A first principles study on structural, dynamical, and mechanical stability of newly predicted delafossite HCoO₂ at high pressure

Abstract

Cobalt oxyhydroxide (HCoO2), which belongs to the heterogenite mineral family, exists in two hexagonal polytypes (2H) and rhombohedral (3R). Here, we investigate the high pressure behaviour of both polytypes of HCoO2 using state‐of‐the‐art first principles calculations‐based density functional theory. We have used both local density approximation (LDA) and generalised gradient approximation (GGA) for exchange correlation functional. For the calculation of electronic band structures, we have also used the on‐site Coulomb interaction U term with LDA calculations and found improvement in results. The obtained ground state properties for both polytypes agree well with experimental and previous theoretical data. The electronic band structure shows that both phases are semiconductor with an indirect band gap in the ran\ge of 2.01–2.06 eV. The pressure‐dependent phonon dispersion curves and elastic constants depict the instability of 2H and 3R phases around 35 and 40 GPa, respectively. The O‐H distance gradually decreases for both phases with pressure and results into the less compressibility in z‐direction. The theoretically calculated pressure‐dependent Raman spectra of 2H‐HCoO2 show the peak broadening nature of E2g mode with pressure whereas in the case of 3R‐HCoO2, the A1g mode disappears beyond 45 GPa pressure. This indicates the existence of phase transition beginning around this pressure, which is driven by the shear modulus. A detailed analysis of the mode compatibility in the case of 2H polytypes is also reported. The phonon mode evolution with pressure is also analysed.

Two‐dimensional CoOOH as a Highly Sensitive and Selective H2S, HCN and HF Gas Sensor: A Computational Investigation

“…The electronic bands are presented along the ΓÀ KÀ MÀ Γ symmetric points. Comparing with the previous study by Upadhyay et al [57,58], we find that the difference in the electronic band structures between the PBE and HSE06 calculations was high since PBE functional are known to underestimate the bandgap of 2D materials [59]. The total and projected density of states are shown in Figure 1c.…”

Nitriding synthesis and structural change of phosphorus nitrides at high pressures

“…Recent advanced density‐functional theory calculations have been successfully used to simulate the compression behaviors of HCoO 2 , thereby revealing that the lower compressibility in the z ‐direction is due to the shortening of the O–H distances with increasing pressure. [ 42 ] γ‐P 3 N 5 consists of corner‐ and edge‐sharing PN 4 and PN 5 polyhedrons, and a large interatomic space exists in the a – c plane. [ 19 ] Thus, the a ‐ and c ‐axes were preferentially compressed via the folding of connected polyhedra, whereas nitrogen and phosphorus atoms were tightly aligned along the b ‐axis, which rigidly constrained the folding of the polyhedra and resulted in the lower compressibility of the b ‐axis.…”

Top‐Level Design Strategy to Construct an Advanced High‐Entropy Co–Cu–Fe–Mo (Oxy)Hydroxide Electrocatalyst for the Oxygen Evolution Reaction

“…The CoCuFeMoOOH nanosheets are further characterized with Raman spectroscopy and X‐ray photoelectron spectroscopy (XPS). In contrast to CoCuFeMoO x , the Raman spectrum of CoCuFeMoOOH (Figure 3a) shows broad and overlapped bands of 515 cm –1 that are attributed to CoOOH, [ 38 ] implying the low degree of crystallinity. [ 39 ] This is in accordance with the broaden diffraction peaks in its XRD pattern (Figure 2e) and the short‐range lattice fringes in the HRTEM image (Figure 2g).…”