Abstract
VOCl and other transition metal oxychlorides are candidate materials for next-generation rechargeable batteries. We have investigated the influence of the underlying magnetic order on the crystallographic and electronic structure by means of density functional theory. Our study shows that antiferromagnetic ordering explains the observed low-temperature monoclinic distortion of the lattice, which leads to a decreased distance between antiferromagnetically coupled V–V nearest neighbors. We also show that the existence of a local magnetic moment removes the previously suggested degeneracy of the occupied levels, in agreement with experiments. To describe the electronic structure, it turns out crucial to take the correct magnetic ordering into account, especially at elevated temperature.
Highlights
The ever increasing need of efficient energy storage solutions is currently driving the search for economical and environmentally friendly options beyond the lithiumion battery
The monoclinic distortion In order to investigate the relation between structure and magnetic order below the Neel temperature, we have used 2 × 2 × 2 supercell with AFM order among the V atoms, as illustrated in figure 2
Electronic structure In figure 4(a) we show the total density of states (DOS) calculated with Ueff = 2 eV for the optimized structure, assuming AFM order
Summary
The ever increasing need of efficient energy storage solutions is currently driving the search for economical and environmentally friendly options beyond the lithiumion battery. The orthorhombic M OCl crystal structure consists of layers of interconnected, distorted M O4Cl2 octahedra separated by a van der Waals gap (see figure 1). This may lead to highly anisotropic interactions due to reduced dimensionality. At 2 K, the monoclinic angle between the a and b axes deviates from orthogonality by 0.2◦ This distortion makes the distance between V3+ ions with anti-parallel magnetic moments shorter by ∼ 0.01 ̊A. We. perform full structural relaxation with different magnetic configurations to show that the monoclinic distortion is a direct consequence of AFM ordering.
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