardo Grau-Crespo
View original source ↗Read source document ↗Export metadata ↓

Abstract

We have investigated the structure of Co$_2$CO$_3$(OH)$_2$ using Density Functional Theory (DFT) simulations as well as Powder X-Ray Diffraction (PXRD) measurements on samples synthesized via deposition from aqueous solution. We consider two possible monoclinic phases, with closely related but symmetrically different crystal structures, based on those of the minerals malachite and rosasite, as well as an orthorhombic phase that can be seen as a common parent structure for the two monoclinic phases, and a triclinic phase with the structure of the mineral kolwezite. Our DFT simulations predict that the rosasite-like and the malachite-like phases are two different local minima of the potential energy landscape for Co$_2$CO$_3$(OH)$_2$, and are practically degenerate in energy, while the orthorhombic and triclinic structures are unstable and experience barrierless transformations to the malachite phase upon relaxation. The best fit to the PXRD data is obtained using a rosasite model (monoclinic with space group P1121/n and cell parameters a = 3.1408(4) Å, b = 12.2914(17) Å, c = 9.3311(16) Å, $γ$ = 82.299(16)$^{\circ}$). However, some features of the PXRD pattern are still not well accounted for by this refinement and the residual parameters are relatively poor. We discuss the relationship between the rosasite and malachite phases of Co$_2$CO$_3$(OH)$_2$ and show that they can be seen as polytypes. Based on the similar calculated stability of these two polytypes, we speculate that some level of stacking disorder could account for the poor fit of our PXRD data. The possibility that Co$_2$CO$_3$(OH)$_2$ could crystallize, under different growth conditions, as either rosasite or malachite, or even as a stacking-disordered phase intermediate between the two, requires further investigation.

Explore related subjects

cond-mat.mtrl-sci

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Jorge González-López, Jeremy K. Cockcroft, Ángeles Fernández-González, Amalia Jimenez, Ricardo Grau-Crespo. 2017-05-30. Crystal structure of cobalt hydroxide carbonate Co$_2$CO$_3$(OH)$_2$: density functional theory and X-ray diffraction investigation. https://arxiv.org/abs/1705.10525

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Symmetry-induced magnetic fullerene

Defect-free, charge-neutral, pure-carbon materials are generally viewed as intrinsically non-magnetic. Here we challenge this view by establishing a fundamental principle of symmetry-induced magnetism in pure-carbon fullerene systems through molecular orbital theory. We show that high-order symmetry of fullerene molecules or their crystalline lattices induces degenerate energy levels and hence, quantised magnetic moments at half filling. This mechanism holds for all high-order symmetries. It suggests a plausible intrinsic origin for the previously debated magnetic fullerene. Additionally, recent experimental advances in the synthesis of monolayer fullerene networks provide a feasible platform to implement our prediction on the deep link between symmetry and magnetism in these systems. Our results create new, broad frontiers of quantum magnetism by introducing molecular or crystalline symmetries in any lattice.

cond-mat.mtrl-sci↗
arXiv2026

Tritium for Nanoscale Hydrogen Analysis by Atom Probe Tomography

Accurate nanoscale detection of hydrogen is essential for understanding hydrogen-related phenomena in materials, yet conventional tracing with deuterium is often complicated by residual background hydrogen. This study evaluates tritium as a highly resolvable isotopic marker for nanoscale hydrogen analysis in metals using atom probe tomography. Titanium was selected for its ability to incorporate hydrogen isotopes, providing a suitable platform for tritium detection. Time of flight secondary ion mass spectrometry and electron backscatter diffraction were performed prior to tritium charging to characterize the initial composition and microstructure. Atom probe tomography in laser mode before and after tritium charging, at three post-charging time intervals, enables tracking of tritium incorporation over time. Thermal desorption analysis confirmed the presence of tritium and complemented the secondary ion mass spectrometry measurements, highlighting the role of the surface oxide layer in modulating tritium release. While tritium, deuterium, and protium differ in their diffusion and trapping behavior, the distinct mass signal associated with tritium provides a practical advantage for resolving hydrogen at very low concentrations. This work serves as a fundamental benchmarking study for leveraging tritium and atom probe tomography as a combined tool for understanding hydrogen in materials, relevant for interpreting local processes such as hydrogen embrittlement.

cond-mat.mtrl-sci↗
arXiv2026

Interfacial melting as a thermodynamic indicator of solid-state synthesizability

Computational materials discovery commonly ranks candidate materials by their thermodynamic stability on the formation energy convex hull, yet many predicted-stable phases resist synthesis. We propose that solid-state synthesizability through interfacial-melt-mediated routes requires an additional thermodynamic condition: the interfacial melt at the target composition must itself remain locally stable against spinodal decomposition. We examine this in the classical Fe--B system, where thermodynamically stable FeB$_4$ has been reported under high-pressure synthesis but not in low-pressure synthesis attempts. Using melt--quench molecular dynamics driven by a fine-tuned machine-learning interatomic potential, we find that, at ambient pressure, the B-rich interfacial melt near the FeB$_4$ composition develops a concave free-energy landscape, signaling a demixing instability that is corroborated by the concentration--concentration structure factor and correlated with low-energy icosahedral and pentagonal-pyramidal boron motifs. In contrast to FeB$_4$, metastable Fe$_3$B and Fe$_{23}$B$_6$ remain synthesizable because their corresponding melts are stable. Applied pressure introduces a convex $PV$ contribution that strongly suppresses this instability, reducing the curvature at the FeB$_4$ composition to within the uncertainty of our fit at 1800~K, consistent with the experimental synthesis boundary. Comparison with CrB$_4$ further shows that weaker melt instability correlates with easier experimental synthesis. Interfacial-melt stability, which atomistic simulations can assess via the low-$k$ concentration--concentration structure factor, is thus proposed as a practical thermodynamic screening descriptor of synthesizability for AI-assisted materials discovery.

cond-mat.mtrl-sci↗